kernel/fork.c

   1 /*
   2  *  linux/kernel/fork.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  */
   6
   7 /*
   8  *  'fork.c' contains the help-routines for the 'fork' system call
   9  * (see also entry.S and others).
  10  * Fork is rather simple, once you get the hang of it, but the memory
  11  * management can be a bitch. See 'mm/memory.c': 'copy_page_range()'
  12  */
  13
  14 #include <linux/slab.h>
  15 #include <linux/init.h>
  16 #include <linux/unistd.h>
  17 #include <linux/module.h>
  18 #include <linux/vmalloc.h>
  19 #include <linux/completion.h>
  20 #include <linux/personality.h>
  21 #include <linux/mempolicy.h>
  22 #include <linux/sem.h>
  23 #include <linux/file.h>
  24 #include <linux/fdtable.h>
  25 #include <linux/iocontext.h>
  26 #include <linux/key.h>
  27 #include <linux/binfmts.h>
  28 #include <linux/mman.h>
  29 #include <linux/mmu_notifier.h>
  30 #include <linux/fs.h>
  31 #include <linux/mm.h>
  32 #include <linux/vmacache.h>
  33 #include <linux/nsproxy.h>
  34 #include <linux/capability.h>
  35 #include <linux/cpu.h>
  36 #include <linux/cgroup.h>
  37 #include <linux/security.h>
  38 #include <linux/hugetlb.h>
  39 #include <linux/seccomp.h>
  40 #include <linux/swap.h>
  41 #include <linux/syscalls.h>
  42 #include <linux/jiffies.h>
  43 #include <linux/futex.h>
  44 #include <linux/compat.h>
  45 #include <linux/kthread.h>
  46 #include <linux/task_io_accounting_ops.h>
  47 #include <linux/rcupdate.h>
  48 #include <linux/ptrace.h>
  49 #include <linux/mount.h>
  50 #include <linux/audit.h>
  51 #include <linux/memcontrol.h>
  52 #include <linux/ftrace.h>
  53 #include <linux/proc_fs.h>
  54 #include <linux/profile.h>
  55 #include <linux/rmap.h>
  56 #include <linux/ksm.h>
  57 #include <linux/acct.h>
  58 #include <linux/tsacct_kern.h>
  59 #include <linux/cn_proc.h>
  60 #include <linux/freezer.h>
  61 #include <linux/delayacct.h>
  62 #include <linux/taskstats_kern.h>
  63 #include <linux/random.h>
  64 #include <linux/tty.h>
  65 #include <linux/blkdev.h>
  66 #include <linux/fs_struct.h>
  67 #include <linux/magic.h>
  68 #include <linux/perf_event.h>
  69 #include <linux/posix-timers.h>
  70 #include <linux/user-return-notifier.h>
  71 #include <linux/oom.h>
  72 #include <linux/khugepaged.h>
  73 #include <linux/signalfd.h>
  74 #include <linux/uprobes.h>
  75 #include <linux/aio.h>
  76 #include <linux/compiler.h>
  77
  78 #include <asm/pgtable.h>
  79 #include <asm/pgalloc.h>
  80 #include <asm/uaccess.h>
  81 #include <asm/mmu_context.h>
  82 #include <asm/cacheflush.h>
  83 #include <asm/tlbflush.h>
  84
  85 #include <trace/events/sched.h>
  86
  87 #define CREATE_TRACE_POINTS
  88 #include <trace/events/task.h>
  89
  90 /*
  91  * Protected counters by write_lock_irq(&tasklist_lock)
  92  */
  93 unsigned long total_forks;      /* Handle normal Linux uptimes. */
  94 int nr_threads;                 /* The idle threads do not count.. */
  95
  96 int max_threads;                /* tunable limit on nr_threads */
  97
  98 DEFINE_PER_CPU(unsigned long, process_counts) = 0;
  99
 100 __cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
 101
 102 #ifdef CONFIG_PROVE_RCU
 103 int lockdep_tasklist_lock_is_held(void)
 104 {
 105         return lockdep_is_held(&tasklist_lock);
 106 }
 107 EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
 108 #endif /* #ifdef CONFIG_PROVE_RCU */
 109
 110 int nr_processes(void)
 111 {
 112         int cpu;
 113         int total = 0;
 114
 115         for_each_possible_cpu(cpu)
 116                 total += per_cpu(process_counts, cpu);
 117
 118         return total;
 119 }
 120
 121 void __weak arch_release_task_struct(struct task_struct *tsk)
 122 {
 123 }
 124
 125 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
 126 static struct kmem_cache *task_struct_cachep;
 127
 128 static inline struct task_struct *alloc_task_struct_node(int node)
 129 {
 130         return kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL, node);
 131 }
 132
 133 static inline void free_task_struct(struct task_struct *tsk)
 134 {
 135         kmem_cache_free(task_struct_cachep, tsk);
 136 }
 137 #endif
 138
 139 void __weak arch_release_thread_info(struct thread_info *ti)
 140 {
 141 }
 142
 143 #ifndef CONFIG_ARCH_THREAD_INFO_ALLOCATOR
 144
 145 /*
 146  * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
 147  * kmemcache based allocator.
 148  */
 149 # if THREAD_SIZE >= PAGE_SIZE
 150 static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
 151                                                   int node)
 152 {
 153         struct page *page = alloc_kmem_pages_node(node, THREADINFO_GFP,
 154                                                   THREAD_SIZE_ORDER);
 155
 156         return page ? page_address(page) : NULL;
 157 }
 158
 159 static inline void free_thread_info(struct thread_info *ti)
 160 {
 161         free_kmem_pages((unsigned long)ti, THREAD_SIZE_ORDER);
 162 }
 163 # else
 164 static struct kmem_cache *thread_info_cache;
 165
 166 static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
 167                                                   int node)
 168 {
 169         return kmem_cache_alloc_node(thread_info_cache, THREADINFO_GFP, node);
 170 }
 171
 172 static void free_thread_info(struct thread_info *ti)
 173 {
 174         kmem_cache_free(thread_info_cache, ti);
 175 }
 176
 177 void thread_info_cache_init(void)
 178 {
 179         thread_info_cache = kmem_cache_create("thread_info", THREAD_SIZE,
 180                                               THREAD_SIZE, 0, NULL);
 181         BUG_ON(thread_info_cache == NULL);
 182 }
 183 # endif
 184 #endif
 185
 186 /* SLAB cache for signal_struct structures (tsk->signal) */
 187 static struct kmem_cache *signal_cachep;
 188
 189 /* SLAB cache for sighand_struct structures (tsk->sighand) */
 190 struct kmem_cache *sighand_cachep;
 191
 192 /* SLAB cache for files_struct structures (tsk->files) */
 193 struct kmem_cache *files_cachep;
 194
 195 /* SLAB cache for fs_struct structures (tsk->fs) */
 196 struct kmem_cache *fs_cachep;
 197
 198 /* SLAB cache for vm_area_struct structures */
 199 struct kmem_cache *vm_area_cachep;
 200
 201 /* SLAB cache for mm_struct structures (tsk->mm) */
 202 static struct kmem_cache *mm_cachep;
 203
 204 static void account_kernel_stack(struct thread_info *ti, int account)
 205 {
 206         struct zone *zone = page_zone(virt_to_page(ti));
 207
 208         mod_zone_page_state(zone, NR_KERNEL_STACK, account);
 209 }
 210
 211 void free_task(struct task_struct *tsk)
 212 {
 213         account_kernel_stack(tsk->stack, -1);
 214         arch_release_thread_info(tsk->stack);
 215         free_thread_info(tsk->stack);
 216         rt_mutex_debug_task_free(tsk);
 217         ftrace_graph_exit_task(tsk);
 218         put_seccomp_filter(tsk);
 219         arch_release_task_struct(tsk);
 220         free_task_struct(tsk);
 221 }
 222 EXPORT_SYMBOL(free_task);
 223
 224 static inline void free_signal_struct(struct signal_struct *sig)
 225 {
 226         taskstats_tgid_free(sig);
 227         sched_autogroup_exit(sig);
 228         kmem_cache_free(signal_cachep, sig);
 229 }
 230
 231 static inline void put_signal_struct(struct signal_struct *sig)
 232 {
 233         if (atomic_dec_and_test(&sig->sigcnt))
 234                 free_signal_struct(sig);
 235 }
 236
 237 void __put_task_struct(struct task_struct *tsk)
 238 {
 239         WARN_ON(!tsk->exit_state);
 240         WARN_ON(atomic_read(&tsk->usage));
 241         WARN_ON(tsk == current);
 242
 243         task_numa_free(tsk);
 244         security_task_free(tsk);
 245         exit_creds(tsk);
 246         delayacct_tsk_free(tsk);
 247         put_signal_struct(tsk->signal);
 248
 249         if (!profile_handoff_task(tsk))
 250                 free_task(tsk);
 251 }
 252 EXPORT_SYMBOL_GPL(__put_task_struct);
 253
 254 void __init __weak arch_task_cache_init(void) { }
 255
 256 void __init fork_init(unsigned long mempages)
 257 {
 258 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
 259 #ifndef ARCH_MIN_TASKALIGN
 260 #define ARCH_MIN_TASKALIGN      L1_CACHE_BYTES
 261 #endif
 262         /* create a slab on which task_structs can be allocated */
 263         task_struct_cachep =
 264                 kmem_cache_create("task_struct", sizeof(struct task_struct),
 265                         ARCH_MIN_TASKALIGN, SLAB_PANIC | SLAB_NOTRACK, NULL);
 266 #endif
 267
 268         /* do the arch specific task caches init */
 269         arch_task_cache_init();
 270
 271         /*
 272          * The default maximum number of threads is set to a safe
 273          * value: the thread structures can take up at most half
 274          * of memory.
