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                         i_mmap_lock_write(mapping);
 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                         vma_interval_tree_insert_after(tmp, mpnt,
 442                                         &mapping->i_mmap);
 443                         flush_dcache_mmap_unlock(mapping);
 444                         i_mmap_unlock_write(mapping);
 445                 }
 446
 447                 /*
 448                  * Clear hugetlb-related page reserves for children. This only
 449                  * affects MAP_PRIVATE mappings. Faults generated by the child
 450                  * are not guaranteed to succeed, even if read-only
 451                  */
 452                 if (is_vm_hugetlb_page(tmp))
 453                         reset_vma_resv_huge_pages(tmp);
 454
 455                 /*
 456                  * Link in the new vma and copy the page table entries.
 457                  */
 458                 *pprev = tmp;
 459                 pprev = &tmp->vm_next;
 460                 tmp->vm_prev = prev;
 461                 prev = tmp;
 462
 463                 __vma_link_rb(mm, tmp, rb_link, rb_parent);
 464                 rb_link = &tmp->vm_rb.rb_right;
 465                 rb_parent = &tmp->vm_rb;
 466
 467                 mm->map_count++;
 468                 retval = copy_page_range(mm, oldmm, mpnt);
 469
 470                 if (tmp->vm_ops && tmp->vm_ops->open)
 471                         tmp->vm_ops->open(tmp);
 472
 473                 if (retval)
 474                         goto out;
 475         }
 476         /* a new mm has just been created */
 477         arch_dup_mmap(oldmm, mm);
 478         retval = 0;
 479 out:
 480         up_write(&mm->mmap_sem);
 481         flush_tlb_mm(oldmm);
 482         up_write(&oldmm->mmap_sem);
 483         uprobe_end_dup_mmap();
 484         return retval;
 485 fail_nomem_anon_vma_fork:
 486         mpol_put(vma_policy(tmp));
 487 fail_nomem_policy:
 488         kmem_cache_free(vm_area_cachep, tmp);
 489 fail_nomem:
 490         retval = -ENOMEM;
 491         vm_unacct_memory(charge);
 492         goto out;
 493 }
 494
 495 static inline int mm_alloc_pgd(struct mm_struct *mm)
 496 {
 497         mm->pgd = pgd_alloc(mm);
 498         if (unlikely(!mm->pgd))
 499                 return -ENOMEM;
 500         return 0;
 501 }
 502
 503 static inline void mm_free_pgd(struct mm_struct *mm)
 504 {
 505         pgd_free(mm, mm->pgd);
 506 }
 507 #else
 508 #define dup_mmap(mm, oldmm)     (0)
 509 #define mm_alloc_pgd(mm)        (0)
 510 #define mm_free_pgd(mm)
 511 #endif /* CONFIG_MMU */
 512
 513 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
 514
 515 #define allocate_mm()   (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
 516 #define free_mm(mm)     (kmem_cache_free(mm_cachep, (mm)))
 517
 518 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
 519
 520 static int __init coredump_filter_setup(char *s)
 521 {
 522         default_dump_filter =
 523                 (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
 524                 MMF_DUMP_FILTER_MASK;
 525         return 1;
 526 }
 527
 528 __setup("coredump_filter=", coredump_filter_setup);
 529
 530 #include <linux/init_task.h>
 531
 532 static void mm_init_aio(struct mm_struct *mm)
 533 {
 534 #ifdef CONFIG_AIO
 535         spin_lock_init(&mm->ioctx_lock);
 536         mm->ioctx_table = NULL;
 537 #endif
 538 }
 539
 540 static void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
 541 {
 542 #ifdef CONFIG_MEMCG
 543         mm->owner = p;
 544 #endif
 545 }
 546
 547 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
 548 {
 549         mm->mmap = NULL;
 550         mm->mm_rb = RB_ROOT;
 551         mm->vmacache_seqnum = 0;
 552         atomic_set(&mm->mm_users, 1);
 553         atomic_set(&mm->mm_count, 1);
 554         init_rwsem(&mm->mmap_sem);
 555         INIT_LIST_HEAD(&mm->mmlist);
 556         mm->core_state = NULL;
 557         atomic_long_set(&mm->nr_ptes, 0);
 558         mm->map_count = 0;
 559         mm->locked_vm = 0;
 560         mm->pinned_vm = 0;
 561         memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
 562         spin_lock_init(&mm->page_table_lock);
 563         mm_init_cpumask(mm);
 564         mm_init_aio(mm);
 565         mm_init_owner(mm, p);
 566         mmu_notifier_mm_init(mm);
 567         clear_tlb_flush_pending(mm);
