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Merge remote-tracking branch 'mkp-scsi/4.9/scsi-fixes' into fixes
[karo-tx-linux.git] / mm / swapfile.c
1 /*
2  *  linux/mm/swapfile.c
3  *
4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
5  *  Swap reorganised 29.12.95, Stephen Tweedie
6  */
7
8 #include <linux/mm.h>
9 #include <linux/hugetlb.h>
10 #include <linux/mman.h>
11 #include <linux/slab.h>
12 #include <linux/kernel_stat.h>
13 #include <linux/swap.h>
14 #include <linux/vmalloc.h>
15 #include <linux/pagemap.h>
16 #include <linux/namei.h>
17 #include <linux/shmem_fs.h>
18 #include <linux/blkdev.h>
19 #include <linux/random.h>
20 #include <linux/writeback.h>
21 #include <linux/proc_fs.h>
22 #include <linux/seq_file.h>
23 #include <linux/init.h>
24 #include <linux/ksm.h>
25 #include <linux/rmap.h>
26 #include <linux/security.h>
27 #include <linux/backing-dev.h>
28 #include <linux/mutex.h>
29 #include <linux/capability.h>
30 #include <linux/syscalls.h>
31 #include <linux/memcontrol.h>
32 #include <linux/poll.h>
33 #include <linux/oom.h>
34 #include <linux/frontswap.h>
35 #include <linux/swapfile.h>
36 #include <linux/export.h>
37
38 #include <asm/pgtable.h>
39 #include <asm/tlbflush.h>
40 #include <linux/swapops.h>
41 #include <linux/swap_cgroup.h>
42
43 static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
44                                  unsigned char);
45 static void free_swap_count_continuations(struct swap_info_struct *);
46 static sector_t map_swap_entry(swp_entry_t, struct block_device**);
47
48 DEFINE_SPINLOCK(swap_lock);
49 static unsigned int nr_swapfiles;
50 atomic_long_t nr_swap_pages;
51 /*
52  * Some modules use swappable objects and may try to swap them out under
53  * memory pressure (via the shrinker). Before doing so, they may wish to
54  * check to see if any swap space is available.
55  */
56 EXPORT_SYMBOL_GPL(nr_swap_pages);
57 /* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
58 long total_swap_pages;
59 static int least_priority;
60
61 static const char Bad_file[] = "Bad swap file entry ";
62 static const char Unused_file[] = "Unused swap file entry ";
63 static const char Bad_offset[] = "Bad swap offset entry ";
64 static const char Unused_offset[] = "Unused swap offset entry ";
65
66 /*
67  * all active swap_info_structs
68  * protected with swap_lock, and ordered by priority.
69  */
70 PLIST_HEAD(swap_active_head);
71
72 /*
73  * all available (active, not full) swap_info_structs
74  * protected with swap_avail_lock, ordered by priority.
75  * This is used by get_swap_page() instead of swap_active_head
76  * because swap_active_head includes all swap_info_structs,
77  * but get_swap_page() doesn't need to look at full ones.
78  * This uses its own lock instead of swap_lock because when a
79  * swap_info_struct changes between not-full/full, it needs to
80  * add/remove itself to/from this list, but the swap_info_struct->lock
81  * is held and the locking order requires swap_lock to be taken
82  * before any swap_info_struct->lock.
83  */
84 static PLIST_HEAD(swap_avail_head);
85 static DEFINE_SPINLOCK(swap_avail_lock);
86
87 struct swap_info_struct *swap_info[MAX_SWAPFILES];
88
89 static DEFINE_MUTEX(swapon_mutex);
90
91 static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
92 /* Activity counter to indicate that a swapon or swapoff has occurred */
93 static atomic_t proc_poll_event = ATOMIC_INIT(0);
94
95 static inline unsigned char swap_count(unsigned char ent)
96 {
97         return ent & ~SWAP_HAS_CACHE;   /* may include SWAP_HAS_CONT flag */
98 }
99
100 /* returns 1 if swap entry is freed */
101 static int
102 __try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
103 {
104         swp_entry_t entry = swp_entry(si->type, offset);
105         struct page *page;
106         int ret = 0;
107
108         page = find_get_page(swap_address_space(entry), swp_offset(entry));
109         if (!page)
110                 return 0;
111         /*
112          * This function is called from scan_swap_map() and it's called
113          * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
114          * We have to use trylock for avoiding deadlock. This is a special
115          * case and you should use try_to_free_swap() with explicit lock_page()
116          * in usual operations.
117          */
118         if (trylock_page(page)) {
119                 ret = try_to_free_swap(page);
120                 unlock_page(page);
121         }
122         put_page(page);
123         return ret;
124 }
125
126 /*
127  * swapon tell device that all the old swap contents can be discarded,
128  * to allow the swap device to optimize its wear-levelling.
129  */
130 static int discard_swap(struct swap_info_struct *si)
131 {
132         struct swap_extent *se;
133         sector_t start_block;
134         sector_t nr_blocks;
135         int err = 0;
136
137         /* Do not discard the swap header page! */
138         se = &si->first_swap_extent;
139         start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
140         nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
141         if (nr_blocks) {
142                 err = blkdev_issue_discard(si->bdev, start_block,
143                                 nr_blocks, GFP_KERNEL, 0);
144                 if (err)
145                         return err;
146                 cond_resched();
147         }
148
149         list_for_each_entry(se, &si->first_swap_extent.list, list) {
150                 start_block = se->start_block << (PAGE_SHIFT - 9);
151                 nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
152
153                 err = blkdev_issue_discard(si->bdev, start_block,
154                                 nr_blocks, GFP_KERNEL, 0);
155                 if (err)
156                         break;
157
158                 cond_resched();
159         }
160         return err;             /* That will often be -EOPNOTSUPP */
161 }
162
163 /*
164  * swap allocation tell device that a cluster of swap can now be discarded,
165  * to allow the swap device to optimize its wear-levelling.
166  */
167 static void discard_swap_cluster(struct swap_info_struct *si,
168                                  pgoff_t start_page, pgoff_t nr_pages)
169 {
170         struct swap_extent *se = si->curr_swap_extent;
171         int found_extent = 0;
172
173         while (nr_pages) {
174                 if (se->start_page <= start_page &&
175                     start_page < se->start_page + se->nr_pages) {
176                         pgoff_t offset = start_page - se->start_page;
177                         sector_t start_block = se->start_block + offset;
178                         sector_t nr_blocks = se->nr_pages - offset;
179
180                         if (nr_blocks > nr_pages)
181                                 nr_blocks = nr_pages;
182                         start_page += nr_blocks;
183                         nr_pages -= nr_blocks;
184
185                         if (!found_extent++)
186                                 si->curr_swap_extent = se;
187
188                         start_block <<= PAGE_SHIFT - 9;
189                         nr_blocks <<= PAGE_SHIFT - 9;
190                         if (blkdev_issue_discard(si->bdev, start_block,
191                                     nr_blocks, GFP_NOIO, 0))
192                                 break;
193                 }
194
195                 se = list_next_entry(se, list);
196         }
197 }
198
199 #define SWAPFILE_CLUSTER        256
200 #define LATENCY_LIMIT           256
201
202 static inline void cluster_set_flag(struct swap_cluster_info *info,
203         unsigned int flag)
204 {
205         info->flags = flag;
206 }
207
208 static inline unsigned int cluster_count(struct swap_cluster_info *info)
209 {
210         return info->data;
211 }
212
213 static inline void cluster_set_count(struct swap_cluster_info *info,
214                                      unsigned int c)
215 {
216         info->data = c;
217 }
218
219 static inline void cluster_set_count_flag(struct swap_cluster_info *info,
220                                          unsigned int c, unsigned int f)
221 {
222         info->flags = f;
223         info->data = c;
224 }
225
226 static inline unsigned int cluster_next(struct swap_cluster_info *info)
227 {
228         return info->data;
229 }
230
231 static inline void cluster_set_next(struct swap_cluster_info *info,
232                                     unsigned int n)
233 {
234         info->data = n;
235 }
236
237 static inline void cluster_set_next_flag(struct swap_cluster_info *info,
238                                          unsigned int n, unsigned int f)
239 {
240         info->flags = f;
241         info->data = n;
242 }
243
244 static inline bool cluster_is_free(struct swap_cluster_info *info)
245 {
246         return info->flags & CLUSTER_FLAG_FREE;
247 }
248
249 static inline bool cluster_is_null(struct swap_cluster_info *info)
250 {
251         return info->flags & CLUSTER_FLAG_NEXT_NULL;
252 }
253
254 static inline void cluster_set_null(struct swap_cluster_info *info)
255 {
256         info->flags = CLUSTER_FLAG_NEXT_NULL;
257         info->data = 0;
258 }
259
260 static inline bool cluster_list_empty(struct swap_cluster_list *list)
261 {
262         return cluster_is_null(&list->head);
263 }
264
265 static inline unsigned int cluster_list_first(struct swap_cluster_list *list)
266 {
267         return cluster_next(&list->head);
268 }
269
270 static void cluster_list_init(struct swap_cluster_list *list)
271 {
272         cluster_set_null(&list->head);
273         cluster_set_null(&list->tail);
274 }
275
276 static void cluster_list_add_tail(struct swap_cluster_list *list,
277                                   struct swap_cluster_info *ci,
278                                   unsigned int idx)
279 {
280         if (cluster_list_empty(list)) {
281                 cluster_set_next_flag(&list->head, idx, 0);
282                 cluster_set_next_flag(&list->tail, idx, 0);
283         } else {
284                 unsigned int tail = cluster_next(&list->tail);
285
286                 cluster_set_next(&ci[tail], idx);
287                 cluster_set_next_flag(&list->tail, idx, 0);
288         }
289 }
290
291 static unsigned int cluster_list_del_first(struct swap_cluster_list *list,
292                                            struct swap_cluster_info *ci)
293 {
294         unsigned int idx;
295
296         idx = cluster_next(&list->head);
297         if (cluster_next(&list->tail) == idx) {
298                 cluster_set_null(&list->head);
299                 cluster_set_null(&list->tail);
300         } else
301                 cluster_set_next_flag(&list->head,
302                                       cluster_next(&ci[idx]), 0);
303
304         return idx;
305 }
306
307 /* Add a cluster to discard list and schedule it to do discard */
308 static void swap_cluster_schedule_discard(struct swap_info_struct *si,
309                 unsigned int idx)
310 {
311         /*
312          * If scan_swap_map() can't find a free cluster, it will check
313          * si->swap_map directly. To make sure the discarding cluster isn't
314          * taken by scan_swap_map(), mark the swap entries bad (occupied). It
315          * will be cleared after discard
316          */
317         memset(si->swap_map + idx * SWAPFILE_CLUSTER,
318                         SWAP_MAP_BAD, SWAPFILE_CLUSTER);
319
320         cluster_list_add_tail(&si->discard_clusters, si->cluster_info, idx);
321
322         schedule_work(&si->discard_work);
323 }
324
325 /*
326  * Doing discard actually. After a cluster discard is finished, the cluster
327  * will be added to free cluster list. caller should hold si->lock.
328 */
329 static void swap_do_scheduled_discard(struct swap_info_struct *si)
330 {
331         struct swap_cluster_info *info;
332         unsigned int idx;
333
334         info = si->cluster_info;
335
336         while (!cluster_list_empty(&si->discard_clusters)) {
337                 idx = cluster_list_del_first(&si->discard_clusters, info);
338                 spin_unlock(&si->lock);
339
340                 discard_swap_cluster(si, idx * SWAPFILE_CLUSTER,
341                                 SWAPFILE_CLUSTER);
342
343                 spin_lock(&si->lock);
344                 cluster_set_flag(&info[idx], CLUSTER_FLAG_FREE);
345                 cluster_list_add_tail(&si->free_clusters, info, idx);
346                 memset(si->swap_map + idx * SWAPFILE_CLUSTER,
347                                 0, SWAPFILE_CLUSTER);
348         }
349 }
350
351 static void swap_discard_work(struct work_struct *work)
352 {
353         struct swap_info_struct *si;
354
355         si = container_of(work, struct swap_info_struct, discard_work);
356
357         spin_lock(&si->lock);
358         swap_do_scheduled_discard(si);
359         spin_unlock(&si->lock);
360 }
361
362 /*
363  * The cluster corresponding to page_nr will be used. The cluster will be
364  * removed from free cluster list and its usage counter will be increased.