 275          */
 276         max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
 277
 278         /*
 279          * we need to allow at least 20 threads to boot a system
 280          */
 281         if (max_threads < 20)
 282                 max_threads = 20;
 283
 284         init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
 285         init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
 286         init_task.signal->rlim[RLIMIT_SIGPENDING] =
 287                 init_task.signal->rlim[RLIMIT_NPROC];
 288 }
 289
 290 int __weak arch_dup_task_struct(struct task_struct *dst,
 291                                                struct task_struct *src)
 292 {
 293         *dst = *src;
 294         return 0;
 295 }
 296
 297 void set_task_stack_end_magic(struct task_struct *tsk)
 298 {
 299         unsigned long *stackend;
 300
 301         stackend = end_of_stack(tsk);
 302         *stackend = STACK_END_MAGIC;    /* for overflow detection */
 303 }
 304
 305 static struct task_struct *dup_task_struct(struct task_struct *orig)
 306 {
 307         struct task_struct *tsk;
 308         struct thread_info *ti;
 309         int node = tsk_fork_get_node(orig);
 310         int err;
 311
 312         tsk = alloc_task_struct_node(node);
 313         if (!tsk)
 314                 return NULL;
 315
 316         ti = alloc_thread_info_node(tsk, node);
 317         if (!ti)
 318                 goto free_tsk;
 319
 320         err = arch_dup_task_struct(tsk, orig);
 321         if (err)
 322                 goto free_ti;
 323
 324         tsk->stack = ti;
 325 #ifdef CONFIG_SECCOMP
 326         /*
 327          * We must handle setting up seccomp filters once we're under
 328          * the sighand lock in case orig has changed between now and
 329          * then. Until then, filter must be NULL to avoid messing up
 330          * the usage counts on the error path calling free_task.
 331          */
 332         tsk->seccomp.filter = NULL;
 333 #endif
 334
 335         setup_thread_stack(tsk, orig);
 336         clear_user_return_notifier(tsk);
 337         clear_tsk_need_resched(tsk);
 338         set_task_stack_end_magic(tsk);
 339
 340 #ifdef CONFIG_CC_STACKPROTECTOR
 341         tsk->stack_canary = get_random_int();
 342 #endif
 343
 344         /*
 345          * One for us, one for whoever does the "release_task()" (usually
 346          * parent)
 347          */
 348         atomic_set(&tsk->usage, 2);
 349 #ifdef CONFIG_BLK_DEV_IO_TRACE
 350         tsk->btrace_seq = 0;
 351 #endif
 352         tsk->splice_pipe = NULL;
 353         tsk->task_frag.page = NULL;
 354
 355         account_kernel_stack(ti, 1);
 356
 357         return tsk;
 358
 359 free_ti:
 360         free_thread_info(ti);
 361 free_tsk:
 362         free_task_struct(tsk);
 363         return NULL;
 364 }
 365
 366 #ifdef CONFIG_MMU
 367 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 368 {
 369         struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
 370         struct rb_node **rb_link, *rb_parent;
 371         int retval;
 372         unsigned long charge;
 373
 374         uprobe_start_dup_mmap();
 375         down_write(&oldmm->mmap_sem);
 376         flush_cache_dup_mm(oldmm);
 377         uprobe_dup_mmap(oldmm, mm);
 378         /*
 379          * Not linked in yet - no deadlock potential:
 380          */
 381         down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
 382
 383         mm->total_vm = oldmm->total_vm;
 384         mm->shared_vm = oldmm->shared_vm;
 385         mm->exec_vm = oldmm->exec_vm;
 386         mm->stack_vm = oldmm->stack_vm;
 387
 388         rb_link = &mm->mm_rb.rb_node;
 389         rb_parent = NULL;
 390         pprev = &mm->mmap;
 391         retval = ksm_fork(mm, oldmm);
 392         if (retval)
 393                 goto out;
 394         retval = khugepaged_fork(mm, oldmm);
 395         if (retval)
 396                 goto out;
 397
 398         prev = NULL;
 399         for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
 400                 struct file *file;
 401
 402                 if (mpnt->vm_flags & VM_DONTCOPY) {
 403                         vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
 404                                                         -vma_pages(mpnt));
 405                         continue;
 406                 }
 407                 charge = 0;
 408                 if (mpnt->vm_flags & VM_ACCOUNT) {
 409                         unsigned long len = vma_pages(mpnt);
 410
 411                         if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
 412                                 goto fail_nomem;
 413                         charge = len;
 414                 }
 415                 tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
 416                 if (!tmp)
 417                         goto fail_nomem;
 418                 *tmp = *mpnt;
 419                 INIT_LIST_HEAD(&tmp->anon_vma_chain);
 420                 retval = vma_dup_policy(mpnt, tmp);
 421                 if (retval)
 422                         goto fail_nomem_policy;
 423                 tmp->vm_mm = mm;
 424                 if (anon_vma_fork(tmp, mpnt))
 425                         goto fail_nomem_anon_vma_fork;
 426                 tmp->vm_flags &= ~VM_LOCKED;
 427                 tmp->vm_next = tmp->vm_prev = NULL;
 428                 file = tmp->vm_file;
 429                 if (file) {
 430                         struct inode *inode = file_inode(file);
 431                         struct address_space *mapping = file->f_mapping;
 432
 433                         get_file(file);
 434                         if (tmp->vm_flags & VM_DENYWRITE)
 435                                 atomic_dec(&inode->i_writecount);
 436                         mutex_lock(&mapping->i_mmap_mutex);
 437                         if (tmp->vm_flags & VM_SHARED)
 438                                 atomic_inc(&mapping->i_mmap_writable);
 439                         flush_dcache_mmap_lock(mapping);
 440                         /* insert tmp into the share list, just after mpnt */
 441                         if (unlikely(tmp->vm_flags & VM_NONLINEAR))
 442                                 vma_nonlinear_insert(tmp,
 443                                                 &mapping->i_mmap_nonlinear);
 444                         else
 445                                 vma_interval_tree_insert_after(tmp, mpnt,
 446                                                         &mapping->i_mmap);
 447                         flush_dcache_mmap_unlock(mapping);
 448                         mutex_unlock(&mapping->i_mmap_mutex);
 449                 }
 450
 451                 /*
 452                  * Clear hugetlb-related page reserves for children. This only
 453                  * affects MAP_PRIVATE mappings. Faults generated by the child
 454                  * are not guaranteed to succeed, even if read-only
 455                  */
 456                 if (is_vm_hugetlb_page(tmp))
 457                         reset_vma_resv_huge_pages(tmp);
 458
 459                 /*
 460                  * Link in the new vma and copy the page table entries.