 568 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
 569         mm->pmd_huge_pte = NULL;
 570 #endif
 571
 572         if (current->mm) {
 573                 mm->flags = current->mm->flags & MMF_INIT_MASK;
 574                 mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
 575         } else {
 576                 mm->flags = default_dump_filter;
 577                 mm->def_flags = 0;
 578         }
 579
 580         if (mm_alloc_pgd(mm))
 581                 goto fail_nopgd;
 582
 583         if (init_new_context(p, mm))
 584                 goto fail_nocontext;
 585
 586         return mm;
 587
 588 fail_nocontext:
 589         mm_free_pgd(mm);
 590 fail_nopgd:
 591         free_mm(mm);
 592         return NULL;
 593 }
 594
 595 static void check_mm(struct mm_struct *mm)
 596 {
 597         int i;
 598
 599         for (i = 0; i < NR_MM_COUNTERS; i++) {
 600                 long x = atomic_long_read(&mm->rss_stat.count[i]);
 601
 602                 if (unlikely(x))
 603                         printk(KERN_ALERT "BUG: Bad rss-counter state "
 604                                           "mm:%p idx:%d val:%ld\n", mm, i, x);
 605         }
 606 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
 607         VM_BUG_ON_MM(mm->pmd_huge_pte, mm);
 608 #endif
 609 }
 610
 611 /*
 612  * Allocate and initialize an mm_struct.
 613  */
 614 struct mm_struct *mm_alloc(void)
 615 {
 616         struct mm_struct *mm;
 617
 618         mm = allocate_mm();
 619         if (!mm)
 620                 return NULL;
 621
 622         memset(mm, 0, sizeof(*mm));
 623         return mm_init(mm, current);
 624 }
 625
 626 /*
 627  * Called when the last reference to the mm
 628  * is dropped: either by a lazy thread or by
 629  * mmput. Free the page directory and the mm.
 630  */
 631 void __mmdrop(struct mm_struct *mm)
 632 {
 633         BUG_ON(mm == &init_mm);
 634         mm_free_pgd(mm);
 635         destroy_context(mm);
 636         mmu_notifier_mm_destroy(mm);
 637         check_mm(mm);
 638         free_mm(mm);
 639 }
 640 EXPORT_SYMBOL_GPL(__mmdrop);
 641
 642 /*
 643  * Decrement the use count and release all resources for an mm.
 644  */
 645 void mmput(struct mm_struct *mm)
 646 {
 647         might_sleep();
 648
 649         if (atomic_dec_and_test(&mm->mm_users)) {
 650                 uprobe_clear_state(mm);
 651                 exit_aio(mm);
 652                 ksm_exit(mm);
 653                 khugepaged_exit(mm); /* must run before exit_mmap */
 654                 exit_mmap(mm);
 655                 set_mm_exe_file(mm, NULL);
 656                 if (!list_empty(&mm->mmlist)) {
 657                         spin_lock(&mmlist_lock);
 658                         list_del(&mm->mmlist);
 659                         spin_unlock(&mmlist_lock);
 660                 }
 661                 if (mm->binfmt)
 662                         module_put(mm->binfmt->module);
 663                 mmdrop(mm);
 664         }
 665 }
 666 EXPORT_SYMBOL_GPL(mmput);
 667
 668 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
 669 {
 670         if (new_exe_file)
 671                 get_file(new_exe_file);
 672         if (mm->exe_file)
 673                 fput(mm->exe_file);
 674         mm->exe_file = new_exe_file;
 675 }
 676
 677 struct file *get_mm_exe_file(struct mm_struct *mm)
 678 {
 679         struct file *exe_file;
 680
 681         /* We need mmap_sem to protect against races with removal of exe_file */
 682         down_read(&mm->mmap_sem);
 683         exe_file = mm->exe_file;
 684         if (exe_file)
 685                 get_file(exe_file);
 686         up_read(&mm->mmap_sem);
 687         return exe_file;
 688 }
 689
 690 static void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
 691 {
 692         /* It's safe to write the exe_file pointer without exe_file_lock because
 693          * this is called during fork when the task is not yet in /proc */
 694         newmm->exe_file = get_mm_exe_file(oldmm);
 695 }
 696
 697 /**
 698  * get_task_mm - acquire a reference to the task's mm
 699  *
 700  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
 701  * this kernel workthread has transiently adopted a user mm with use_mm,
 702  * to do its AIO) is not set and if so returns a reference to it, after
 703  * bumping up the use count.  User must release the mm via mmput()
 704  * after use.  Typically used by /proc and ptrace.