365  */
366 static void inc_cluster_info_page(struct swap_info_struct *p,
367         struct swap_cluster_info *cluster_info, unsigned long page_nr)
368 {
369         unsigned long idx = page_nr / SWAPFILE_CLUSTER;
370
371         if (!cluster_info)
372                 return;
373         if (cluster_is_free(&cluster_info[idx])) {
374                 VM_BUG_ON(cluster_list_first(&p->free_clusters) != idx);
375                 cluster_list_del_first(&p->free_clusters, cluster_info);
376                 cluster_set_count_flag(&cluster_info[idx], 0, 0);
377         }
378
379         VM_BUG_ON(cluster_count(&cluster_info[idx]) >= SWAPFILE_CLUSTER);
380         cluster_set_count(&cluster_info[idx],
381                 cluster_count(&cluster_info[idx]) + 1);
382 }
383
384 /*
385  * The cluster corresponding to page_nr decreases one usage. If the usage
386  * counter becomes 0, which means no page in the cluster is in using, we can
387  * optionally discard the cluster and add it to free cluster list.
388  */
389 static void dec_cluster_info_page(struct swap_info_struct *p,
390         struct swap_cluster_info *cluster_info, unsigned long page_nr)
391 {
392         unsigned long idx = page_nr / SWAPFILE_CLUSTER;
393
394         if (!cluster_info)
395                 return;
396
397         VM_BUG_ON(cluster_count(&cluster_info[idx]) == 0);
398         cluster_set_count(&cluster_info[idx],
399                 cluster_count(&cluster_info[idx]) - 1);
400
401         if (cluster_count(&cluster_info[idx]) == 0) {
402                 /*
403                  * If the swap is discardable, prepare discard the cluster
404                  * instead of free it immediately. The cluster will be freed
405                  * after discard.
406                  */
407                 if ((p->flags & (SWP_WRITEOK | SWP_PAGE_DISCARD)) ==
408                                  (SWP_WRITEOK | SWP_PAGE_DISCARD)) {
409                         swap_cluster_schedule_discard(p, idx);
410                         return;
411                 }
412
413                 cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
414                 cluster_list_add_tail(&p->free_clusters, cluster_info, idx);
415         }
416 }
417
418 /*
419  * It's possible scan_swap_map() uses a free cluster in the middle of free
420  * cluster list. Avoiding such abuse to avoid list corruption.
421  */
422 static bool
423 scan_swap_map_ssd_cluster_conflict(struct swap_info_struct *si,
424         unsigned long offset)
425 {
426         struct percpu_cluster *percpu_cluster;
427         bool conflict;
428
429         offset /= SWAPFILE_CLUSTER;
430         conflict = !cluster_list_empty(&si->free_clusters) &&
431                 offset != cluster_list_first(&si->free_clusters) &&
432                 cluster_is_free(&si->cluster_info[offset]);
433
434         if (!conflict)
435                 return false;
436
437         percpu_cluster = this_cpu_ptr(si->percpu_cluster);
438         cluster_set_null(&percpu_cluster->index);
439         return true;
440 }
441
442 /*
443  * Try to get a swap entry from current cpu's swap entry pool (a cluster). This
444  * might involve allocating a new cluster for current CPU too.
445  */
446 static void scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
447         unsigned long *offset, unsigned long *scan_base)
448 {
449         struct percpu_cluster *cluster;
450         bool found_free;
451         unsigned long tmp;
452
453 new_cluster:
454         cluster = this_cpu_ptr(si->percpu_cluster);
455         if (cluster_is_null(&cluster->index)) {
456                 if (!cluster_list_empty(&si->free_clusters)) {
457                         cluster->index = si->free_clusters.head;
458                         cluster->next = cluster_next(&cluster->index) *
459                                         SWAPFILE_CLUSTER;
460                 } else if (!cluster_list_empty(&si->discard_clusters)) {
461                         /*
462                          * we don't have free cluster but have some clusters in
463                          * discarding, do discard now and reclaim them
464                          */
465                         swap_do_scheduled_discard(si);
466                         *scan_base = *offset = si->cluster_next;
467                         goto new_cluster;
468                 } else
469                         return;
470         }
471
472         found_free = false;
473
474         /*
475          * Other CPUs can use our cluster if they can't find a free cluster,
476          * check if there is still free entry in the cluster
477          */
478         tmp = cluster->next;
479         while (tmp < si->max && tmp < (cluster_next(&cluster->index) + 1) *
480                SWAPFILE_CLUSTER) {
481                 if (!si->swap_map[tmp]) {
482                         found_free = true;
483                         break;
484                 }
485                 tmp++;
486         }
487         if (!found_free) {
488                 cluster_set_null(&cluster->index);
489                 goto new_cluster;
490         }
491         cluster->next = tmp + 1;
492         *offset = tmp;
493         *scan_base = tmp;
494 }
495
496 static unsigned long scan_swap_map(struct swap_info_struct *si,
497                                    unsigned char usage)
498 {
499         unsigned long offset;
500         unsigned long scan_base;
501         unsigned long last_in_cluster = 0;
502         int latency_ration = LATENCY_LIMIT;
503
504         /*
505          * We try to cluster swap pages by allocating them sequentially
506          * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
507          * way, however, we resort to first-free allocation, starting
508          * a new cluster.  This prevents us from scattering swap pages
509          * all over the entire swap partition, so that we reduce
510          * overall disk seek times between swap pages.  -- sct
511          * But we do now try to find an empty cluster.  -Andrea
512          * And we let swap pages go all over an SSD partition.  Hugh
513          */
514
515         si->flags += SWP_SCANNING;
516         scan_base = offset = si->cluster_next;
517
518         /* SSD algorithm */
519         if (si->cluster_info) {
520                 scan_swap_map_try_ssd_cluster(si, &offset, &scan_base);
521                 goto checks;
522         }
523
524         if (unlikely(!si->cluster_nr--)) {
525                 if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
526                         si->cluster_nr = SWAPFILE_CLUSTER - 1;
527                         goto checks;
528                 }
529
530                 spin_unlock(&si->lock);
531
532                 /*
533                  * If seek is expensive, start searching for new cluster from
534                  * start of partition, to minimize the span of allocated swap.
535                  * If seek is cheap, that is the SWP_SOLIDSTATE si->cluster_info
536                  * case, just handled by scan_swap_map_try_ssd_cluster() above.
537                  */
538                 scan_base = offset = si->lowest_bit;
539                 last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
540
541                 /* Locate the first empty (unaligned) cluster */
542                 for (; last_in_cluster <= si->highest_bit; offset++) {
543                         if (si->swap_map[offset])
544                                 last_in_cluster = offset + SWAPFILE_CLUSTER;
545                         else if (offset == last_in_cluster) {
546                                 spin_lock(&si->lock);
547                                 offset -= SWAPFILE_CLUSTER - 1;
548                                 si->cluster_next = offset;
549                                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
550                                 goto checks;
551                         }
552                         if (unlikely(--latency_ration < 0)) {
553                                 cond_resched();
554                                 latency_ration = LATENCY_LIMIT;
555                         }
556                 }
557
558                 offset = scan_base;
559                 spin_lock(&si->lock);
560                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
561         }
562
563 checks:
564         if (si->cluster_info) {
565                 while (scan_swap_map_ssd_cluster_conflict(si, offset))
566                         scan_swap_map_try_ssd_cluster(si, &offset, &scan_base);
567         }
568         if (!(si->flags & SWP_WRITEOK))
569                 goto no_page;
570         if (!si->highest_bit)
571                 goto no_page;
572         if (offset > si->highest_bit)
573                 scan_base = offset = si->lowest_bit;
574
575         /* reuse swap entry of cache-only swap if not busy. */
576         if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
577                 int swap_was_freed;
578                 spin_unlock(&si->lock);
579                 swap_was_freed = __try_to_reclaim_swap(si, offset);
580                 spin_lock(&si->lock);
581                 /* entry was freed successfully, try to use this again */
582                 if (swap_was_freed)
583                         goto checks;
584                 goto scan; /* check next one */
585         }
586
587         if (si->swap_map[offset])
588                 goto scan;
589
590         if (offset == si->lowest_bit)
591                 si->lowest_bit++;
592         if (offset == si->highest_bit)
593                 si->highest_bit--;
594         si->inuse_pages++;
595         if (si->inuse_pages == si->pages) {
596                 si->lowest_bit = si->max;
597                 si->highest_bit = 0;
598                 spin_lock(&swap_avail_lock);
599                 plist_del(&si->avail_list, &swap_avail_head);
600                 spin_unlock(&swap_avail_lock);
601         }
602         si->swap_map[offset] = usage;
603         inc_cluster_info_page(si, si->cluster_info, offset);
604         si->cluster_next = offset + 1;
605         si->flags -= SWP_SCANNING;
606
607         return offset;
608
609 scan:
610         spin_unlock(&si->lock);
611         while (++offset <= si->highest_bit) {
612                 if (!si->swap_map[offset]) {
613                         spin_lock(&si->lock);
614                         goto checks;
615                 }
616                 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
617                         spin_lock(&si->lock);
618                         goto checks;
619                 }
620                 if (unlikely(--latency_ration < 0)) {
621                         cond_resched();
622                         latency_ration = LATENCY_LIMIT;
623                 }
624         }
625         offset = si->lowest_bit;
626         while (offset < scan_base) {
627                 if (!si->swap_map[offset]) {
628                         spin_lock(&si->lock);
629                         goto checks;
630                 }
631                 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
632                         spin_lock(&si->lock);
633                         goto checks;
634                 }
635                 if (unlikely(--latency_ration < 0)) {
636                         cond_resched();
637                         latency_ration = LATENCY_LIMIT;
638                 }
639                 offset++;
640         }
641         spin_lock(&si->lock);
642
643 no_page:
644         si->flags -= SWP_SCANNING;
645         return 0;
646 }
647
648 swp_entry_t get_swap_page(void)
649 {
650         struct swap_info_struct *si, *next;
651         pgoff_t offset;
652
653         if (atomic_long_read(&nr_swap_pages) <= 0)
654                 goto noswap;
655         atomic_long_dec(&nr_swap_pages);
656
657         spin_lock(&swap_avail_lock);
658
659 start_over:
660         plist_for_each_entry_safe(si, next, &swap_avail_head, avail_list) {
661                 /* requeue si to after same-priority siblings */
662                 plist_requeue(&si->avail_list, &swap_avail_head);
663                 spin_unlock(&swap_avail_lock);
664                 spin_lock(&si->lock);
665                 if (!si->highest_bit || !(si->flags & SWP_WRITEOK)) {
666                         spin_lock(&swap_avail_lock);
667                         if (plist_node_empty(&si->avail_list)) {
668                                 spin_unlock(&si->lock);
669                                 goto nextsi;
670                         }
671                         WARN(!si->highest_bit,
672                              "swap_info %d in list but !highest_bit\n",
673                              si->type);
674                         WARN(!(si->flags & SWP_WRITEOK),
675                              "swap_info %d in list but !SWP_WRITEOK\n",
676                              si->type);
677                         plist_del(&si->avail_list, &swap_avail_head);
678                         spin_unlock(&si->lock);
679                         goto nextsi;
680                 }
681
682                 /* This is called for allocating swap entry for cache */
683                 offset = scan_swap_map(si, SWAP_HAS_CACHE);
684                 spin_unlock(&si->lock);
685                 if (offset)
686                         return swp_entry(si->type, offset);
687                 pr_debug("scan_swap_map of si %d failed to find offset\n",
688                        si->type);
689                 spin_lock(&swap_avail_lock);
690 nextsi:
691                 /*
692                  * if we got here, it's likely that si was almost full before,
693                  * and since scan_swap_map() can drop the si->lock, multiple
694                  * callers probably all tried to get a page from the same si
695                  * and it filled up before we could get one; or, the si filled
696                  * up between us dropping swap_avail_lock and taking si->lock.
697                  * Since we dropped the swap_avail_lock, the swap_avail_head
698                  * list may have been modified; so if next is still in the
699                  * swap_avail_head list then try it, otherwise start over.