 461                  */
 462                 *pprev = tmp;
 463                 pprev = &tmp->vm_next;
 464                 tmp->vm_prev = prev;
 465                 prev = tmp;
 466
 467                 __vma_link_rb(mm, tmp, rb_link, rb_parent);
 468                 rb_link = &tmp->vm_rb.rb_right;
 469                 rb_parent = &tmp->vm_rb;
 470
 471                 mm->map_count++;
 472                 retval = copy_page_range(mm, oldmm, mpnt);
 473
 474                 if (tmp->vm_ops && tmp->vm_ops->open)
 475                         tmp->vm_ops->open(tmp);
 476
 477                 if (retval)
 478                         goto out;
 479         }
 480         /* a new mm has just been created */
 481         arch_dup_mmap(oldmm, mm);
 482         retval = 0;
 483 out:
 484         up_write(&mm->mmap_sem);
 485         flush_tlb_mm(oldmm);
 486         up_write(&oldmm->mmap_sem);
 487         uprobe_end_dup_mmap();
 488         return retval;
 489 fail_nomem_anon_vma_fork:
 490         mpol_put(vma_policy(tmp));
 491 fail_nomem_policy:
 492         kmem_cache_free(vm_area_cachep, tmp);
 493 fail_nomem:
 494         retval = -ENOMEM;
 495         vm_unacct_memory(charge);
 496         goto out;
 497 }
 498
 499 static inline int mm_alloc_pgd(struct mm_struct *mm)
 500 {
 501         mm->pgd = pgd_alloc(mm);
 502         if (unlikely(!mm->pgd))
 503                 return -ENOMEM;
 504         return 0;
 505 }
 506
 507 static inline void mm_free_pgd(struct mm_struct *mm)
 508 {
 509         pgd_free(mm, mm->pgd);
 510 }
 511 #else
 512 #define dup_mmap(mm, oldmm)     (0)
 513 #define mm_alloc_pgd(mm)        (0)
 514 #define mm_free_pgd(mm)
 515 #endif /* CONFIG_MMU */
 516
 517 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
 518
 519 #define allocate_mm()   (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
 520 #define free_mm(mm)     (kmem_cache_free(mm_cachep, (mm)))
 521
 522 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
 523
 524 static int __init coredump_filter_setup(char *s)
 525 {
 526         default_dump_filter =
 527                 (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
 528                 MMF_DUMP_FILTER_MASK;
 529         return 1;
 530 }
 531
 532 __setup("coredump_filter=", coredump_filter_setup);
 533
 534 #include <linux/init_task.h>
 535
 536 static void mm_init_aio(struct mm_struct *mm)
 537 {
 538 #ifdef CONFIG_AIO
 539         spin_lock_init(&mm->ioctx_lock);
 540         mm->ioctx_table = NULL;
 541 #endif
 542 }
 543
 544 static void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
 545 {
 546 #ifdef CONFIG_MEMCG
 547         mm->owner = p;
 548 #endif
 549 }
 550
 551 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
 552 {
 553         mm->mmap = NULL;
 554         mm->mm_rb = RB_ROOT;
 555         mm->vmacache_seqnum = 0;
 556         atomic_set(&mm->mm_users, 1);
 557         atomic_set(&mm->mm_count, 1);
 558         init_rwsem(&mm->mmap_sem);
 559         INIT_LIST_HEAD(&mm->mmlist);
 560         mm->core_state = NULL;
 561         atomic_long_set(&mm->nr_ptes, 0);
 562         mm->map_count = 0;
 563         mm->locked_vm = 0;
 564         mm->pinned_vm = 0;
 565         memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
 566         spin_lock_init(&mm->page_table_lock);
 567         mm_init_cpumask(mm);
 568         mm_init_aio(mm);
 569         mm_init_owner(mm, p);
 570         mmu_notifier_mm_init(mm);
 571         clear_tlb_flush_pending(mm);
 572 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
 573         mm->pmd_huge_pte = NULL;
 574 #endif
 575
 576         if (current->mm) {
 577                 mm->flags = current->mm->flags & MMF_INIT_MASK;
 578                 mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
 579         } else {
 580                 mm->flags = default_dump_filter;
 581                 mm->def_flags = 0;
 582         }
 583
 584         if (mm_alloc_pgd(mm))
 585                 goto fail_nopgd;
 586
 587         if (init_new_context(p, mm))
 588                 goto fail_nocontext;
 589
 590         return mm;
 591
 592 fail_nocontext:
 593         mm_free_pgd(mm);
 594 fail_nopgd:
 595         free_mm(mm);
 596         return NULL;
 597 }
 598
 599 static void check_mm(struct mm_struct *mm)
 600 {
 601         int i;
 602
 603         for (i = 0; i < NR_MM_COUNTERS; i++) {
 604                 long x = atomic_long_read(&mm->rss_stat.count[i]);
 605
 606                 if (unlikely(x))
 607                         printk(KERN_ALERT "BUG: Bad rss-counter state "
 608                                           "mm:%p idx:%d val:%ld\n", mm, i, x);
 609         }
 610 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
 611         VM_BUG_ON_MM(mm->pmd_huge_pte, mm);
 612 #endif
 613 }
 614
 615 /*
 616  * Allocate and initialize an mm_struct.
 617  */
 618 struct mm_struct *mm_alloc(void)
 619 {
 620         struct mm_struct *mm;
 621
 622         mm = allocate_mm();
 623         if (!mm)
 624                 return NULL;
 625
 626         memset(mm, 0, sizeof(*mm));
 627         return mm_init(mm, current);
 628 }
 629
 630 /*
 631  * Called when the last reference to the mm
 632  * is dropped: either by a lazy thread or by
 633  * mmput. Free the page directory and the mm.
 634  */
 635 void __mmdrop(struct mm_struct *mm)
 636 {
 637         BUG_ON(mm == &init_mm);
 638         mm_free_pgd(mm);
 639         destroy_context(mm);
 640         mmu_notifier_mm_destroy(mm);
 641         check_mm(mm);
 642         free_mm(mm);
 643 }
 644 EXPORT_SYMBOL_GPL(__mmdrop);
 645
 646 /*
 647  * Decrement the use count and release all resources for an mm.
 648  */
 649 void mmput(struct mm_struct *mm)
 650 {
 651         might_sleep();
 652
 653         if (atomic_dec_and_test(&mm->mm_users)) {
 654                 uprobe_clear_state(mm);
 655                 exit_aio(mm);
 656                 ksm_exit(mm);
 657                 khugepaged_exit(mm); /* must run before exit_mmap */
 658                 exit_mmap(mm);
 659                 set_mm_exe_file(mm, NULL);
 660                 if (!list_empty(&mm->mmlist)) {
 661                         spin_lock(&mmlist_lock);
 662                         list_del(&mm->mmlist);
 663                         spin_unlock(&mmlist_lock);
 664                 }
 665                 if (mm->binfmt)
 666                         module_put(mm->binfmt->module);
 667                 mmdrop(mm);
 668         }
 669 }
 670 EXPORT_SYMBOL_GPL(mmput);
 671
 672 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
 673 {
 674         if (new_exe_file)
 675                 get_file(new_exe_file);
 676         if (mm->exe_file)
 677                 fput(mm->exe_file);
 678         mm->exe_file = new_exe_file;
 679 }
 680
 681 struct file *get_mm_exe_file(struct mm_struct *mm)
 682 {
 683         struct file *exe_file;
 684
 685         /* We need mmap_sem to protect against races with removal of exe_file */
 686         down_read(&mm->mmap_sem);
 687         exe_file = mm->exe_file;
 688         if (exe_file)
 689                 get_file(exe_file);
 690         up_read(&mm->mmap_sem);
 691         return exe_file;
 692 }
 693
 694 static void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
 695 {
 696         /* It's safe to write the exe_file pointer without exe_file_lock because
 697          * this is called during fork when the task is not yet in /proc */
 698         newmm->exe_file = get_mm_exe_file(oldmm);
 699 }
 700
 701 /**
 702  * get_task_mm - acquire a reference to the task's mm
 703  *
 704  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
 705  * this kernel workthread has transiently adopted a user mm with use_mm,
 706  * to do its AIO) is not set and if so returns a reference to it, after
 707  * bumping up the use count.  User must release the mm via mmput()
 708  * after use.  Typically used by /proc and ptrace.