700                  */
701                 if (plist_node_empty(&next->avail_list))
702                         goto start_over;
703         }
704
705         spin_unlock(&swap_avail_lock);
706
707         atomic_long_inc(&nr_swap_pages);
708 noswap:
709         return (swp_entry_t) {0};
710 }
711
712 /* The only caller of this function is now suspend routine */
713 swp_entry_t get_swap_page_of_type(int type)
714 {
715         struct swap_info_struct *si;
716         pgoff_t offset;
717
718         si = swap_info[type];
719         spin_lock(&si->lock);
720         if (si && (si->flags & SWP_WRITEOK)) {
721                 atomic_long_dec(&nr_swap_pages);
722                 /* This is called for allocating swap entry, not cache */
723                 offset = scan_swap_map(si, 1);
724                 if (offset) {
725                         spin_unlock(&si->lock);
726                         return swp_entry(type, offset);
727                 }
728                 atomic_long_inc(&nr_swap_pages);
729         }
730         spin_unlock(&si->lock);
731         return (swp_entry_t) {0};
732 }
733
734 static struct swap_info_struct *swap_info_get(swp_entry_t entry)
735 {
736         struct swap_info_struct *p;
737         unsigned long offset, type;
738
739         if (!entry.val)
740                 goto out;
741         type = swp_type(entry);
742         if (type >= nr_swapfiles)
743                 goto bad_nofile;
744         p = swap_info[type];
745         if (!(p->flags & SWP_USED))
746                 goto bad_device;
747         offset = swp_offset(entry);
748         if (offset >= p->max)
749                 goto bad_offset;
750         if (!p->swap_map[offset])
751                 goto bad_free;
752         spin_lock(&p->lock);
753         return p;
754
755 bad_free:
756         pr_err("swap_free: %s%08lx\n", Unused_offset, entry.val);
757         goto out;
758 bad_offset:
759         pr_err("swap_free: %s%08lx\n", Bad_offset, entry.val);
760         goto out;
761 bad_device:
762         pr_err("swap_free: %s%08lx\n", Unused_file, entry.val);
763         goto out;
764 bad_nofile:
765         pr_err("swap_free: %s%08lx\n", Bad_file, entry.val);
766 out:
767         return NULL;
768 }
769
770 static unsigned char swap_entry_free(struct swap_info_struct *p,
771                                      swp_entry_t entry, unsigned char usage)
772 {
773         unsigned long offset = swp_offset(entry);
774         unsigned char count;
775         unsigned char has_cache;
776
777         count = p->swap_map[offset];
778         has_cache = count & SWAP_HAS_CACHE;
779         count &= ~SWAP_HAS_CACHE;
780
781         if (usage == SWAP_HAS_CACHE) {
782                 VM_BUG_ON(!has_cache);
783                 has_cache = 0;
784         } else if (count == SWAP_MAP_SHMEM) {
785                 /*
786                  * Or we could insist on shmem.c using a special
787                  * swap_shmem_free() and free_shmem_swap_and_cache()...
788                  */
789                 count = 0;
790         } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
791                 if (count == COUNT_CONTINUED) {
792                         if (swap_count_continued(p, offset, count))
793                                 count = SWAP_MAP_MAX | COUNT_CONTINUED;
794                         else
795                                 count = SWAP_MAP_MAX;
796                 } else
797                         count--;
798         }
799
800         usage = count | has_cache;
801         p->swap_map[offset] = usage;
802
803         /* free if no reference */
804         if (!usage) {
805                 mem_cgroup_uncharge_swap(entry);
806                 dec_cluster_info_page(p, p->cluster_info, offset);
807                 if (offset < p->lowest_bit)
808                         p->lowest_bit = offset;
809                 if (offset > p->highest_bit) {
810                         bool was_full = !p->highest_bit;
811                         p->highest_bit = offset;
812                         if (was_full && (p->flags & SWP_WRITEOK)) {
813                                 spin_lock(&swap_avail_lock);
814                                 WARN_ON(!plist_node_empty(&p->avail_list));
815                                 if (plist_node_empty(&p->avail_list))
816                                         plist_add(&p->avail_list,
817                                                   &swap_avail_head);
818                                 spin_unlock(&swap_avail_lock);
819                         }
820                 }
821                 atomic_long_inc(&nr_swap_pages);
822                 p->inuse_pages--;
823                 frontswap_invalidate_page(p->type, offset);
824                 if (p->flags & SWP_BLKDEV) {
825                         struct gendisk *disk = p->bdev->bd_disk;
826                         if (disk->fops->swap_slot_free_notify)
827                                 disk->fops->swap_slot_free_notify(p->bdev,
828                                                                   offset);
829                 }
830         }
831
832         return usage;
833 }
834
835 /*
836  * Caller has made sure that the swap device corresponding to entry
837  * is still around or has not been recycled.
838  */
839 void swap_free(swp_entry_t entry)
840 {
841         struct swap_info_struct *p;
842
843         p = swap_info_get(entry);
844         if (p) {
845                 swap_entry_free(p, entry, 1);
846                 spin_unlock(&p->lock);
847         }
848 }
849
850 /*
851  * Called after dropping swapcache to decrease refcnt to swap entries.
852  */
853 void swapcache_free(swp_entry_t entry)
854 {
855         struct swap_info_struct *p;
856
857         p = swap_info_get(entry);
858         if (p) {
859                 swap_entry_free(p, entry, SWAP_HAS_CACHE);
860                 spin_unlock(&p->lock);
861         }
862 }
863
864 /*
865  * How many references to page are currently swapped out?
866  * This does not give an exact answer when swap count is continued,
867  * but does include the high COUNT_CONTINUED flag to allow for that.
868  */
869 int page_swapcount(struct page *page)
870 {
871         int count = 0;
872         struct swap_info_struct *p;
873         swp_entry_t entry;
874
875         entry.val = page_private(page);
876         p = swap_info_get(entry);
877         if (p) {
878                 count = swap_count(p->swap_map[swp_offset(entry)]);
879                 spin_unlock(&p->lock);
880         }
881         return count;
882 }
883
884 /*
885  * How many references to @entry are currently swapped out?
886  * This considers COUNT_CONTINUED so it returns exact answer.
887  */
888 int swp_swapcount(swp_entry_t entry)
889 {
890         int count, tmp_count, n;
891         struct swap_info_struct *p;
892         struct page *page;
893         pgoff_t offset;
894         unsigned char *map;
895
896         p = swap_info_get(entry);
897         if (!p)
898                 return 0;
899
900         count = swap_count(p->swap_map[swp_offset(entry)]);
901         if (!(count & COUNT_CONTINUED))
902                 goto out;
903
904         count &= ~COUNT_CONTINUED;
905         n = SWAP_MAP_MAX + 1;
906
907         offset = swp_offset(entry);
908         page = vmalloc_to_page(p->swap_map + offset);
909         offset &= ~PAGE_MASK;
910         VM_BUG_ON(page_private(page) != SWP_CONTINUED);
911
912         do {
913                 page = list_next_entry(page, lru);
914                 map = kmap_atomic(page);
915                 tmp_count = map[offset];
916                 kunmap_atomic(map);
917
918                 count += (tmp_count & ~COUNT_CONTINUED) * n;
919                 n *= (SWAP_CONT_MAX + 1);
920         } while (tmp_count & COUNT_CONTINUED);
921 out:
922         spin_unlock(&p->lock);
923         return count;
924 }
925
926 /*
927  * We can write to an anon page without COW if there are no other references
928  * to it.  And as a side-effect, free up its swap: because the old content
929  * on disk will never be read, and seeking back there to write new content
930  * later would only waste time away from clustering.
931  *
932  * NOTE: total_mapcount should not be relied upon by the caller if
933  * reuse_swap_page() returns false, but it may be always overwritten
934  * (see the other implementation for CONFIG_SWAP=n).
935  */
936 bool reuse_swap_page(struct page *page, int *total_mapcount)
937 {
938         int count;
939
940         VM_BUG_ON_PAGE(!PageLocked(page), page);
941         if (unlikely(PageKsm(page)))
942                 return false;
943         count = page_trans_huge_mapcount(page, total_mapcount);
944         if (count <= 1 && PageSwapCache(page)) {
945                 count += page_swapcount(page);
946                 if (count == 1 && !PageWriteback(page)) {
947                         delete_from_swap_cache(page);
948                         SetPageDirty(page);
949                 }
950         }
951         return count <= 1;
952 }
953
954 /*
955  * If swap is getting full, or if there are no more mappings of this page,
956  * then try_to_free_swap is called to free its swap space.
957  */
958 int try_to_free_swap(struct page *page)
959 {
960         VM_BUG_ON_PAGE(!PageLocked(page), page);
961
962         if (!PageSwapCache(page))
963                 return 0;
964         if (PageWriteback(page))
965                 return 0;
966         if (page_swapcount(page))
967                 return 0;
968
969         /*
970          * Once hibernation has begun to create its image of memory,
971          * there's a danger that one of the calls to try_to_free_swap()
972          * - most probably a call from __try_to_reclaim_swap() while
973          * hibernation is allocating its own swap pages for the image,
974          * but conceivably even a call from memory reclaim - will free
975          * the swap from a page which has already been recorded in the
976          * image as a clean swapcache page, and then reuse its swap for
977          * another page of the image.  On waking from hibernation, the
978          * original page might be freed under memory pressure, then
979          * later read back in from swap, now with the wrong data.
980          *
981          * Hibernation suspends storage while it is writing the image
982          * to disk so check that here.
983          */
984         if (pm_suspended_storage())
985                 return 0;
986
987         delete_from_swap_cache(page);
988         SetPageDirty(page);
989         return 1;
990 }
991
992 /*
993  * Free the swap entry like above, but also try to
994  * free the page cache entry if it is the last user.
995  */
996 int free_swap_and_cache(swp_entry_t entry)
997 {
998         struct swap_info_struct *p;
999         struct page *page = NULL;
1000
1001         if (non_swap_entry(entry))
1002                 return 1;
1003
1004         p = swap_info_get(entry);
1005         if (p) {
1006                 if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
1007                         page = find_get_page(swap_address_space(entry),
1008                                              swp_offset(entry));
1009                         if (page && !trylock_page(page)) {
1010                                 put_page(page);
1011                                 page = NULL;
1012                         }
1013                 }
1014                 spin_unlock(&p->lock);
1015         }
1016         if (page) {
1017                 /*
1018                  * Not mapped elsewhere, or swap space full? Free it!
1019                  * Also recheck PageSwapCache now page is locked (above).
1020                  */
1021                 if (PageSwapCache(page) && !PageWriteback(page) &&
1022                     (!page_mapped(page) || mem_cgroup_swap_full(page))) {
1023                         delete_from_swap_cache(page);
1024                         SetPageDirty(page);
1025                 }
1026                 unlock_page(page);
1027                 put_page(page);
1028         }
1029         return p != NULL;
1030 }
1031
1032 #ifdef CONFIG_HIBERNATION
1033 /*
1034  * Find the swap type that corresponds to given device (if any).
1035  *
1036  * @offset - number of the PAGE_SIZE-sized block of the device, starting
1037  * from 0, in which the swap header is expected to be located.
1038  *
1039  * This is needed for the suspend to disk (aka swsusp).
1040  */
1041 int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
1042 {
1043         struct block_device *bdev = NULL;
1044         int type;
1045
1046         if (device)
1047                 bdev = bdget(device);
1048
1049         spin_lock(&swap_lock);
1050         for (type = 0; type < nr_swapfiles; type++) {
1051                 struct swap_info_struct *sis = swap_info[type];
1052
1053                 if (!(sis->flags & SWP_WRITEOK))
1054                         continue;
1055
1056                 if (!bdev) {
1057                         if (bdev_p)
1058                                 *bdev_p = bdgrab(sis->bdev);
1059
1060                         spin_unlock(&swap_lock);
1061                         return type;
1062                 }
1063                 if (bdev == sis->bdev) {
1064                         struct swap_extent *se = &sis->first_swap_extent;
1065
1066                         if (se->start_block == offset) {
1067                                 if (bdev_p)
1068                                         *bdev_p = bdgrab(sis->bdev);
1069
1070                                 spin_unlock(&swap_lock);
1071                                 bdput(bdev);
1072                                 return type;
1073                         }
1074                 }
1075         }
1076         spin_unlock(&swap_lock);
1077         if (bdev)
1078                 bdput(bdev);
1079
1080         return -ENODEV;
1081 }
1082
1083 /*
1084  * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
1085  * corresponding to given index in swap_info (swap type).
1086  */
1087 sector_t swapdev_block(int type, pgoff_t offset)
1088 {
1089         struct block_device *bdev;
1090
1091         if ((unsigned int)type >= nr_swapfiles)
1092                 return 0;
1093         if (!(swap_info[type]->flags & SWP_WRITEOK))
1094                 return 0;
1095         return map_swap_entry(swp_entry(type, offset), &bdev);
1096 }
1097
1098 /*
1099  * Return either the total number of swap pages of given type, or the number
1100  * of free pages of that type (depending on @free)
1101  *
1102  * This is needed for software suspend
1103  */
1104 unsigned int count_swap_pages(int type, int free)
1105 {
1106         unsigned int n = 0;
1107
1108         spin_lock(&swap_lock);
1109         if ((unsigned int)type < nr_swapfiles) {
1110                 struct swap_info_struct *sis = swap_info[type];
1111
1112                 spin_lock(&sis->lock);
1113                 if (sis->flags & SWP_WRITEOK) {
1114                         n = sis->pages;
1115                         if (free)
1116                                 n -= sis->inuse_pages;
1117                 }
1118                 spin_unlock(&sis->lock);
1119         }
1120         spin_unlock(&swap_lock);
1121         return n;
1122 }
1123 #endif /* CONFIG_HIBERNATION */
1124
1125 static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)
1126 {
1127         return pte_same(pte_swp_clear_soft_dirty(pte), swp_pte);
1128 }
1129
1130 /*
1131  * No need to decide whether this PTE shares the swap entry with others,
1132  * just let do_wp_page work it out if a write is requested later - to
1133  * force COW, vm_page_prot omits write permission from any private vma.
1134  */
1135 static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
1136                 unsigned long addr, swp_entry_t entry, struct page *page)
1137 {
1138         struct page *swapcache;
1139         struct mem_cgroup *memcg;
1140         spinlock_t *ptl;
1141         pte_t *pte;
1142         int ret = 1;
1143
1144         swapcache = page;
1145         page = ksm_might_need_to_copy(page, vma, addr);
1146         if (unlikely(!page))
1147                 return -ENOMEM;
1148
1149         if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL,
1150                                 &memcg, false)) {
1151                 ret = -ENOMEM;
1152                 goto out_nolock;
1153         }
1154
1155         pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
1156         if (unlikely(!pte_same_as_swp(*pte, swp_entry_to_pte(entry)))) {
1157                 mem_cgroup_cancel_charge(page, memcg, false);
1158                 ret = 0;
1159                 goto out;
1160         }
1161
1162         dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
1163         inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
1164         get_page(page);
1165         set_pte_at(vma->vm_mm, addr, pte,
1166                    pte_mkold(mk_pte(page, vma->vm_page_prot)));
1167         if (page == swapcache) {
1168                 page_add_anon_rmap(page, vma, addr, false);
1169                 mem_cgroup_commit_charge(page, memcg, true, false);
1170         } else { /* ksm created a completely new copy */
1171                 page_add_new_anon_rmap(page, vma, addr, false);
1172                 mem_cgroup_commit_charge(page, memcg, false, false);
1173                 lru_cache_add_active_or_unevictable(page, vma);
1174         }
1175         swap_free(entry);
1176         /*
1177          * Move the page to the active list so it is not
1178          * immediately swapped out again after swapon.
1179          */
1180         activate_page(page);
1181 out:
1182         pte_unmap_unlock(pte, ptl);
1183 out_nolock:
1184         if (page != swapcache) {
1185                 unlock_page(page);
1186                 put_page(page);
1187         }
1188         return ret;
1189 }
1190
1191 static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
1192                                 unsigned long addr, unsigned long end,
1193                                 swp_entry_t entry, struct page *page)
1194 {
1195         pte_t swp_pte = swp_entry_to_pte(entry);
1196         pte_t *pte;
1197         int ret = 0;
1198
1199         /*
1200          * We don't actually need pte lock while scanning for swp_pte: since
1201          * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
1202          * page table while we're scanning; though it could get zapped, and on
1203          * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
1204          * of unmatched parts which look like swp_pte, so unuse_pte must
1205          * recheck under pte lock.  Scanning without pte lock lets it be
1206          * preemptable whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
1207          */
1208         pte = pte_offset_map(pmd, addr);
1209         do {
1210                 /*
1211                  * swapoff spends a _lot_ of time in this loop!
1212                  * Test inline before going to call unuse_pte.
1213                  */
1214                 if (unlikely(pte_same_as_swp(*pte, swp_pte))) {
1215                         pte_unmap(pte);
1216                         ret = unuse_pte(vma, pmd, addr, entry, page);
1217                         if (ret)
1218                                 goto out;
1219                         pte = pte_offset_map(pmd, addr);
1220                 }
1221         } while (pte++, addr += PAGE_SIZE, addr != end);
1222         pte_unmap(pte - 1);
1223 out:
1224         return ret;
1225 }
1226
1227 static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
1228                                 unsigned long addr, unsigned long end,
1229                                 swp_entry_t entry, struct page *page)
1230 {
1231         pmd_t *pmd;
1232         unsigned long next;
1233         int ret;
1234
1235         pmd = pmd_offset(pud, addr);
1236         do {
1237                 next = pmd_addr_end(addr, end);
1238                 if (pmd_none_or_trans_huge_or_clear_bad(pmd))
1239                         continue;
1240                 ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
1241                 if (ret)
1242                         return ret;
1243         } while (pmd++, addr = next, addr != end);
1244         return 0;
1245 }
1246
1247 static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
1248                                 unsigned long addr, unsigned long end,
1249                                 swp_entry_t entry, struct page *page)
1250 {
1251         pud_t *pud;
1252         unsigned long next;
1253         int ret;
1254
1255         pud = pud_offset(pgd, addr);
1256         do {
1257                 next = pud_addr_end(addr, end);
1258                 if (pud_none_or_clear_bad(pud))
1259                         continue;
1260                 ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
1261                 if (ret)
1262                         return ret;
1263         } while (pud++, addr = next, addr != end);
1264         return 0;
1265 }
1266
1267 static int unuse_vma(struct vm_area_struct *vma,
1268                                 swp_entry_t entry, struct page *page)
1269 {
1270         pgd_t *pgd;
1271         unsigned long addr, end, next;
1272         int ret;
1273
1274         if (page_anon_vma(page)) {
1275                 addr = page_address_in_vma(page, vma);
1276                 if (addr == -EFAULT)
1277                         return 0;
1278                 else
1279                         end = addr + PAGE_SIZE;
1280         } else {
1281                 addr = vma->vm_start;
1282                 end = vma->vm_end;
1283         }
1284
1285         pgd = pgd_offset(vma->vm_mm, addr);
1286         do {
1287                 next = pgd_addr_end(addr, end);
1288                 if (pgd_none_or_clear_bad(pgd))
1289                         continue;
1290                 ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
1291                 if (ret)
1292                         return ret;
1293         } while (pgd++, addr = next, addr != end);
1294         return 0;
1295 }
1296
1297 static int unuse_mm(struct mm_struct *mm,
1298                                 swp_entry_t entry, struct page *page)
1299 {
1300         struct vm_area_struct *vma;
1301         int ret = 0;
1302
1303         if (!down_read_trylock(&mm->mmap_sem)) {
1304                 /*
1305                  * Activate page so shrink_inactive_list is unlikely to unmap
1306                  * its ptes while lock is dropped, so swapoff can make progress.
1307                  */
1308                 activate_page(page);
1309                 unlock_page(page);
1310                 down_read(&mm->mmap_sem);
1311                 lock_page(page);
1312         }
1313         for (vma = mm->mmap; vma; vma = vma->vm_next) {
1314                 if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1315                         break;
1316         }
1317         up_read(&mm->mmap_sem);
1318         return (ret < 0)? ret: 0;
1319 }
1320
1321 /*
1322  * Scan swap_map (or frontswap_map if frontswap parameter is true)
1323  * from current position to next entry still in use.
1324  * Recycle to start on reaching the end, returning 0 when empty.
1325  */
1326 static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1327                                         unsigned int prev, bool frontswap)
1328 {
1329         unsigned int max = si->max;
1330         unsigned int i = prev;
1331         unsigned char count;
1332
1333         /*
1334          * No need for swap_lock here: we're just looking
1335          * for whether an entry is in use, not modifying it; false
1336          * hits are okay, and sys_swapoff() has already prevented new
1337          * allocations from this area (while holding swap_lock).
1338          */
1339         for (;;) {
1340                 if (++i >= max) {
1341                         if (!prev) {
1342                                 i = 0;
1343                                 break;
1344                         }
1345                         /*
1346                          * No entries in use at top of swap_map,
1347                          * loop back to start and recheck there.
1348                          */
1349                         max = prev + 1;
1350                         prev = 0;
1351                         i = 1;
1352                 }
1353                 if (frontswap) {
1354                         if (frontswap_test(si, i))
1355                                 break;
1356                         else
1357                                 continue;
1358                 }
1359                 count = READ_ONCE(si->swap_map[i]);
1360                 if (count && swap_count(count) != SWAP_MAP_BAD)
1361                         break;
1362         }
1363         return i;
1364 }
1365
1366 /*
1367  * We completely avoid races by reading each swap page in advance,
1368  * and then search for the process using it.  All the necessary
1369  * page table adjustments can then be made atomically.
1370  *
1371  * if the boolean frontswap is true, only unuse pages_to_unuse pages;
1372  * pages_to_unuse==0 means all pages; ignored if frontswap is false
1373  */
1374 int try_to_unuse(unsigned int type, bool frontswap,
1375                  unsigned long pages_to_unuse)
1376 {
1377         struct swap_info_struct *si = swap_info[type];
1378         struct mm_struct *start_mm;
1379         volatile unsigned char *swap_map; /* swap_map is accessed without
1380                                            * locking. Mark it as volatile
1381                                            * to prevent compiler doing
1382                                            * something odd.
1383                                            */
1384         unsigned char swcount;
1385         struct page *page;
1386         swp_entry_t entry;
1387         unsigned int i = 0;
1388         int retval = 0;
1389
1390         /*
1391          * When searching mms for an entry, a good strategy is to
1392          * start at the first mm we freed the previous entry from
1393          * (though actually we don't notice whether we or coincidence
1394          * freed the entry).  Initialize this start_mm with a hold.
1395          *
1396          * A simpler strategy would be to start at the last mm we
1397          * freed the previous entry from; but that would take less
1398          * advantage of mmlist ordering, which clusters forked mms
1399          * together, child after parent.  If we race with dup_mmap(), we
1400          * prefer to resolve parent before child, lest we miss entries
1401          * duplicated after we scanned child: using last mm would invert
1402          * that.
1403          */
1404         start_mm = &init_mm;
1405         atomic_inc(&init_mm.mm_users);
1406
1407         /*
1408          * Keep on scanning until all entries have gone.  Usually,
1409          * one pass through swap_map is enough, but not necessarily:
1410          * there are races when an instance of an entry might be missed.
1411          */
1412         while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
1413                 if (signal_pending(current)) {
1414                         retval = -EINTR;
1415                         break;
1416                 }
1417
1418                 /*
1419                  * Get a page for the entry, using the existing swap
1420                  * cache page if there is one.  Otherwise, get a clean
1421                  * page and read the swap into it.
1422                  */
1423                 swap_map = &si->swap_map[i];
1424                 entry = swp_entry(type, i);
1425                 page = read_swap_cache_async(entry,
1426                                         GFP_HIGHUSER_MOVABLE, NULL, 0);
1427                 if (!page) {
1428                         /*
1429                          * Either swap_duplicate() failed because entry
1430                          * has been freed independently, and will not be
1431                          * reused since sys_swapoff() already disabled
1432                          * allocation from here, or alloc_page() failed.
1433                          */
1434                         swcount = *swap_map;
1435                         /*
1436                          * We don't hold lock here, so the swap entry could be
1437                          * SWAP_MAP_BAD (when the cluster is discarding).
1438                          * Instead of fail out, We can just skip the swap
1439                          * entry because swapoff will wait for discarding
1440                          * finish anyway.
1441                          */
1442                         if (!swcount || swcount == SWAP_MAP_BAD)
1443                                 continue;
1444                         retval = -ENOMEM;
1445                         break;
1446                 }
1447
1448                 /*
1449                  * Don't hold on to start_mm if it looks like exiting.
1450                  */
1451                 if (atomic_read(&start_mm->mm_users) == 1) {
1452                         mmput(start_mm);
1453                         start_mm = &init_mm;
1454                         atomic_inc(&init_mm.mm_users);
1455                 }
1456
1457                 /*
1458                  * Wait for and lock page.  When do_swap_page races with
1459                  * try_to_unuse, do_swap_page can handle the fault much
1460                  * faster than try_to_unuse can locate the entry.  This
1461                  * apparently redundant "wait_on_page_locked" lets try_to_unuse
1462                  * defer to do_swap_page in such a case - in some tests,
1463                  * do_swap_page and try_to_unuse repeatedly compete.
1464                  */
1465                 wait_on_page_locked(page);
1466                 wait_on_page_writeback(page);
1467                 lock_page(page);
1468                 wait_on_page_writeback(page);
1469
1470                 /*
1471                  * Remove all references to entry.