 709  */
 710 struct mm_struct *get_task_mm(struct task_struct *task)
 711 {
 712         struct mm_struct *mm;
 713
 714         task_lock(task);
 715         mm = task->mm;
 716         if (mm) {
 717                 if (task->flags & PF_KTHREAD)
 718                         mm = NULL;
 719                 else
 720                         atomic_inc(&mm->mm_users);
 721         }
 722         task_unlock(task);
 723         return mm;
 724 }
 725 EXPORT_SYMBOL_GPL(get_task_mm);
 726
 727 struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
 728 {
 729         struct mm_struct *mm;
 730         int err;
 731
 732         err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
 733         if (err)
 734                 return ERR_PTR(err);
 735
 736         mm = get_task_mm(task);
 737         if (mm && mm != current->mm &&
 738                         !ptrace_may_access(task, mode)) {
 739                 mmput(mm);
 740                 mm = ERR_PTR(-EACCES);
 741         }
 742         mutex_unlock(&task->signal->cred_guard_mutex);
 743
 744         return mm;
 745 }
 746
 747 static void complete_vfork_done(struct task_struct *tsk)
 748 {
 749         struct completion *vfork;
 750
 751         task_lock(tsk);
 752         vfork = tsk->vfork_done;
 753         if (likely(vfork)) {
 754                 tsk->vfork_done = NULL;
 755                 complete(vfork);
 756         }
 757         task_unlock(tsk);
 758 }
 759
 760 static int wait_for_vfork_done(struct task_struct *child,
 761                                 struct completion *vfork)
 762 {
 763         int killed;
 764
 765         freezer_do_not_count();
 766         killed = wait_for_completion_killable(vfork);
 767         freezer_count();
 768
 769         if (killed) {
 770                 task_lock(child);
 771                 child->vfork_done = NULL;
 772                 task_unlock(child);
 773         }
 774
 775         put_task_struct(child);
 776         return killed;
 777 }
 778
 779 /* Please note the differences between mmput and mm_release.
 780  * mmput is called whenever we stop holding onto a mm_struct,
 781  * error success whatever.
 782  *
 783  * mm_release is called after a mm_struct has been removed
 784  * from the current process.
 785  *
 786  * This difference is important for error handling, when we
 787  * only half set up a mm_struct for a new process and need to restore
 788  * the old one.  Because we mmput the new mm_struct before
 789  * restoring the old one. . .
 790  * Eric Biederman 10 January 1998
 791  */
 792 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
 793 {
 794         /* Get rid of any futexes when releasing the mm */
 795 #ifdef CONFIG_FUTEX
 796         if (unlikely(tsk->robust_list)) {
 797                 exit_robust_list(tsk);
 798                 tsk->robust_list = NULL;
 799         }
 800 #ifdef CONFIG_COMPAT
 801         if (unlikely(tsk->compat_robust_list)) {
 802                 compat_exit_robust_list(tsk);
 803                 tsk->compat_robust_list = NULL;
 804         }
 805 #endif
 806         if (unlikely(!list_empty(&tsk->pi_state_list)))
 807                 exit_pi_state_list(tsk);
 808 #endif
 809
 810         uprobe_free_utask(tsk);
 811
 812         /* Get rid of any cached register state */
 813         deactivate_mm(tsk, mm);
 814
 815         /*
 816          * If we're exiting normally, clear a user-space tid field if
 817          * requested.  We leave this alone when dying by signal, to leave
 818          * the value intact in a core dump, and to save the unnecessary
 819          * trouble, say, a killed vfork parent shouldn't touch this mm.
 820          * Userland only wants this done for a sys_exit.
 821          */
 822         if (tsk->clear_child_tid) {
 823                 if (!(tsk->flags & PF_SIGNALED) &&
 824                     atomic_read(&mm->mm_users) > 1) {
 825                         /*
 826                          * We don't check the error code - if userspace has
 827                          * not set up a proper pointer then tough luck.
 828                          */
 829                         put_user(0, tsk->clear_child_tid);
 830                         sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
 831                                         1, NULL, NULL, 0);
 832                 }
 833                 tsk->clear_child_tid = NULL;
 834         }
 835
 836         /*
 837          * All done, finally we can wake up parent and return this mm to him.
 838          * Also kthread_stop() uses this completion for synchronization.
 839          */
 840         if (tsk->vfork_done)
 841                 complete_vfork_done(tsk);
 842 }
 843
 844 /*
 845  * Allocate a new mm structure and copy contents from the
 846  * mm structure of the passed in task structure.
 847  */
 848 static struct mm_struct *dup_mm(struct task_struct *tsk)
 849 {
 850         struct mm_struct *mm, *oldmm = current->mm;
 851         int err;
 852
 853         mm = allocate_mm();
 854         if (!mm)
 855                 goto fail_nomem;
 856
 857         memcpy(mm, oldmm, sizeof(*mm));
 858
 859         if (!mm_init(mm, tsk))
 860                 goto fail_nomem;
 861
 862         dup_mm_exe_file(oldmm, mm);
 863
 864         err = dup_mmap(mm, oldmm);
 865         if (err)
 866                 goto free_pt;
 867
 868         mm->hiwater_rss = get_mm_rss(mm);
 869         mm->hiwater_vm = mm->total_vm;
 870
 871         if (mm->binfmt && !try_module_get(mm->binfmt->module))
 872                 goto free_pt;
 873
 874         return mm;
 875
 876 free_pt:
 877         /* don't put binfmt in mmput, we haven't got module yet */
 878         mm->binfmt = NULL;
 879         mmput(mm);
 880
 881 fail_nomem:
 882         return NULL;
 883 }
 884
 885 static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
 886 {
 887         struct mm_struct *mm, *oldmm;
 888         int retval;
 889
 890         tsk->min_flt = tsk->maj_flt = 0;
 891         tsk->nvcsw = tsk->nivcsw = 0;
 892 #ifdef CONFIG_DETECT_HUNG_TASK
 893         tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
 894 #endif
 895
 896         tsk->mm = NULL;
 897         tsk->active_mm = NULL;
 898
 899         /*
 900          * Are we cloning a kernel thread?
 901          *
 902          * We need to steal a active VM for that..
 903          */
 904         oldmm = current->mm;
 905         if (!oldmm)
 906                 return 0;
 907
 908         /* initialize the new vmacache entries */
 909         vmacache_flush(tsk);
 910
 911         if (clone_flags & CLONE_VM) {
 912                 atomic_inc(&oldmm->mm_users);
 913                 mm = oldmm;
 914                 goto good_mm;
 915         }
 916
 917         retval = -ENOMEM;
 918         mm = dup_mm(tsk);
 919         if (!mm)
 920                 goto fail_nomem;
 921
 922 good_mm:
 923         tsk->mm = mm;
 924         tsk->active_mm = mm;
 925         return 0;
 926
 927 fail_nomem:
 928         return retval;
 929 }
 930
 931 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
 932 {
 933         struct fs_struct *fs = current->fs;
 934         if (clone_flags & CLONE_FS) {
 935                 /* tsk->fs is already what we want */
 936                 spin_lock(&fs->lock);
 937                 if (fs->in_exec) {
 938                         spin_unlock(&fs->lock);
 939                         return -EAGAIN;
 940                 }
 941                 fs->users++;
 942                 spin_unlock(&fs->lock);
 943                 return 0;
 944         }
 945         tsk->fs = copy_fs_struct(fs);
 946         if (!tsk->fs)
 947                 return -ENOMEM;
 948         return 0;
 949 }
 950
 951 static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
 952 {
 953         struct files_struct *oldf, *newf;
 954         int error = 0;
 955
 956         /*
 957          * A background process may not have any files ...
 958          */
 959         oldf = current->files;
 960         if (!oldf)
 961                 goto out;
 962
 963         if (clone_flags & CLONE_FILES) {
 964                 atomic_inc(&oldf->count);
 965                 goto out;
 966         }
 967
 968         newf = dup_fd(oldf, &error);
 969         if (!newf)
 970                 goto out;
 971
 972         tsk->files = newf;
 973         error = 0;
 974 out:
 975         return error;
 976 }
 977
 978 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
 979 {
 980 #ifdef CONFIG_BLOCK
 981         struct io_context *ioc = current->io_context;
 982         struct io_context *new_ioc;
 983
 984         if (!ioc)
 985                 return 0;
 986         /*
 987          * Share io context with parent, if CLONE_IO is set
 988          */
 989         if (clone_flags & CLONE_IO) {
 990                 ioc_task_link(ioc);
 991                 tsk->io_context = ioc;
 992         } else if (ioprio_valid(ioc->ioprio)) {
 993                 new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
 994                 if (unlikely(!new_ioc))
 995                         return -ENOMEM;
 996
 997                 new_ioc->ioprio = ioc->ioprio;
 998                 put_io_context(new_ioc);
 999         }
1000 #endif
1001         return 0;
1002 }
1003
1004 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
1005 {
1006         struct sighand_struct *sig;
1007
1008         if (clone_flags & CLONE_SIGHAND) {
1009                 atomic_inc(&current->sighand->count);
1010                 return 0;
1011         }
1012         sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
1013         rcu_assign_pointer(tsk->sighand, sig);
1014         if (!sig)
1015                 return -ENOMEM;
1016         atomic_set(&sig->count, 1);
1017         memcpy(sig->action, current->sighand->action, sizeof(sig->action));
1018         return 0;
1019 }
1020
1021 void __cleanup_sighand(struct sighand_struct *sighand)
1022 {
1023         if (atomic_dec_and_test(&sighand->count)) {
1024                 signalfd_cleanup(sighand);
1025                 kmem_cache_free(sighand_cachep, sighand);
1026         }
1027 }
1028
1029
1030 /*
1031  * Initialize POSIX timer handling for a thread group.
1032  */
1033 static void posix_cpu_timers_init_group(struct signal_struct *sig)
1034 {
1035         unsigned long cpu_limit;
1036
1037         /* Thread group counters. */
1038         thread_group_cputime_init(sig);
1039
1040         cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1041         if (cpu_limit != RLIM_INFINITY) {
1042                 sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
1043                 sig->cputimer.running = 1;
1044         }
1045
1046         /* The timer lists. */
1047         INIT_LIST_HEAD(&sig->cpu_timers[0]);
1048         INIT_LIST_HEAD(&sig->cpu_timers[1]);
1049         INIT_LIST_HEAD(&sig->cpu_timers[2]);
1050 }
1051
1052 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1053 {
1054         struct signal_struct *sig;
1055
1056         if (clone_flags & CLONE_THREAD)
1057                 return 0;
1058
1059         sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1060         tsk->signal = sig;
1061         if (!sig)
1062                 return -ENOMEM;
1063
1064         sig->nr_threads = 1;
1065         atomic_set(&sig->live, 1);
1066         atomic_set(&sig->sigcnt, 1);
1067
1068         /* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */
1069         sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node);
1070         tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);
1071
1072         init_waitqueue_head(&sig->wait_chldexit);
1073         sig->curr_target = tsk;
1074         init_sigpending(&sig->shared_pending);
1075         INIT_LIST_HEAD(&sig->posix_timers);
1076         seqlock_init(&sig->stats_lock);
1077
1078         hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1079         sig->real_timer.function = it_real_fn;
1080
1081         task_lock(current->group_leader);
1082         memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1083         task_unlock(current->group_leader);
1084
1085         posix_cpu_timers_init_group(sig);
1086
1087         tty_audit_fork(sig);
1088         sched_autogroup_fork(sig);
1089
1090 #ifdef CONFIG_CGROUPS
1091         init_rwsem(&sig->group_rwsem);
1092 #endif
1093
1094         sig->oom_score_adj = current->signal->oom_score_adj;
1095         sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1096
1097         sig->has_child_subreaper = current->signal->has_child_subreaper ||
1098                                    current->signal->is_child_subreaper;
1099
1100         mutex_init(&sig->cred_guard_mutex);
1101
1102         return 0;
1103 }
1104
1105 static void copy_seccomp(struct task_struct *p)
1106 {
1107 #ifdef CONFIG_SECCOMP
1108         /*
1109          * Must be called with sighand->lock held, which is common to
1110          * all threads in the group. Holding cred_guard_mutex is not
1111          * needed because this new task is not yet running and cannot
1112          * be racing exec.
1113          */
1114         assert_spin_locked(&current->sighand->siglock);
1115
1116         /* Ref-count the new filter user, and assign it. */
1117         get_seccomp_filter(current);
1118         p->seccomp = current->seccomp;
1119
1120         /*
1121          * Explicitly enable no_new_privs here in case it got set
1122          * between the task_struct being duplicated and holding the
1123          * sighand lock. The seccomp state and nnp must be in sync.
1124          */
1125         if (task_no_new_privs(current))
1126                 task_set_no_new_privs(p);
1127
1128         /*
1129          * If the parent gained a seccomp mode after copying thread
1130          * flags and between before we held the sighand lock, we have
1131          * to manually enable the seccomp thread flag here.
1132          */
1133         if (p->seccomp.mode != SECCOMP_MODE_DISABLED)
1134                 set_tsk_thread_flag(p, TIF_SECCOMP);
1135 #endif
1136 }
1137
1138 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1139 {
1140         current->clear_child_tid = tidptr;
1141
1142         return task_pid_vnr(current);
1143 }
1144
1145 static void rt_mutex_init_task(struct task_struct *p)
1146 {
1147         raw_spin_lock_init(&p->pi_lock);
1148 #ifdef CONFIG_RT_MUTEXES
1149         p->pi_waiters = RB_ROOT;
1150         p->pi_waiters_leftmost = NULL;
1151         p->pi_blocked_on = NULL;
1152 #endif
1153 }
1154
1155 /*
1156  * Initialize POSIX timer handling for a single task.
1157  */
1158 static void posix_cpu_timers_init(struct task_struct *tsk)
1159 {
1160         tsk->cputime_expires.prof_exp = 0;
1161         tsk->cputime_expires.virt_exp = 0;
1162         tsk->cputime_expires.sched_exp = 0;
1163         INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1164         INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1165         INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1166 }
1167
1168 static inline void
1169 init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
1170 {
1171          task->pids[type].pid = pid;
1172 }
1173
1174 /*
1175  * This creates a new process as a copy of the old one,
1176  * but does not actually start it yet.
1177  *
1178  * It copies the registers, and all the appropriate
1179  * parts of the process environment (as per the clone
1180  * flags). The actual kick-off is left to the caller.
1181  */
1182 static struct task_struct *copy_process(unsigned long clone_flags,
1183                                         unsigned long stack_start,
1184                                         unsigned long stack_size,
1185                                         int __user *child_tidptr,
1186                                         struct pid *pid,
1187                                         int trace)
1188 {
1189         int retval;
1190         struct task_struct *p;
1191
1192         if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1193                 return ERR_PTR(-EINVAL);
1194
1195         if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
1196                 return ERR_PTR(-EINVAL);
1197
1198         /*
1199          * Thread groups must share signals as well, and detached threads
1200          * can only be started up within the thread group.
1201          */
1202         if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1203                 return ERR_PTR(-EINVAL);
1204
1205         /*
1206          * Shared signal handlers imply shared VM. By way of the above,
1207          * thread groups also imply shared VM. Blocking this case allows
1208          * for various simplifications in other code.
1209          */
1210         if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1211                 return ERR_PTR(-EINVAL);
1212
1213         /*
1214          * Siblings of global init remain as zombies on exit since they are
1215          * not reaped by their parent (swapper). To solve this and to avoid
1216          * multi-rooted process trees, prevent global and container-inits
1217          * from creating siblings.
1218          */
1219         if ((clone_flags & CLONE_PARENT) &&
1220                                 current->signal->flags & SIGNAL_UNKILLABLE)
1221                 return ERR_PTR(-EINVAL);
1222
1223         /*
1224          * If the new process will be in a different pid or user namespace
1225          * do not allow it to share a thread group or signal handlers or
1226          * parent with the forking task.
1227          */
1228         if (clone_flags & CLONE_SIGHAND) {
1229                 if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
1230                     (task_active_pid_ns(current) !=
1231                                 current->nsproxy->pid_ns_for_children))
1232                         return ERR_PTR(-EINVAL);
1233         }
1234
1235         retval = security_task_create(clone_flags);
1236         if (retval)
1237                 goto fork_out;
1238
1239         retval = -ENOMEM;
1240         p = dup_task_struct(current);
1241         if (!p)
1242                 goto fork_out;
1243
1244         ftrace_graph_init_task(p);
1245
1246         rt_mutex_init_task(p);
1247
1248 #ifdef CONFIG_PROVE_LOCKING
1249         DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1250         DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1251 #endif
1252         retval = -EAGAIN;
1253         if (atomic_read(&p->real_cred->user->processes) >=
1254                         task_rlimit(p, RLIMIT_NPROC)) {
1255                 if (p->real_cred->user != INIT_USER &&
1256                     !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
1257                         goto bad_fork_free;
1258         }
1259         current->flags &= ~PF_NPROC_EXCEEDED;
1260
1261         retval = copy_creds(p, clone_flags);
1262         if (retval < 0)
1263                 goto bad_fork_free;
1264
1265         /*
1266          * If multiple threads are within copy_process(), then this check
1267          * triggers too late. This doesn't hurt, the check is only there
1268          * to stop root fork bombs.