1472                  */
1473                 swcount = *swap_map;
1474                 if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1475                         retval = shmem_unuse(entry, page);
1476                         /* page has already been unlocked and released */
1477                         if (retval < 0)
1478                                 break;
1479                         continue;
1480                 }
1481                 if (swap_count(swcount) && start_mm != &init_mm)
1482                         retval = unuse_mm(start_mm, entry, page);
1483
1484                 if (swap_count(*swap_map)) {
1485                         int set_start_mm = (*swap_map >= swcount);
1486                         struct list_head *p = &start_mm->mmlist;
1487                         struct mm_struct *new_start_mm = start_mm;
1488                         struct mm_struct *prev_mm = start_mm;
1489                         struct mm_struct *mm;
1490
1491                         atomic_inc(&new_start_mm->mm_users);
1492                         atomic_inc(&prev_mm->mm_users);
1493                         spin_lock(&mmlist_lock);
1494                         while (swap_count(*swap_map) && !retval &&
1495                                         (p = p->next) != &start_mm->mmlist) {
1496                                 mm = list_entry(p, struct mm_struct, mmlist);
1497                                 if (!atomic_inc_not_zero(&mm->mm_users))
1498                                         continue;
1499                                 spin_unlock(&mmlist_lock);
1500                                 mmput(prev_mm);
1501                                 prev_mm = mm;
1502
1503                                 cond_resched();
1504
1505                                 swcount = *swap_map;
1506                                 if (!swap_count(swcount)) /* any usage ? */
1507                                         ;
1508                                 else if (mm == &init_mm)
1509                                         set_start_mm = 1;
1510                                 else
1511                                         retval = unuse_mm(mm, entry, page);
1512
1513                                 if (set_start_mm && *swap_map < swcount) {
1514                                         mmput(new_start_mm);
1515                                         atomic_inc(&mm->mm_users);
1516                                         new_start_mm = mm;
1517                                         set_start_mm = 0;
1518                                 }
1519                                 spin_lock(&mmlist_lock);
1520                         }
1521                         spin_unlock(&mmlist_lock);
1522                         mmput(prev_mm);
1523                         mmput(start_mm);
1524                         start_mm = new_start_mm;
1525                 }
1526                 if (retval) {
1527                         unlock_page(page);
1528                         put_page(page);
1529                         break;
1530                 }
1531
1532                 /*
1533                  * If a reference remains (rare), we would like to leave
1534                  * the page in the swap cache; but try_to_unmap could
1535                  * then re-duplicate the entry once we drop page lock,
1536                  * so we might loop indefinitely; also, that page could
1537                  * not be swapped out to other storage meanwhile.  So:
1538                  * delete from cache even if there's another reference,
1539                  * after ensuring that the data has been saved to disk -
1540                  * since if the reference remains (rarer), it will be
1541                  * read from disk into another page.  Splitting into two
1542                  * pages would be incorrect if swap supported "shared
1543                  * private" pages, but they are handled by tmpfs files.
1544                  *
1545                  * Given how unuse_vma() targets one particular offset
1546                  * in an anon_vma, once the anon_vma has been determined,
1547                  * this splitting happens to be just what is needed to
1548                  * handle where KSM pages have been swapped out: re-reading
1549                  * is unnecessarily slow, but we can fix that later on.
1550                  */
1551                 if (swap_count(*swap_map) &&
1552                      PageDirty(page) && PageSwapCache(page)) {
1553                         struct writeback_control wbc = {
1554                                 .sync_mode = WB_SYNC_NONE,
1555                         };
1556
1557                         swap_writepage(page, &wbc);
1558                         lock_page(page);
1559                         wait_on_page_writeback(page);
1560                 }
1561
1562                 /*
1563                  * It is conceivable that a racing task removed this page from
1564                  * swap cache just before we acquired the page lock at the top,
1565                  * or while we dropped it in unuse_mm().  The page might even
1566                  * be back in swap cache on another swap area: that we must not
1567                  * delete, since it may not have been written out to swap yet.
1568                  */
1569                 if (PageSwapCache(page) &&
1570                     likely(page_private(page) == entry.val))
1571                         delete_from_swap_cache(page);
1572
1573                 /*
1574                  * So we could skip searching mms once swap count went
1575                  * to 1, we did not mark any present ptes as dirty: must
1576                  * mark page dirty so shrink_page_list will preserve it.
1577                  */
1578                 SetPageDirty(page);
1579                 unlock_page(page);
1580                 put_page(page);
1581
1582                 /*
1583                  * Make sure that we aren't completely killing
1584                  * interactive performance.
1585                  */
1586                 cond_resched();
1587                 if (frontswap && pages_to_unuse > 0) {
1588                         if (!--pages_to_unuse)
1589                                 break;
1590                 }
1591         }
1592
1593         mmput(start_mm);
1594         return retval;
1595 }
1596
1597 /*
1598  * After a successful try_to_unuse, if no swap is now in use, we know
1599  * we can empty the mmlist.  swap_lock must be held on entry and exit.
1600  * Note that mmlist_lock nests inside swap_lock, and an mm must be
1601  * added to the mmlist just after page_duplicate - before would be racy.
1602  */
1603 static void drain_mmlist(void)
1604 {
1605         struct list_head *p, *next;
1606         unsigned int type;
1607
1608         for (type = 0; type < nr_swapfiles; type++)
1609                 if (swap_info[type]->inuse_pages)
1610                         return;
1611         spin_lock(&mmlist_lock);
1612         list_for_each_safe(p, next, &init_mm.mmlist)
1613                 list_del_init(p);
1614         spin_unlock(&mmlist_lock);
1615 }
1616
1617 /*
1618  * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1619  * corresponds to page offset for the specified swap entry.
1620  * Note that the type of this function is sector_t, but it returns page offset
1621  * into the bdev, not sector offset.
1622  */
1623 static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1624 {
1625         struct swap_info_struct *sis;
1626         struct swap_extent *start_se;
1627         struct swap_extent *se;
1628         pgoff_t offset;
1629
1630         sis = swap_info[swp_type(entry)];
1631         *bdev = sis->bdev;
1632
1633         offset = swp_offset(entry);
1634         start_se = sis->curr_swap_extent;
1635         se = start_se;
1636
1637         for ( ; ; ) {
1638                 if (se->start_page <= offset &&
1639                                 offset < (se->start_page + se->nr_pages)) {
1640                         return se->start_block + (offset - se->start_page);
1641                 }
1642                 se = list_next_entry(se, list);
1643                 sis->curr_swap_extent = se;
1644                 BUG_ON(se == start_se);         /* It *must* be present */
1645         }
1646 }
1647
1648 /*
1649  * Returns the page offset into bdev for the specified page's swap entry.
1650  */
1651 sector_t map_swap_page(struct page *page, struct block_device **bdev)
1652 {
1653         swp_entry_t entry;
1654         entry.val = page_private(page);
1655         return map_swap_entry(entry, bdev);
1656 }
1657
1658 /*
1659  * Free all of a swapdev's extent information
1660  */
1661 static void destroy_swap_extents(struct swap_info_struct *sis)
1662 {
1663         while (!list_empty(&sis->first_swap_extent.list)) {
1664                 struct swap_extent *se;
1665
1666                 se = list_first_entry(&sis->first_swap_extent.list,
1667                                 struct swap_extent, list);
1668                 list_del(&se->list);
1669                 kfree(se);
1670         }
1671
1672         if (sis->flags & SWP_FILE) {
1673                 struct file *swap_file = sis->swap_file;
1674                 struct address_space *mapping = swap_file->f_mapping;
1675
1676                 sis->flags &= ~SWP_FILE;
1677                 mapping->a_ops->swap_deactivate(swap_file);
1678         }
1679 }
1680
1681 /*
1682  * Add a block range (and the corresponding page range) into this swapdev's
1683  * extent list.  The extent list is kept sorted in page order.
1684  *
1685  * This function rather assumes that it is called in ascending page order.
1686  */
1687 int
1688 add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1689                 unsigned long nr_pages, sector_t start_block)
1690 {
1691         struct swap_extent *se;
1692         struct swap_extent *new_se;
1693         struct list_head *lh;
1694
1695         if (start_page == 0) {
1696                 se = &sis->first_swap_extent;
1697                 sis->curr_swap_extent = se;
1698                 se->start_page = 0;
1699                 se->nr_pages = nr_pages;
1700                 se->start_block = start_block;
1701                 return 1;
1702         } else {
1703                 lh = sis->first_swap_extent.list.prev;  /* Highest extent */
1704                 se = list_entry(lh, struct swap_extent, list);
1705                 BUG_ON(se->start_page + se->nr_pages != start_page);
1706                 if (se->start_block + se->nr_pages == start_block) {
1707                         /* Merge it */
1708                         se->nr_pages += nr_pages;
1709                         return 0;
1710                 }
1711         }
1712
1713         /*
1714          * No merge.  Insert a new extent, preserving ordering.
1715          */
1716         new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1717         if (new_se == NULL)
1718                 return -ENOMEM;
1719         new_se->start_page = start_page;
1720         new_se->nr_pages = nr_pages;
1721         new_se->start_block = start_block;
1722
1723         list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1724         return 1;
1725 }
1726
1727 /*
1728  * A `swap extent' is a simple thing which maps a contiguous range of pages
1729  * onto a contiguous range of disk blocks.  An ordered list of swap extents
1730  * is built at swapon time and is then used at swap_writepage/swap_readpage
1731  * time for locating where on disk a page belongs.
1732  *
1733  * If the swapfile is an S_ISBLK block device, a single extent is installed.
1734  * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1735  * swap files identically.
1736  *
1737  * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1738  * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
1739  * swapfiles are handled *identically* after swapon time.
1740  *
1741  * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1742  * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
1743  * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1744  * requirements, they are simply tossed out - we will never use those blocks
1745  * for swapping.
1746  *
1747  * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
1748  * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1749  * which will scribble on the fs.
1750  *
1751  * The amount of disk space which a single swap extent represents varies.
1752  * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
1753  * extents in the list.  To avoid much list walking, we cache the previous
1754  * search location in `curr_swap_extent', and start new searches from there.
1755  * This is extremely effective.  The average number of iterations in
1756  * map_swap_page() has been measured at about 0.3 per page.  - akpm.
1757  */
1758 static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1759 {
1760         struct file *swap_file = sis->swap_file;
1761         struct address_space *mapping = swap_file->f_mapping;
1762         struct inode *inode = mapping->host;
1763         int ret;
1764
1765         if (S_ISBLK(inode->i_mode)) {
1766                 ret = add_swap_extent(sis, 0, sis->max, 0);
1767                 *span = sis->pages;
1768                 return ret;
1769         }
1770
1771         if (mapping->a_ops->swap_activate) {
1772                 ret = mapping->a_ops->swap_activate(sis, swap_file, span);
1773                 if (!ret) {
1774                         sis->flags |= SWP_FILE;
1775                         ret = add_swap_extent(sis, 0, sis->max, 0);
1776                         *span = sis->pages;
1777                 }
1778                 return ret;
1779         }
1780
1781         return generic_swapfile_activate(sis, swap_file, span);
1782 }
1783
1784 static void _enable_swap_info(struct swap_info_struct *p, int prio,
1785                                 unsigned char *swap_map,
1786                                 struct swap_cluster_info *cluster_info)
1787 {
1788         if (prio >= 0)
1789                 p->prio = prio;
1790         else
1791                 p->prio = --least_priority;
1792         /*
1793          * the plist prio is negated because plist ordering is
1794          * low-to-high, while swap ordering is high-to-low
1795          */
1796         p->list.prio = -p->prio;
1797         p->avail_list.prio = -p->prio;
1798         p->swap_map = swap_map;
1799         p->cluster_info = cluster_info;
1800         p->flags |= SWP_WRITEOK;
1801         atomic_long_add(p->pages, &nr_swap_pages);
1802         total_swap_pages += p->pages;
1803
1804         assert_spin_locked(&swap_lock);
1805         /*
1806          * both lists are plists, and thus priority ordered.
1807          * swap_active_head needs to be priority ordered for swapoff(),
1808          * which on removal of any swap_info_struct with an auto-assigned
1809          * (i.e. negative) priority increments the auto-assigned priority
1810          * of any lower-priority swap_info_structs.
1811          * swap_avail_head needs to be priority ordered for get_swap_page(),
1812          * which allocates swap pages from the highest available priority
1813          * swap_info_struct.
1814          */
1815         plist_add(&p->list, &swap_active_head);
1816         spin_lock(&swap_avail_lock);
1817         plist_add(&p->avail_list, &swap_avail_head);
1818         spin_unlock(&swap_avail_lock);
1819 }
1820
1821 static void enable_swap_info(struct swap_info_struct *p, int prio,
1822                                 unsigned char *swap_map,
1823                                 struct swap_cluster_info *cluster_info,
1824                                 unsigned long *frontswap_map)
1825 {
1826         frontswap_init(p->type, frontswap_map);
1827         spin_lock(&swap_lock);
1828         spin_lock(&p->lock);
1829          _enable_swap_info(p, prio, swap_map, cluster_info);
1830         spin_unlock(&p->lock);
1831         spin_unlock(&swap_lock);
1832 }
1833
1834 static void reinsert_swap_info(struct swap_info_struct *p)
1835 {
1836         spin_lock(&swap_lock);
1837         spin_lock(&p->lock);
1838         _enable_swap_info(p, p->prio, p->swap_map, p->cluster_info);
1839         spin_unlock(&p->lock);
1840         spin_unlock(&swap_lock);
1841 }
1842
1843 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1844 {
1845         struct swap_info_struct *p = NULL;
1846         unsigned char *swap_map;
1847         struct swap_cluster_info *cluster_info;
1848         unsigned long *frontswap_map;
1849         struct file *swap_file, *victim;
1850         struct address_space *mapping;
1851         struct inode *inode;
1852         struct filename *pathname;
1853         int err, found = 0;
1854         unsigned int old_block_size;
1855
1856         if (!capable(CAP_SYS_ADMIN))
1857                 return -EPERM;
1858
1859         BUG_ON(!current->mm);
1860
1861         pathname = getname(specialfile);
1862         if (IS_ERR(pathname))
1863                 return PTR_ERR(pathname);
1864
1865         victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
1866         err = PTR_ERR(victim);
1867         if (IS_ERR(victim))
1868                 goto out;
1869
1870         mapping = victim->f_mapping;
1871         spin_lock(&swap_lock);
1872         plist_for_each_entry(p, &swap_active_head, list) {
1873                 if (p->flags & SWP_WRITEOK) {
1874                         if (p->swap_file->f_mapping == mapping) {
1875                                 found = 1;
1876                                 break;
1877                         }
1878                 }
1879         }
1880         if (!found) {
1881                 err = -EINVAL;
1882                 spin_unlock(&swap_lock);
1883                 goto out_dput;
1884         }
1885         if (!security_vm_enough_memory_mm(current->mm, p->pages))
1886                 vm_unacct_memory(p->pages);
1887         else {
1888                 err = -ENOMEM;
1889                 spin_unlock(&swap_lock);
1890                 goto out_dput;
1891         }
1892         spin_lock(&swap_avail_lock);
1893         plist_del(&p->avail_list, &swap_avail_head);
1894         spin_unlock(&swap_avail_lock);
1895         spin_lock(&p->lock);
1896         if (p->prio < 0) {
1897                 struct swap_info_struct *si = p;
1898
1899                 plist_for_each_entry_continue(si, &swap_active_head, list) {
1900                         si->prio++;
1901                         si->list.prio--;
1902                         si->avail_list.prio--;
1903                 }
1904                 least_priority++;
1905         }
1906         plist_del(&p->list, &swap_active_head);
1907         atomic_long_sub(p->pages, &nr_swap_pages);
1908         total_swap_pages -= p->pages;
1909         p->flags &= ~SWP_WRITEOK;
1910         spin_unlock(&p->lock);
1911         spin_unlock(&swap_lock);
1912
1913         set_current_oom_origin();
1914         err = try_to_unuse(p->type, false, 0); /* force unuse all pages */
1915         clear_current_oom_origin();
1916
1917         if (err) {
1918                 /* re-insert swap space back into swap_list */
1919                 reinsert_swap_info(p);
1920                 goto out_dput;
1921         }
1922
1923         flush_work(&p->discard_work);
1924
1925         destroy_swap_extents(p);
1926         if (p->flags & SWP_CONTINUED)
1927                 free_swap_count_continuations(p);
1928
1929         mutex_lock(&swapon_mutex);
1930         spin_lock(&swap_lock);
1931         spin_lock(&p->lock);
1932         drain_mmlist();
1933
1934         /* wait for anyone still in scan_swap_map */
1935         p->highest_bit = 0;             /* cuts scans short */
1936         while (p->flags >= SWP_SCANNING) {
1937                 spin_unlock(&p->lock);
1938                 spin_unlock(&swap_lock);
1939                 schedule_timeout_uninterruptible(1);
1940                 spin_lock(&swap_lock);
1941                 spin_lock(&p->lock);
1942         }
1943
1944         swap_file = p->swap_file;
1945         old_block_size = p->old_block_size;
1946         p->swap_file = NULL;
1947         p->max = 0;
1948         swap_map = p->swap_map;
1949         p->swap_map = NULL;
1950         cluster_info = p->cluster_info;
1951         p->cluster_info = NULL;
1952         frontswap_map = frontswap_map_get(p);
1953         spin_unlock(&p->lock);
1954         spin_unlock(&swap_lock);
1955         frontswap_invalidate_area(p->type);
1956         frontswap_map_set(p, NULL);
1957         mutex_unlock(&swapon_mutex);
1958         free_percpu(p->percpu_cluster);
1959         p->percpu_cluster = NULL;
1960         vfree(swap_map);
1961         vfree(cluster_info);
1962         vfree(frontswap_map);
1963         /* Destroy swap account information */
1964         swap_cgroup_swapoff(p->type);
1965
1966         inode = mapping->host;
1967         if (S_ISBLK(inode->i_mode)) {
1968                 struct block_device *bdev = I_BDEV(inode);
1969                 set_blocksize(bdev, old_block_size);
1970                 blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
1971         } else {
1972                 inode_lock(inode);
1973                 inode->i_flags &= ~S_SWAPFILE;
1974                 inode_unlock(inode);
1975         }
1976         filp_close(swap_file, NULL);
1977
1978         /*
1979          * Clear the SWP_USED flag after all resources are freed so that swapon
1980          * can reuse this swap_info in alloc_swap_info() safely.  It is ok to
1981          * not hold p->lock after we cleared its SWP_WRITEOK.
1982          */
1983         spin_lock(&swap_lock);
1984         p->flags = 0;
1985         spin_unlock(&swap_lock);
1986
1987         err = 0;
1988         atomic_inc(&proc_poll_event);
1989         wake_up_interruptible(&proc_poll_wait);
1990
1991 out_dput:
1992         filp_close(victim, NULL);
1993 out:
1994         putname(pathname);
1995         return err;
1996 }
1997
1998 #ifdef CONFIG_PROC_FS
1999 static unsigned swaps_poll(struct file *file, poll_table *wait)
2000 {
2001         struct seq_file *seq = file->private_data;
2002
2003         poll_wait(file, &proc_poll_wait, wait);
2004
2005         if (seq->poll_event != atomic_read(&proc_poll_event)) {
2006                 seq->poll_event = atomic_read(&proc_poll_event);
2007                 return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
2008         }
2009
2010         return POLLIN | POLLRDNORM;
2011 }
2012
2013 /* iterator */
2014 static void *swap_start(struct seq_file *swap, loff_t *pos)
2015 {
2016         struct swap_info_struct *si;
2017         int type;
2018         loff_t l = *pos;
2019
2020         mutex_lock(&swapon_mutex);
2021
2022         if (!l)
2023                 return SEQ_START_TOKEN;
2024
2025         for (type = 0; type < nr_swapfiles; type++) {
2026                 smp_rmb();      /* read nr_swapfiles before swap_info[type] */
2027                 si = swap_info[type];
2028                 if (!(si->flags & SWP_USED) || !si->swap_map)
2029                         continue;
2030                 if (!--l)
2031                         return si;
2032         }
2033
2034         return NULL;
2035 }
2036
2037 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
2038 {
2039         struct swap_info_struct *si = v;
2040         int type;
2041
2042         if (v == SEQ_START_TOKEN)
2043                 type = 0;
2044         else
2045                 type = si->type + 1;
2046
2047         for (; type < nr_swapfiles; type++) {
2048                 smp_rmb();      /* read nr_swapfiles before swap_info[type] */
2049                 si = swap_info[type];
2050                 if (!(si->flags & SWP_USED) || !si->swap_map)
2051                         continue;
2052                 ++*pos;
2053                 return si;
2054         }
2055
2056         return NULL;
2057 }
2058
2059 static void swap_stop(struct seq_file *swap, void *v)
2060 {
2061         mutex_unlock(&swapon_mutex);
2062 }
2063
2064 static int swap_show(struct seq_file *swap, void *v)
2065 {
2066         struct swap_info_struct *si = v;
2067         struct file *file;
2068         int len;
2069
2070         if (si == SEQ_START_TOKEN) {
2071                 seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
2072                 return 0;
2073         }
2074
2075         file = si->swap_file;
2076         len = seq_file_path(swap, file, " \t\n\\");
2077         seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
2078                         len < 40 ? 40 - len : 1, " ",
2079                         S_ISBLK(file_inode(file)->i_mode) ?
2080                                 "partition" : "file\t",
2081                         si->pages << (PAGE_SHIFT - 10),
2082                         si->inuse_pages << (PAGE_SHIFT - 10),
2083                         si->prio);
2084         return 0;
2085 }
2086
2087 static const struct seq_operations swaps_op = {
2088         .start =        swap_start,
2089         .next =         swap_next,
2090         .stop =         swap_stop,
2091         .show =         swap_show
2092 };
2093
2094 static int swaps_open(struct inode *inode, struct file *file)
2095 {
2096         struct seq_file *seq;
2097         int ret;
2098
2099         ret = seq_open(file, &swaps_op);
2100         if (ret)
2101                 return ret;
2102
2103         seq = file->private_data;
2104         seq->poll_event = atomic_read(&proc_poll_event);
2105         return 0;
2106 }
2107
2108 static const struct file_operations proc_swaps_operations = {
2109         .open           = swaps_open,
2110         .read           = seq_read,
2111         .llseek         = seq_lseek,
2112         .release        = seq_release,
2113         .poll           = swaps_poll,
2114 };
2115
2116 static int __init procswaps_init(void)
2117 {
2118         proc_create("swaps", 0, NULL, &proc_swaps_operations);
2119         return 0;
2120 }
2121 __initcall(procswaps_init);
2122 #endif /* CONFIG_PROC_FS */
2123
2124 #ifdef MAX_SWAPFILES_CHECK
2125 static int __init max_swapfiles_check(void)
2126 {
2127         MAX_SWAPFILES_CHECK();
2128         return 0;
2129 }
2130 late_initcall(max_swapfiles_check);
2131 #endif
2132
2133 static struct swap_info_struct *alloc_swap_info(void)
2134 {
2135         struct swap_info_struct *p;
2136         unsigned int type;
2137
2138         p = kzalloc(sizeof(*p), GFP_KERNEL);
2139         if (!p)
2140                 return ERR_PTR(-ENOMEM);
2141
2142         spin_lock(&swap_lock);
2143         for (type = 0; type < nr_swapfiles; type++) {
2144                 if (!(swap_info[type]->flags & SWP_USED))
2145                         break;
2146         }
2147         if (type >= MAX_SWAPFILES) {
2148                 spin_unlock(&swap_lock);
2149                 kfree(p);
2150                 return ERR_PTR(-EPERM);
2151         }
2152         if (type >= nr_swapfiles) {
2153                 p->type = type;
2154                 swap_info[type] = p;
2155                 /*
2156                  * Write swap_info[type] before nr_swapfiles, in case a
2157                  * racing procfs swap_start() or swap_next() is reading them.
2158                  * (We never shrink nr_swapfiles, we never free this entry.)
2159                  */
2160                 smp_wmb();
2161                 nr_swapfiles++;
2162         } else {
2163                 kfree(p);
2164                 p = swap_info[type];
2165                 /*
2166                  * Do not memset this entry: a racing procfs swap_next()
2167                  * would be relying on p->type to remain valid.
2168                  */
2169         }
2170         INIT_LIST_HEAD(&p->first_swap_extent.list);
2171         plist_node_init(&p->list, 0);
2172         plist_node_init(&p->avail_list, 0);
2173         p->flags = SWP_USED;
2174         spin_unlock(&swap_lock);
2175         spin_lock_init(&p->lock);
2176
2177         return p;
2178 }
2179
2180 static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
2181 {
2182         int error;
2183
2184         if (S_ISBLK(inode->i_mode)) {
2185                 p->bdev = bdgrab(I_BDEV(inode));
2186                 error = blkdev_get(p->bdev,
2187                                    FMODE_READ | FMODE_WRITE | FMODE_EXCL, p);
2188                 if (error < 0) {
2189                         p->bdev = NULL;
2190                         return error;
2191                 }
2192                 p->old_block_size = block_size(p->bdev);
2193                 error = set_blocksize(p->bdev, PAGE_SIZE);
2194                 if (error < 0)
2195                         return error;
2196                 p->flags |= SWP_BLKDEV;
2197         } else if (S_ISREG(inode->i_mode)) {
2198                 p->bdev = inode->i_sb->s_bdev;
2199                 inode_lock(inode);
2200                 if (IS_SWAPFILE(inode))
2201                         return -EBUSY;
2202         } else
2203                 return -EINVAL;
2204
2205         return 0;
2206 }
2207
2208 static unsigned long read_swap_header(struct swap_info_struct *p,
2209                                         union swap_header *swap_header,
2210                                         struct inode *inode)
2211 {
2212         int i;
2213         unsigned long maxpages;
2214         unsigned long swapfilepages;
2215         unsigned long last_page;
2216
2217         if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
2218                 pr_err("Unable to find swap-space signature\n");
2219                 return 0;
2220         }
2221
2222         /* swap partition endianess hack... */
2223         if (swab32(swap_header->info.version) == 1) {
2224                 swab32s(&swap_header->info.version);
2225                 swab32s(&swap_header->info.last_page);
2226                 swab32s(&swap_header->info.nr_badpages);
2227                 for (i = 0; i < swap_header->info.nr_badpages; i++)
2228                         swab32s(&swap_header->info.badpages[i]);
2229         }
2230         /* Check the swap header's sub-version */
2231         if (swap_header->info.version != 1) {
2232                 pr_warn("Unable to handle swap header version %d\n",
2233                         swap_header->info.version);
2234                 return 0;
2235         }
2236
2237         p->lowest_bit  = 1;
2238         p->cluster_next = 1;
2239         p->cluster_nr = 0;
2240
2241         /*
2242          * Find out how many pages are allowed for a single swap
2243          * device. There are two limiting factors: 1) the number
2244          * of bits for the swap offset in the swp_entry_t type, and
2245          * 2) the number of bits in the swap pte as defined by the
2246          * different architectures. In order to find the
2247          * largest possible bit mask, a swap entry with swap type 0
2248          * and swap offset ~0UL is created, encoded to a swap pte,
2249          * decoded to a swp_entry_t again, and finally the swap
2250          * offset is extracted. This will mask all the bits from
2251          * the initial ~0UL mask that can't be encoded in either
2252          * the swp_entry_t or the architecture definition of a
2253          * swap pte.