1269          */
1270         retval = -EAGAIN;
1271         if (nr_threads >= max_threads)
1272                 goto bad_fork_cleanup_count;
1273
1274         if (!try_module_get(task_thread_info(p)->exec_domain->module))
1275                 goto bad_fork_cleanup_count;
1276
1277         delayacct_tsk_init(p);  /* Must remain after dup_task_struct() */
1278         p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
1279         p->flags |= PF_FORKNOEXEC;
1280         INIT_LIST_HEAD(&p->children);
1281         INIT_LIST_HEAD(&p->sibling);
1282         rcu_copy_process(p);
1283         p->vfork_done = NULL;
1284         spin_lock_init(&p->alloc_lock);
1285
1286         init_sigpending(&p->pending);
1287
1288         p->utime = p->stime = p->gtime = 0;
1289         p->utimescaled = p->stimescaled = 0;
1290 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
1291         p->prev_cputime.utime = p->prev_cputime.stime = 0;
1292 #endif
1293 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
1294         seqlock_init(&p->vtime_seqlock);
1295         p->vtime_snap = 0;
1296         p->vtime_snap_whence = VTIME_SLEEPING;
1297 #endif
1298
1299 #if defined(SPLIT_RSS_COUNTING)
1300         memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1301 #endif
1302
1303         p->default_timer_slack_ns = current->timer_slack_ns;
1304
1305         task_io_accounting_init(&p->ioac);
1306         acct_clear_integrals(p);
1307
1308         posix_cpu_timers_init(p);
1309
1310         p->start_time = ktime_get_ns();
1311         p->real_start_time = ktime_get_boot_ns();
1312         p->io_context = NULL;
1313         p->audit_context = NULL;
1314         if (clone_flags & CLONE_THREAD)
1315                 threadgroup_change_begin(current);
1316         cgroup_fork(p);
1317 #ifdef CONFIG_NUMA
1318         p->mempolicy = mpol_dup(p->mempolicy);
1319         if (IS_ERR(p->mempolicy)) {
1320                 retval = PTR_ERR(p->mempolicy);
1321                 p->mempolicy = NULL;
1322                 goto bad_fork_cleanup_threadgroup_lock;
1323         }
1324 #endif
1325 #ifdef CONFIG_CPUSETS
1326         p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
1327         p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
1328         seqcount_init(&p->mems_allowed_seq);
1329 #endif
1330 #ifdef CONFIG_TRACE_IRQFLAGS
1331         p->irq_events = 0;
1332         p->hardirqs_enabled = 0;
1333         p->hardirq_enable_ip = 0;
1334         p->hardirq_enable_event = 0;
1335         p->hardirq_disable_ip = _THIS_IP_;
1336         p->hardirq_disable_event = 0;
1337         p->softirqs_enabled = 1;
1338         p->softirq_enable_ip = _THIS_IP_;
1339         p->softirq_enable_event = 0;
1340         p->softirq_disable_ip = 0;
1341         p->softirq_disable_event = 0;
1342         p->hardirq_context = 0;
1343         p->softirq_context = 0;
1344 #endif
1345 #ifdef CONFIG_LOCKDEP
1346         p->lockdep_depth = 0; /* no locks held yet */
1347         p->curr_chain_key = 0;
1348         p->lockdep_recursion = 0;
1349 #endif
1350
1351 #ifdef CONFIG_DEBUG_MUTEXES
1352         p->blocked_on = NULL; /* not blocked yet */
1353 #endif
1354 #ifdef CONFIG_BCACHE
1355         p->sequential_io        = 0;
1356         p->sequential_io_avg    = 0;
1357 #endif
1358
1359         /* Perform scheduler related setup. Assign this task to a CPU. */
1360         retval = sched_fork(clone_flags, p);
1361         if (retval)
1362                 goto bad_fork_cleanup_policy;
1363
1364         retval = perf_event_init_task(p);
1365         if (retval)
1366                 goto bad_fork_cleanup_policy;
1367         retval = audit_alloc(p);
1368         if (retval)
1369                 goto bad_fork_cleanup_perf;
1370         /* copy all the process information */
1371         shm_init_task(p);
1372         retval = copy_semundo(clone_flags, p);
1373         if (retval)
1374                 goto bad_fork_cleanup_audit;
1375         retval = copy_files(clone_flags, p);
1376         if (retval)
1377                 goto bad_fork_cleanup_semundo;
1378         retval = copy_fs(clone_flags, p);
1379         if (retval)
1380                 goto bad_fork_cleanup_files;
1381         retval = copy_sighand(clone_flags, p);
1382         if (retval)
1383                 goto bad_fork_cleanup_fs;
1384         retval = copy_signal(clone_flags, p);
1385         if (retval)
1386                 goto bad_fork_cleanup_sighand;
1387         retval = copy_mm(clone_flags, p);
1388         if (retval)
1389                 goto bad_fork_cleanup_signal;
1390         retval = copy_namespaces(clone_flags, p);
1391         if (retval)
1392                 goto bad_fork_cleanup_mm;
1393         retval = copy_io(clone_flags, p);
1394         if (retval)
1395                 goto bad_fork_cleanup_namespaces;
1396         retval = copy_thread(clone_flags, stack_start, stack_size, p);
1397         if (retval)
1398                 goto bad_fork_cleanup_io;
1399
1400         if (pid != &init_struct_pid) {
1401                 retval = -ENOMEM;
1402                 pid = alloc_pid(p->nsproxy->pid_ns_for_children);
1403                 if (!pid)
1404                         goto bad_fork_cleanup_io;
1405         }
1406
1407         p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1408         /*
1409          * Clear TID on mm_release()?
1410          */
1411         p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
1412 #ifdef CONFIG_BLOCK
1413         p->plug = NULL;
1414 #endif
1415 #ifdef CONFIG_FUTEX
1416         p->robust_list = NULL;
1417 #ifdef CONFIG_COMPAT
1418         p->compat_robust_list = NULL;
1419 #endif
1420         INIT_LIST_HEAD(&p->pi_state_list);
1421         p->pi_state_cache = NULL;
1422 #endif
1423         /*
1424          * sigaltstack should be cleared when sharing the same VM
1425          */
1426         if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1427                 p->sas_ss_sp = p->sas_ss_size = 0;
1428
1429         /*
1430          * Syscall tracing and stepping should be turned off in the
1431          * child regardless of CLONE_PTRACE.
1432          */
1433         user_disable_single_step(p);
1434         clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1435 #ifdef TIF_SYSCALL_EMU
1436         clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1437 #endif
1438         clear_all_latency_tracing(p);
1439
1440         /* ok, now we should be set up.. */
1441         p->pid = pid_nr(pid);
1442         if (clone_flags & CLONE_THREAD) {
1443                 p->exit_signal = -1;
1444                 p->group_leader = current->group_leader;
1445                 p->tgid = current->tgid;
1446         } else {
1447                 if (clone_flags & CLONE_PARENT)
1448                         p->exit_signal = current->group_leader->exit_signal;
1449                 else
1450                         p->exit_signal = (clone_flags & CSIGNAL);
1451                 p->group_leader = p;
1452                 p->tgid = p->pid;
1453         }
1454
1455         p->nr_dirtied = 0;
1456         p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
1457         p->dirty_paused_when = 0;
1458
1459         p->pdeath_signal = 0;
1460         INIT_LIST_HEAD(&p->thread_group);
1461         p->task_works = NULL;
1462
1463         /*
1464          * Make it visible to the rest of the system, but dont wake it up yet.
1465          * Need tasklist lock for parent etc handling!
1466          */
1467         write_lock_irq(&tasklist_lock);
1468
1469         /* CLONE_PARENT re-uses the old parent */
1470         if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1471                 p->real_parent = current->real_parent;
1472                 p->parent_exec_id = current->parent_exec_id;
1473         } else {
1474                 p->real_parent = current;
1475                 p->parent_exec_id = current->self_exec_id;
1476         }
1477
1478         spin_lock(&current->sighand->siglock);
1479
1480         /*
1481          * Copy seccomp details explicitly here, in case they were changed
1482          * before holding sighand lock.
1483          */
1484         copy_seccomp(p);
1485
1486         /*
1487          * Process group and session signals need to be delivered to just the
1488          * parent before the fork or both the parent and the child after the
1489          * fork. Restart if a signal comes in before we add the new process to
1490          * it's process group.
1491          * A fatal signal pending means that current will exit, so the new
1492          * thread can't slip out of an OOM kill (or normal SIGKILL).
1493         */
1494         recalc_sigpending();
1495         if (signal_pending(current)) {
1496                 spin_unlock(&current->sighand->siglock);
1497                 write_unlock_irq(&tasklist_lock);
1498                 retval = -ERESTARTNOINTR;
1499                 goto bad_fork_free_pid;
1500         }
1501
1502         if (likely(p->pid)) {
1503                 ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
1504
1505                 init_task_pid(p, PIDTYPE_PID, pid);
1506                 if (thread_group_leader(p)) {
1507                         init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
1508                         init_task_pid(p, PIDTYPE_SID, task_session(current));
1509
1510                         if (is_child_reaper(pid)) {
1511                                 ns_of_pid(pid)->child_reaper = p;
1512                                 p->signal->flags |= SIGNAL_UNKILLABLE;
1513                         }
1514
1515                         p->signal->leader_pid = pid;
1516                         p->signal->tty = tty_kref_get(current->signal->tty);
1517                         list_add_tail(&p->sibling, &p->real_parent->children);
1518                         list_add_tail_rcu(&p->tasks, &init_task.tasks);
1519                         attach_pid(p, PIDTYPE_PGID);
1520                         attach_pid(p, PIDTYPE_SID);
1521                         __this_cpu_inc(process_counts);
1522                 } else {
1523                         current->signal->nr_threads++;
1524                         atomic_inc(&current->signal->live);
1525                         atomic_inc(&current->signal->sigcnt);
1526                         list_add_tail_rcu(&p->thread_group,
1527                                           &p->group_leader->thread_group);
1528                         list_add_tail_rcu(&p->thread_node,
1529                                           &p->signal->thread_head);
1530                 }
1531                 attach_pid(p, PIDTYPE_PID);
1532                 nr_threads++;
1533         }
1534
1535         total_forks++;
1536         spin_unlock(&current->sighand->siglock);
1537         syscall_tracepoint_update(p);
1538         write_unlock_irq(&tasklist_lock);
1539
1540         proc_fork_connector(p);
1541         cgroup_post_fork(p);
1542         if (clone_flags & CLONE_THREAD)
1543                 threadgroup_change_end(current);
1544         perf_event_fork(p);
1545
1546         trace_task_newtask(p, clone_flags);
1547         uprobe_copy_process(p, clone_flags);
1548
1549         return p;
1550
1551 bad_fork_free_pid:
1552         if (pid != &init_struct_pid)
1553                 free_pid(pid);
1554 bad_fork_cleanup_io:
1555         if (p->io_context)
1556                 exit_io_context(p);
1557 bad_fork_cleanup_namespaces:
1558         exit_task_namespaces(p);
1559 bad_fork_cleanup_mm:
1560         if (p->mm)
1561                 mmput(p->mm);
1562 bad_fork_cleanup_signal:
1563         if (!(clone_flags & CLONE_THREAD))
1564                 free_signal_struct(p->signal);
1565 bad_fork_cleanup_sighand:
1566         __cleanup_sighand(p->sighand);
1567 bad_fork_cleanup_fs:
1568         exit_fs(p); /* blocking */
1569 bad_fork_cleanup_files:
1570         exit_files(p); /* blocking */
1571 bad_fork_cleanup_semundo:
1572         exit_sem(p);
1573 bad_fork_cleanup_audit:
1574         audit_free(p);
1575 bad_fork_cleanup_perf:
1576         perf_event_free_task(p);
1577 bad_fork_cleanup_policy:
1578 #ifdef CONFIG_NUMA
1579         mpol_put(p->mempolicy);
1580 bad_fork_cleanup_threadgroup_lock:
1581 #endif
1582         if (clone_flags & CLONE_THREAD)
1583                 threadgroup_change_end(current);
1584         delayacct_tsk_free(p);
1585         module_put(task_thread_info(p)->exec_domain->module);
1586 bad_fork_cleanup_count:
1587         atomic_dec(&p->cred->user->processes);
1588         exit_creds(p);
1589 bad_fork_free:
1590         free_task(p);
1591 fork_out:
1592         return ERR_PTR(retval);
1593 }
1594
1595 static inline void init_idle_pids(struct pid_link *links)
1596 {
1597         enum pid_type type;
1598
1599         for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1600                 INIT_HLIST_NODE(&links[type].node); /* not really needed */
1601                 links[type].pid = &init_struct_pid;
1602         }
1603 }
1604
1605 struct task_struct *fork_idle(int cpu)
1606 {
1607         struct task_struct *task;
1608         task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0);
1609         if (!IS_ERR(task)) {
1610                 init_idle_pids(task->pids);
1611                 init_idle(task, cpu);
1612         }
1613
1614         return task;
1615 }
1616
1617 /*
1618  *  Ok, this is the main fork-routine.
1619  *
1620  * It copies the process, and if successful kick-starts
1621  * it and waits for it to finish using the VM if required.
1622  */
1623 long do_fork(unsigned long clone_flags,
1624               unsigned long stack_start,
1625               unsigned long stack_size,
1626               int __user *parent_tidptr,
1627               int __user *child_tidptr)
1628 {
1629         struct task_struct *p;
1630         int trace = 0;
1631         long nr;
1632
1633         /*
1634          * Determine whether and which event to report to ptracer.  When
1635          * called from kernel_thread or CLONE_UNTRACED is explicitly
1636          * requested, no event is reported; otherwise, report if the event
1637          * for the type of forking is enabled.
1638          */
1639         if (!(clone_flags & CLONE_UNTRACED)) {
1640                 if (clone_flags & CLONE_VFORK)
1641                         trace = PTRACE_EVENT_VFORK;
1642                 else if ((clone_flags & CSIGNAL) != SIGCHLD)
1643                         trace = PTRACE_EVENT_CLONE;
1644                 else
1645                         trace = PTRACE_EVENT_FORK;
1646
1647                 if (likely(!ptrace_event_enabled(current, trace)))
1648                         trace = 0;
1649         }
1650
1651         p = copy_process(clone_flags, stack_start, stack_size,
1652                          child_tidptr, NULL, trace);
1653         /*
1654          * Do this prior waking up the new thread - the thread pointer
1655          * might get invalid after that point, if the thread exits quickly.
1656          */
1657         if (!IS_ERR(p)) {
1658                 struct completion vfork;
1659                 struct pid *pid;
1660
1661                 trace_sched_process_fork(current, p);
1662
1663                 pid = get_task_pid(p, PIDTYPE_PID);
1664                 nr = pid_vnr(pid);
1665
1666                 if (clone_flags & CLONE_PARENT_SETTID)
1667                         put_user(nr, parent_tidptr);
1668
1669                 if (clone_flags & CLONE_VFORK) {
1670                         p->vfork_done = &vfork;
1671                         init_completion(&vfork);
1672                         get_task_struct(p);
1673                 }
1674
1675                 wake_up_new_task(p);
1676
1677                 /* forking complete and child started to run, tell ptracer */
1678                 if (unlikely(trace))
1679                         ptrace_event_pid(trace, pid);
1680
1681                 if (clone_flags & CLONE_VFORK) {
1682                         if (!wait_for_vfork_done(p, &vfork))
1683                                 ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
1684                 }
1685
1686                 put_pid(pid);
1687         } else {
1688                 nr = PTR_ERR(p);
1689         }
1690         return nr;
1691 }
1692
1693 /*
1694  * Create a kernel thread.