2254          */
2255         maxpages = swp_offset(pte_to_swp_entry(
2256                         swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
2257         last_page = swap_header->info.last_page;
2258         if (last_page > maxpages) {
2259                 pr_warn("Truncating oversized swap area, only using %luk out of %luk\n",
2260                         maxpages << (PAGE_SHIFT - 10),
2261                         last_page << (PAGE_SHIFT - 10));
2262         }
2263         if (maxpages > last_page) {
2264                 maxpages = last_page + 1;
2265                 /* p->max is an unsigned int: don't overflow it */
2266                 if ((unsigned int)maxpages == 0)
2267                         maxpages = UINT_MAX;
2268         }
2269         p->highest_bit = maxpages - 1;
2270
2271         if (!maxpages)
2272                 return 0;
2273         swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
2274         if (swapfilepages && maxpages > swapfilepages) {
2275                 pr_warn("Swap area shorter than signature indicates\n");
2276                 return 0;
2277         }
2278         if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
2279                 return 0;
2280         if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
2281                 return 0;
2282
2283         return maxpages;
2284 }
2285
2286 static int setup_swap_map_and_extents(struct swap_info_struct *p,
2287                                         union swap_header *swap_header,
2288                                         unsigned char *swap_map,
2289                                         struct swap_cluster_info *cluster_info,
2290                                         unsigned long maxpages,
2291                                         sector_t *span)
2292 {
2293         int i;
2294         unsigned int nr_good_pages;
2295         int nr_extents;
2296         unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
2297         unsigned long idx = p->cluster_next / SWAPFILE_CLUSTER;
2298
2299         nr_good_pages = maxpages - 1;   /* omit header page */
2300
2301         cluster_list_init(&p->free_clusters);
2302         cluster_list_init(&p->discard_clusters);
2303
2304         for (i = 0; i < swap_header->info.nr_badpages; i++) {
2305                 unsigned int page_nr = swap_header->info.badpages[i];
2306                 if (page_nr == 0 || page_nr > swap_header->info.last_page)
2307                         return -EINVAL;
2308                 if (page_nr < maxpages) {
2309                         swap_map[page_nr] = SWAP_MAP_BAD;
2310                         nr_good_pages--;
2311                         /*
2312                          * Haven't marked the cluster free yet, no list
2313                          * operation involved
2314                          */
2315                         inc_cluster_info_page(p, cluster_info, page_nr);
2316                 }
2317         }
2318
2319         /* Haven't marked the cluster free yet, no list operation involved */
2320         for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++)
2321                 inc_cluster_info_page(p, cluster_info, i);
2322
2323         if (nr_good_pages) {
2324                 swap_map[0] = SWAP_MAP_BAD;
2325                 /*
2326                  * Not mark the cluster free yet, no list
2327                  * operation involved
2328                  */
2329                 inc_cluster_info_page(p, cluster_info, 0);
2330                 p->max = maxpages;
2331                 p->pages = nr_good_pages;
2332                 nr_extents = setup_swap_extents(p, span);
2333                 if (nr_extents < 0)
2334                         return nr_extents;
2335                 nr_good_pages = p->pages;
2336         }
2337         if (!nr_good_pages) {
2338                 pr_warn("Empty swap-file\n");
2339                 return -EINVAL;
2340         }
2341
2342         if (!cluster_info)
2343                 return nr_extents;
2344
2345         for (i = 0; i < nr_clusters; i++) {
2346                 if (!cluster_count(&cluster_info[idx])) {
2347                         cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
2348                         cluster_list_add_tail(&p->free_clusters, cluster_info,
2349                                               idx);
2350                 }
2351                 idx++;
2352                 if (idx == nr_clusters)
2353                         idx = 0;
2354         }
2355         return nr_extents;
2356 }
2357
2358 /*
2359  * Helper to sys_swapon determining if a given swap
2360  * backing device queue supports DISCARD operations.
2361  */
2362 static bool swap_discardable(struct swap_info_struct *si)
2363 {
2364         struct request_queue *q = bdev_get_queue(si->bdev);
2365
2366         if (!q || !blk_queue_discard(q))
2367                 return false;
2368
2369         return true;
2370 }
2371
2372 SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
2373 {
2374         struct swap_info_struct *p;
2375         struct filename *name;
2376         struct file *swap_file = NULL;
2377         struct address_space *mapping;
2378         int prio;
2379         int error;
2380         union swap_header *swap_header;
2381         int nr_extents;
2382         sector_t span;
2383         unsigned long maxpages;
2384         unsigned char *swap_map = NULL;
2385         struct swap_cluster_info *cluster_info = NULL;
2386         unsigned long *frontswap_map = NULL;
2387         struct page *page = NULL;
2388         struct inode *inode = NULL;
2389
2390         if (swap_flags & ~SWAP_FLAGS_VALID)
2391                 return -EINVAL;
2392
2393         if (!capable(CAP_SYS_ADMIN))
2394                 return -EPERM;
2395
2396         p = alloc_swap_info();
2397         if (IS_ERR(p))
2398                 return PTR_ERR(p);
2399
2400         INIT_WORK(&p->discard_work, swap_discard_work);
2401
2402         name = getname(specialfile);
2403         if (IS_ERR(name)) {
2404                 error = PTR_ERR(name);
2405                 name = NULL;
2406                 goto bad_swap;
2407         }
2408         swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
2409         if (IS_ERR(swap_file)) {
2410                 error = PTR_ERR(swap_file);
2411                 swap_file = NULL;
2412                 goto bad_swap;
2413         }
2414
2415         p->swap_file = swap_file;
2416         mapping = swap_file->f_mapping;
2417         inode = mapping->host;
2418
2419         /* If S_ISREG(inode->i_mode) will do inode_lock(inode); */
2420         error = claim_swapfile(p, inode);
2421         if (unlikely(error))
2422                 goto bad_swap;
2423
2424         /*
2425          * Read the swap header.
2426          */
2427         if (!mapping->a_ops->readpage) {
2428                 error = -EINVAL;
2429                 goto bad_swap;
2430         }
2431         page = read_mapping_page(mapping, 0, swap_file);
2432         if (IS_ERR(page)) {
2433                 error = PTR_ERR(page);
2434                 goto bad_swap;
2435         }
2436         swap_header = kmap(page);
2437
2438         maxpages = read_swap_header(p, swap_header, inode);
2439         if (unlikely(!maxpages)) {
2440                 error = -EINVAL;
2441                 goto bad_swap;
2442         }
2443
2444         /* OK, set up the swap map and apply the bad block list */
2445         swap_map = vzalloc(maxpages);
2446         if (!swap_map) {
2447                 error = -ENOMEM;
2448                 goto bad_swap;
2449         }
2450         if (p->bdev && blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2451                 int cpu;
2452
2453                 p->flags |= SWP_SOLIDSTATE;
2454                 /*
2455                  * select a random position to start with to help wear leveling
2456                  * SSD
2457                  */
2458                 p->cluster_next = 1 + (prandom_u32() % p->highest_bit);
2459
2460                 cluster_info = vzalloc(DIV_ROUND_UP(maxpages,
2461                         SWAPFILE_CLUSTER) * sizeof(*cluster_info));
2462                 if (!cluster_info) {
2463                         error = -ENOMEM;
2464                         goto bad_swap;
2465                 }
2466                 p->percpu_cluster = alloc_percpu(struct percpu_cluster);
2467                 if (!p->percpu_cluster) {
2468                         error = -ENOMEM;
2469                         goto bad_swap;
2470                 }
2471                 for_each_possible_cpu(cpu) {
2472                         struct percpu_cluster *cluster;
2473                         cluster = per_cpu_ptr(p->percpu_cluster, cpu);
2474                         cluster_set_null(&cluster->index);
2475                 }
2476         }
2477
2478         error = swap_cgroup_swapon(p->type, maxpages);
2479         if (error)
2480                 goto bad_swap;
2481
2482         nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
2483                 cluster_info, maxpages, &span);
2484         if (unlikely(nr_extents < 0)) {
2485                 error = nr_extents;
2486                 goto bad_swap;
2487         }
2488         /* frontswap enabled? set up bit-per-page map for frontswap */
2489         if (IS_ENABLED(CONFIG_FRONTSWAP))
2490                 frontswap_map = vzalloc(BITS_TO_LONGS(maxpages) * sizeof(long));
2491
2492         if (p->bdev &&(swap_flags & SWAP_FLAG_DISCARD) && swap_discardable(p)) {
2493                 /*
2494                  * When discard is enabled for swap with no particular
2495                  * policy flagged, we set all swap discard flags here in
2496                  * order to sustain backward compatibility with older
2497                  * swapon(8) releases.
2498                  */
2499                 p->flags |= (SWP_DISCARDABLE | SWP_AREA_DISCARD |
2500                              SWP_PAGE_DISCARD);
2501
2502                 /*
2503                  * By flagging sys_swapon, a sysadmin can tell us to
2504                  * either do single-time area discards only, or to just
2505                  * perform discards for released swap page-clusters.
2506                  * Now it's time to adjust the p->flags accordingly.
2507                  */
2508                 if (swap_flags & SWAP_FLAG_DISCARD_ONCE)
2509                         p->flags &= ~SWP_PAGE_DISCARD;
2510                 else if (swap_flags & SWAP_FLAG_DISCARD_PAGES)
2511                         p->flags &= ~SWP_AREA_DISCARD;
2512
2513                 /* issue a swapon-time discard if it's still required */
2514                 if (p->flags & SWP_AREA_DISCARD) {
2515                         int err = discard_swap(p);
2516                         if (unlikely(err))
2517                                 pr_err("swapon: discard_swap(%p): %d\n",
2518                                         p, err);
2519                 }
2520         }
2521
2522         mutex_lock(&swapon_mutex);
2523         prio = -1;
2524         if (swap_flags & SWAP_FLAG_PREFER)
2525                 prio =
2526                   (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2527         enable_swap_info(p, prio, swap_map, cluster_info, frontswap_map);
2528
2529         pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s%s\n",
2530                 p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
2531                 nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2532                 (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2533                 (p->flags & SWP_DISCARDABLE) ? "D" : "",
2534                 (p->flags & SWP_AREA_DISCARD) ? "s" : "",
2535                 (p->flags & SWP_PAGE_DISCARD) ? "c" : "",
2536                 (frontswap_map) ? "FS" : "");
2537
2538         mutex_unlock(&swapon_mutex);
2539         atomic_inc(&proc_poll_event);
2540         wake_up_interruptible(&proc_poll_wait);
2541
2542         if (S_ISREG(inode->i_mode))
2543                 inode->i_flags |= S_SWAPFILE;
2544         error = 0;
2545         goto out;
2546 bad_swap:
2547         free_percpu(p->percpu_cluster);
2548         p->percpu_cluster = NULL;
2549         if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
2550                 set_blocksize(p->bdev, p->old_block_size);
2551                 blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
2552         }
2553         destroy_swap_extents(p);
2554         swap_cgroup_swapoff(p->type);
2555         spin_lock(&swap_lock);
2556         p->swap_file = NULL;
2557         p->flags = 0;
2558         spin_unlock(&swap_lock);
2559         vfree(swap_map);
2560         vfree(cluster_info);
2561         if (swap_file) {
2562                 if (inode && S_ISREG(inode->i_mode)) {
2563                         inode_unlock(inode);
2564                         inode = NULL;
2565                 }
2566                 filp_close(swap_file, NULL);
2567         }
2568 out:
2569         if (page && !IS_ERR(page)) {
2570                 kunmap(page);
2571                 put_page(page);
2572         }
2573         if (name)
2574                 putname(name);
2575         if (inode && S_ISREG(inode->i_mode))
2576                 inode_unlock(inode);
2577         return error;
2578 }
2579
2580 void si_swapinfo(struct sysinfo *val)
2581 {
2582         unsigned int type;
2583         unsigned long nr_to_be_unused = 0;
2584
2585         spin_lock(&swap_lock);
2586         for (type = 0; type < nr_swapfiles; type++) {
2587                 struct swap_info_struct *si = swap_info[type];
2588
2589                 if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2590                         nr_to_be_unused += si->inuse_pages;
2591         }
2592         val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
2593         val->totalswap = total_swap_pages + nr_to_be_unused;
2594         spin_unlock(&swap_lock);
2595 }
2596
2597 /*
2598  * Verify that a swap entry is valid and increment its swap map count.