1695  */
1696 pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
1697 {
1698         return do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
1699                 (unsigned long)arg, NULL, NULL);
1700 }
1701
1702 #ifdef __ARCH_WANT_SYS_FORK
1703 SYSCALL_DEFINE0(fork)
1704 {
1705 #ifdef CONFIG_MMU
1706         return do_fork(SIGCHLD, 0, 0, NULL, NULL);
1707 #else
1708         /* can not support in nommu mode */
1709         return -EINVAL;
1710 #endif
1711 }
1712 #endif
1713
1714 #ifdef __ARCH_WANT_SYS_VFORK
1715 SYSCALL_DEFINE0(vfork)
1716 {
1717         return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0,
1718                         0, NULL, NULL);
1719 }
1720 #endif
1721
1722 #ifdef __ARCH_WANT_SYS_CLONE
1723 #ifdef CONFIG_CLONE_BACKWARDS
1724 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1725                  int __user *, parent_tidptr,
1726                  int, tls_val,
1727                  int __user *, child_tidptr)
1728 #elif defined(CONFIG_CLONE_BACKWARDS2)
1729 SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
1730                  int __user *, parent_tidptr,
1731                  int __user *, child_tidptr,
1732                  int, tls_val)
1733 #elif defined(CONFIG_CLONE_BACKWARDS3)
1734 SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
1735                 int, stack_size,
1736                 int __user *, parent_tidptr,
1737                 int __user *, child_tidptr,
1738                 int, tls_val)
1739 #else
1740 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1741                  int __user *, parent_tidptr,
1742                  int __user *, child_tidptr,
1743                  int, tls_val)
1744 #endif
1745 {
1746         return do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr);
1747 }
1748 #endif
1749
1750 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1751 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1752 #endif
1753
1754 static void sighand_ctor(void *data)
1755 {
1756         struct sighand_struct *sighand = data;
1757
1758         spin_lock_init(&sighand->siglock);
1759         init_waitqueue_head(&sighand->signalfd_wqh);
1760 }
1761
1762 void __init proc_caches_init(void)
1763 {
1764         sighand_cachep = kmem_cache_create("sighand_cache",
1765                         sizeof(struct sighand_struct), 0,
1766                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1767                         SLAB_NOTRACK, sighand_ctor);
1768         signal_cachep = kmem_cache_create("signal_cache",
1769                         sizeof(struct signal_struct), 0,
1770                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1771         files_cachep = kmem_cache_create("files_cache",
1772                         sizeof(struct files_struct), 0,
1773                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1774         fs_cachep = kmem_cache_create("fs_cache",
1775                         sizeof(struct fs_struct), 0,
1776                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1777         /*
1778          * FIXME! The "sizeof(struct mm_struct)" currently includes the
1779          * whole struct cpumask for the OFFSTACK case. We could change
1780          * this to *only* allocate as much of it as required by the
1781          * maximum number of CPU's we can ever have.  The cpumask_allocation
1782          * is at the end of the structure, exactly for that reason.
1783          */
1784         mm_cachep = kmem_cache_create("mm_struct",
1785                         sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1786                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1787         vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1788         mmap_init();
1789         nsproxy_cache_init();
1790 }
1791
1792 /*
1793  * Check constraints on flags passed to the unshare system call.
1794  */
1795 static int check_unshare_flags(unsigned long unshare_flags)
1796 {
1797         if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1798                                 CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1799                                 CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
1800                                 CLONE_NEWUSER|CLONE_NEWPID))
1801                 return -EINVAL;
1802         /*
1803          * Not implemented, but pretend it works if there is nothing to
1804          * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
1805          * needs to unshare vm.
1806          */
1807         if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
1808                 /* FIXME: get_task_mm() increments ->mm_users */
1809                 if (atomic_read(&current->mm->mm_users) > 1)
1810                         return -EINVAL;
1811         }
1812
1813         return 0;
1814 }
1815
1816 /*
1817  * Unshare the filesystem structure if it is being shared
1818  */
1819 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1820 {
1821         struct fs_struct *fs = current->fs;
1822
1823         if (!(unshare_flags & CLONE_FS) || !fs)
1824                 return 0;
1825
1826         /* don't need lock here; in the worst case we'll do useless copy */
1827         if (fs->users == 1)
1828                 return 0;
1829
1830         *new_fsp = copy_fs_struct(fs);
1831         if (!*new_fsp)
1832                 return -ENOMEM;
1833
1834         return 0;
1835 }
1836
1837 /*
1838  * Unshare file descriptor table if it is being shared
1839  */
1840 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1841 {
1842         struct files_struct *fd = current->files;
1843         int error = 0;
1844
1845         if ((unshare_flags & CLONE_FILES) &&
1846             (fd && atomic_read(&fd->count) > 1)) {
1847                 *new_fdp = dup_fd(fd, &error);
1848                 if (!*new_fdp)
1849                         return error;
1850         }
1851
1852         return 0;
1853 }
1854
1855 /*
1856  * unshare allows a process to 'unshare' part of the process
1857  * context which was originally shared using clone.  copy_*
1858  * functions used by do_fork() cannot be used here directly
1859  * because they modify an inactive task_struct that is being
1860  * constructed. Here we are modifying the current, active,
1861  * task_struct.
1862  */
1863 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1864 {
1865         struct fs_struct *fs, *new_fs = NULL;
1866         struct files_struct *fd, *new_fd = NULL;
1867         struct cred *new_cred = NULL;
1868         struct nsproxy *new_nsproxy = NULL;
1869         int do_sysvsem = 0;
1870         int err;
1871
1872         /*
1873          * If unsharing a user namespace must also unshare the thread.
1874          */
1875         if (unshare_flags & CLONE_NEWUSER)
1876                 unshare_flags |= CLONE_THREAD | CLONE_FS;
1877         /*
1878          * If unsharing a thread from a thread group, must also unshare vm.
1879          */
1880         if (unshare_flags & CLONE_THREAD)
1881                 unshare_flags |= CLONE_VM;
1882         /*
1883          * If unsharing vm, must also unshare signal handlers.
1884          */
1885         if (unshare_flags & CLONE_VM)
1886                 unshare_flags |= CLONE_SIGHAND;
1887         /*
1888          * If unsharing namespace, must also unshare filesystem information.
1889          */
1890         if (unshare_flags & CLONE_NEWNS)
1891                 unshare_flags |= CLONE_FS;
1892
1893         err = check_unshare_flags(unshare_flags);
1894         if (err)
1895                 goto bad_unshare_out;
1896         /*
1897          * CLONE_NEWIPC must also detach from the undolist: after switching
1898          * to a new ipc namespace, the semaphore arrays from the old
1899          * namespace are unreachable.
1900          */
1901         if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1902                 do_sysvsem = 1;
1903         err = unshare_fs(unshare_flags, &new_fs);
1904         if (err)
1905                 goto bad_unshare_out;
1906         err = unshare_fd(unshare_flags, &new_fd);
1907         if (err)
1908                 goto bad_unshare_cleanup_fs;
1909         err = unshare_userns(unshare_flags, &new_cred);
1910         if (err)
1911                 goto bad_unshare_cleanup_fd;
1912         err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
1913                                          new_cred, new_fs);
1914         if (err)
1915                 goto bad_unshare_cleanup_cred;
1916
1917         if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
1918                 if (do_sysvsem) {
1919                         /*
1920                          * CLONE_SYSVSEM is equivalent to sys_exit().
1921                          */
1922                         exit_sem(current);
1923                 }
1924                 if (unshare_flags & CLONE_NEWIPC) {
1925                         /* Orphan segments in old ns (see sem above). */
1926                         exit_shm(current);
1927                         shm_init_task(current);
1928                 }
1929
1930                 if (new_nsproxy)
1931                         switch_task_namespaces(current, new_nsproxy);
1932
1933                 task_lock(current);
1934
1935                 if (new_fs) {
1936                         fs = current->fs;
1937                         spin_lock(&fs->lock);
1938                         current->fs = new_fs;
1939                         if (--fs->users)
1940                                 new_fs = NULL;
1941                         else
1942                                 new_fs = fs;
1943                         spin_unlock(&fs->lock);
1944                 }
1945
1946                 if (new_fd) {
1947                         fd = current->files;
1948                         current->files = new_fd;
1949                         new_fd = fd;
1950                 }
1951
1952                 task_unlock(current);
1953
1954                 if (new_cred) {
1955                         /* Install the new user namespace */
1956                         commit_creds(new_cred);
1957                         new_cred = NULL;
1958                 }
1959         }
1960
1961 bad_unshare_cleanup_cred:
1962         if (new_cred)
1963                 put_cred(new_cred);
1964 bad_unshare_cleanup_fd:
1965         if (new_fd)
1966                 put_files_struct(new_fd);
1967
1968 bad_unshare_cleanup_fs:
1969         if (new_fs)
1970                 free_fs_struct(new_fs);
1971
1972 bad_unshare_out:
1973         return err;
1974 }
1975
1976 /*
1977  *      Helper to unshare the files of the current task.
1978  *      We don't want to expose copy_files internals to
1979  *      the exec layer of the kernel.
1980  */
1981
1982 int unshare_files(struct files_struct **displaced)
1983 {
1984         struct task_struct *task = current;
1985         struct files_struct *copy = NULL;
1986         int error;
1987
1988         error = unshare_fd(CLONE_FILES, &copy);
1989         if (error || !copy) {
1990                 *displaced = NULL;
1991                 return error;
1992         }
1993         *displaced = task->files;
1994         task_lock(task);
1995         task->files = copy;
1996         task_unlock(task);
1997         return 0;
1998 }