2599  *
2600  * Returns error code in following case.
2601  * - success -> 0
2602  * - swp_entry is invalid -> EINVAL
2603  * - swp_entry is migration entry -> EINVAL
2604  * - swap-cache reference is requested but there is already one. -> EEXIST
2605  * - swap-cache reference is requested but the entry is not used. -> ENOENT
2606  * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2607  */
2608 static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2609 {
2610         struct swap_info_struct *p;
2611         unsigned long offset, type;
2612         unsigned char count;
2613         unsigned char has_cache;
2614         int err = -EINVAL;
2615
2616         if (non_swap_entry(entry))
2617                 goto out;
2618
2619         type = swp_type(entry);
2620         if (type >= nr_swapfiles)
2621                 goto bad_file;
2622         p = swap_info[type];
2623         offset = swp_offset(entry);
2624
2625         spin_lock(&p->lock);
2626         if (unlikely(offset >= p->max))
2627                 goto unlock_out;
2628
2629         count = p->swap_map[offset];
2630
2631         /*
2632          * swapin_readahead() doesn't check if a swap entry is valid, so the
2633          * swap entry could be SWAP_MAP_BAD. Check here with lock held.
2634          */
2635         if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
2636                 err = -ENOENT;
2637                 goto unlock_out;
2638         }
2639
2640         has_cache = count & SWAP_HAS_CACHE;
2641         count &= ~SWAP_HAS_CACHE;
2642         err = 0;
2643
2644         if (usage == SWAP_HAS_CACHE) {
2645
2646                 /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2647                 if (!has_cache && count)
2648                         has_cache = SWAP_HAS_CACHE;
2649                 else if (has_cache)             /* someone else added cache */
2650                         err = -EEXIST;
2651                 else                            /* no users remaining */
2652                         err = -ENOENT;
2653
2654         } else if (count || has_cache) {
2655
2656                 if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2657                         count += usage;
2658                 else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2659                         err = -EINVAL;
2660                 else if (swap_count_continued(p, offset, count))
2661                         count = COUNT_CONTINUED;
2662                 else
2663                         err = -ENOMEM;
2664         } else
2665                 err = -ENOENT;                  /* unused swap entry */
2666
2667         p->swap_map[offset] = count | has_cache;
2668
2669 unlock_out:
2670         spin_unlock(&p->lock);
2671 out:
2672         return err;
2673
2674 bad_file:
2675         pr_err("swap_dup: %s%08lx\n", Bad_file, entry.val);
2676         goto out;
2677 }
2678
2679 /*
2680  * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2681  * (in which case its reference count is never incremented).
2682  */
2683 void swap_shmem_alloc(swp_entry_t entry)
2684 {
2685         __swap_duplicate(entry, SWAP_MAP_SHMEM);
2686 }
2687
2688 /*
2689  * Increase reference count of swap entry by 1.
2690  * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2691  * but could not be atomically allocated.  Returns 0, just as if it succeeded,
2692  * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2693  * might occur if a page table entry has got corrupted.
2694  */
2695 int swap_duplicate(swp_entry_t entry)
2696 {
2697         int err = 0;
2698
2699         while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2700                 err = add_swap_count_continuation(entry, GFP_ATOMIC);
2701         return err;
2702 }
2703
2704 /*
2705  * @entry: swap entry for which we allocate swap cache.
2706  *
2707  * Called when allocating swap cache for existing swap entry,
2708  * This can return error codes. Returns 0 at success.
2709  * -EBUSY means there is a swap cache.
2710  * Note: return code is different from swap_duplicate().
2711  */
2712 int swapcache_prepare(swp_entry_t entry)
2713 {
2714         return __swap_duplicate(entry, SWAP_HAS_CACHE);
2715 }
2716
2717 struct swap_info_struct *page_swap_info(struct page *page)
2718 {
2719         swp_entry_t swap = { .val = page_private(page) };
2720         return swap_info[swp_type(swap)];
2721 }
2722
2723 /*
2724  * out-of-line __page_file_ methods to avoid include hell.
2725  */
2726 struct address_space *__page_file_mapping(struct page *page)
2727 {
2728         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
2729         return page_swap_info(page)->swap_file->f_mapping;
2730 }
2731 EXPORT_SYMBOL_GPL(__page_file_mapping);
2732
2733 pgoff_t __page_file_index(struct page *page)
2734 {
2735         swp_entry_t swap = { .val = page_private(page) };
2736         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
2737         return swp_offset(swap);
2738 }
2739 EXPORT_SYMBOL_GPL(__page_file_index);
2740
2741 /*
2742  * add_swap_count_continuation - called when a swap count is duplicated
2743  * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2744  * page of the original vmalloc'ed swap_map, to hold the continuation count
2745  * (for that entry and for its neighbouring PAGE_SIZE swap entries).  Called
2746  * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2747  *
2748  * These continuation pages are seldom referenced: the common paths all work
2749  * on the original swap_map, only referring to a continuation page when the
2750  * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2751  *
2752  * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2753  * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2754  * can be called after dropping locks.
2755  */
2756 int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2757 {
2758         struct swap_info_struct *si;
2759         struct page *head;
2760         struct page *page;
2761         struct page *list_page;
2762         pgoff_t offset;
2763         unsigned char count;
2764
2765         /*
2766          * When debugging, it's easier to use __GFP_ZERO here; but it's better
2767          * for latency not to zero a page while GFP_ATOMIC and holding locks.
2768          */
2769         page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2770
2771         si = swap_info_get(entry);
2772         if (!si) {
2773                 /*
2774                  * An acceptable race has occurred since the failing
2775                  * __swap_duplicate(): the swap entry has been freed,
2776                  * perhaps even the whole swap_map cleared for swapoff.
2777                  */
2778                 goto outer;
2779         }
2780
2781         offset = swp_offset(entry);
2782         count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2783
2784         if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2785                 /*
2786                  * The higher the swap count, the more likely it is that tasks
2787                  * will race to add swap count continuation: we need to avoid
2788                  * over-provisioning.
2789                  */
2790                 goto out;
2791         }
2792
2793         if (!page) {
2794                 spin_unlock(&si->lock);
2795                 return -ENOMEM;
2796         }
2797
2798         /*
2799          * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2800          * no architecture is using highmem pages for kernel page tables: so it
2801          * will not corrupt the GFP_ATOMIC caller's atomic page table kmaps.
2802          */
2803         head = vmalloc_to_page(si->swap_map + offset);
2804         offset &= ~PAGE_MASK;
2805
2806         /*
2807          * Page allocation does not initialize the page's lru field,
2808          * but it does always reset its private field.
2809          */
2810         if (!page_private(head)) {
2811                 BUG_ON(count & COUNT_CONTINUED);
2812                 INIT_LIST_HEAD(&head->lru);
2813                 set_page_private(head, SWP_CONTINUED);
2814                 si->flags |= SWP_CONTINUED;
2815         }
2816
2817         list_for_each_entry(list_page, &head->lru, lru) {
2818                 unsigned char *map;
2819
2820                 /*
2821                  * If the previous map said no continuation, but we've found
2822                  * a continuation page, free our allocation and use this one.
2823                  */
2824                 if (!(count & COUNT_CONTINUED))
2825                         goto out;
2826
2827                 map = kmap_atomic(list_page) + offset;
2828                 count = *map;
2829                 kunmap_atomic(map);
2830
2831                 /*
2832                  * If this continuation count now has some space in it,
2833                  * free our allocation and use this one.
2834                  */
2835                 if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2836                         goto out;
2837         }
2838
2839         list_add_tail(&page->lru, &head->lru);
2840         page = NULL;                    /* now it's attached, don't free it */
2841 out:
2842         spin_unlock(&si->lock);
2843 outer:
2844         if (page)
2845                 __free_page(page);
2846         return 0;
2847 }
2848
2849 /*
2850  * swap_count_continued - when the original swap_map count is incremented
2851  * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2852  * into, carry if so, or else fail until a new continuation page is allocated;
2853  * when the original swap_map count is decremented from 0 with continuation,
2854  * borrow from the continuation and report whether it still holds more.
2855  * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2856  */
2857 static bool swap_count_continued(struct swap_info_struct *si,
2858                                  pgoff_t offset, unsigned char count)
2859 {
2860         struct page *head;
2861         struct page *page;
2862         unsigned char *map;
2863
2864         head = vmalloc_to_page(si->swap_map + offset);
2865         if (page_private(head) != SWP_CONTINUED) {
2866                 BUG_ON(count & COUNT_CONTINUED);
2867                 return false;           /* need to add count continuation */
2868         }
2869
2870         offset &= ~PAGE_MASK;
2871         page = list_entry(head->lru.next, struct page, lru);
2872         map = kmap_atomic(page) + offset;
2873
2874         if (count == SWAP_MAP_MAX)      /* initial increment from swap_map */
2875                 goto init_map;          /* jump over SWAP_CONT_MAX checks */
2876
2877         if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2878                 /*
2879                  * Think of how you add 1 to 999
2880                  */
2881                 while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2882                         kunmap_atomic(map);
2883                         page = list_entry(page->lru.next, struct page, lru);
2884                         BUG_ON(page == head);
2885                         map = kmap_atomic(page) + offset;
2886                 }
2887                 if (*map == SWAP_CONT_MAX) {
2888                         kunmap_atomic(map);
2889                         page = list_entry(page->lru.next, struct page, lru);
2890                         if (page == head)
2891                                 return false;   /* add count continuation */
2892                         map = kmap_atomic(page) + offset;
2893 init_map:               *map = 0;               /* we didn't zero the page */
2894                 }
2895                 *map += 1;
2896                 kunmap_atomic(map);
2897                 page = list_entry(page->lru.prev, struct page, lru);
2898                 while (page != head) {
2899                         map = kmap_atomic(page) + offset;
2900                         *map = COUNT_CONTINUED;
2901                         kunmap_atomic(map);
2902                         page = list_entry(page->lru.prev, struct page, lru);
2903                 }
2904                 return true;                    /* incremented */
2905
2906         } else {                                /* decrementing */
2907                 /*
2908                  * Think of how you subtract 1 from 1000
2909                  */
2910                 BUG_ON(count != COUNT_CONTINUED);
2911                 while (*map == COUNT_CONTINUED) {
2912                         kunmap_atomic(map);
2913                         page = list_entry(page->lru.next, struct page, lru);
2914                         BUG_ON(page == head);
2915                         map = kmap_atomic(page) + offset;
2916                 }
2917                 BUG_ON(*map == 0);
2918                 *map -= 1;
2919                 if (*map == 0)
2920                         count = 0;
2921                 kunmap_atomic(map);
2922                 page = list_entry(page->lru.prev, struct page, lru);
2923                 while (page != head) {
2924                         map = kmap_atomic(page) + offset;
2925                         *map = SWAP_CONT_MAX | count;
2926                         count = COUNT_CONTINUED;
2927                         kunmap_atomic(map);
2928                         page = list_entry(page->lru.prev, struct page, lru);
2929                 }
2930                 return count == COUNT_CONTINUED;
2931         }
2932 }
2933
2934 /*
2935  * free_swap_count_continuations - swapoff free all the continuation pages
2936  * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2937  */
2938 static void free_swap_count_continuations(struct swap_info_struct *si)
2939 {
2940         pgoff_t offset;
2941
2942         for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2943                 struct page *head;
2944                 head = vmalloc_to_page(si->swap_map + offset);
2945                 if (page_private(head)) {
2946                         struct page *page, *next;
2947
2948                         list_for_each_entry_safe(page, next, &head->lru, lru) {
2949                                 list_del(&page->lru);
2950                                 __free_page(page);
2951                         }
2952                 }
2953         }
2954 }