 705  */
 706 struct mm_struct *get_task_mm(struct task_struct *task)
 707 {
 708         struct mm_struct *mm;
 709
 710         task_lock(task);
 711         mm = task->mm;
 712         if (mm) {
 713                 if (task->flags & PF_KTHREAD)
 714                         mm = NULL;
 715                 else
 716                         atomic_inc(&mm->mm_users);
 717         }
 718         task_unlock(task);
 719         return mm;
 720 }
 721 EXPORT_SYMBOL_GPL(get_task_mm);
 722
 723 struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
 724 {
 725         struct mm_struct *mm;
 726         int err;
 727
 728         err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
 729         if (err)
 730                 return ERR_PTR(err);
 731
 732         mm = get_task_mm(task);
 733         if (mm && mm != current->mm &&
 734                         !ptrace_may_access(task, mode)) {
 735                 mmput(mm);
 736                 mm = ERR_PTR(-EACCES);
 737         }
 738         mutex_unlock(&task->signal->cred_guard_mutex);
 739
 740         return mm;
 741 }
 742
 743 static void complete_vfork_done(struct task_struct *tsk)
 744 {
 745         struct completion *vfork;
 746
 747         task_lock(tsk);
 748         vfork = tsk->vfork_done;
 749         if (likely(vfork)) {
 750                 tsk->vfork_done = NULL;
 751                 complete(vfork);
 752         }
 753         task_unlock(tsk);
 754 }
 755
 756 static int wait_for_vfork_done(struct task_struct *child,
 757                                 struct completion *vfork)
 758 {
 759         int killed;
 760
 761         freezer_do_not_count();
 762         killed = wait_for_completion_killable(vfork);
 763         freezer_count();
 764
 765         if (killed) {
 766                 task_lock(child);
 767                 child->vfork_done = NULL;
 768                 task_unlock(child);
 769         }
 770
 771         put_task_struct(child);
 772         return killed;
 773 }
 774
 775 /* Please note the differences between mmput and mm_release.
 776  * mmput is called whenever we stop holding onto a mm_struct,
 777  * error success whatever.
 778  *
 779  * mm_release is called after a mm_struct has been removed
 780  * from the current process.
 781  *
 782  * This difference is important for error handling, when we
 783  * only half set up a mm_struct for a new process and need to restore
 784  * the old one.  Because we mmput the new mm_struct before
 785  * restoring the old one. . .
 786  * Eric Biederman 10 January 1998
 787  */
 788 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
 789 {
 790         /* Get rid of any futexes when releasing the mm */
 791 #ifdef CONFIG_FUTEX
 792         if (unlikely(tsk->robust_list)) {
 793                 exit_robust_list(tsk);
 794                 tsk->robust_list = NULL;
 795         }
 796 #ifdef CONFIG_COMPAT
 797         if (unlikely(tsk->compat_robust_list)) {
 798                 compat_exit_robust_list(tsk);
 799                 tsk->compat_robust_list = NULL;
 800         }
 801 #endif
 802         if (unlikely(!list_empty(&tsk->pi_state_list)))
 803                 exit_pi_state_list(tsk);
 804 #endif
 805
 806         uprobe_free_utask(tsk);
 807
 808         /* Get rid of any cached register state */
 809         deactivate_mm(tsk, mm);
 810
 811         /*
 812          * If we're exiting normally, clear a user-space tid field if
 813          * requested.  We leave this alone when dying by signal, to leave
 814          * the value intact in a core dump, and to save the unnecessary
 815          * trouble, say, a killed vfork parent shouldn't touch this mm.
 816          * Userland only wants this done for a sys_exit.
 817          */
 818         if (tsk->clear_child_tid) {
 819                 if (!(tsk->flags & PF_SIGNALED) &&
 820                     atomic_read(&mm->mm_users) > 1) {
 821                         /*
 822                          * We don't check the error code - if userspace has
 823                          * not set up a proper pointer then tough luck.
 824                          */
 825                         put_user(0, tsk->clear_child_tid);
 826                         sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
 827                                         1, NULL, NULL, 0);
 828                 }
 829                 tsk->clear_child_tid = NULL;
 830         }
 831
 832         /*
 833          * All done, finally we can wake up parent and return this mm to him.
 834          * Also kthread_stop() uses this completion for synchronization.
 835          */
 836         if (tsk->vfork_done)
 837                 complete_vfork_done(tsk);
 838 }
 839
 840 /*
 841  * Allocate a new mm structure and copy contents from the
 842  * mm structure of the passed in task structure.
 843  */
 844 static struct mm_struct *dup_mm(struct task_struct *tsk)
 845 {
 846         struct mm_struct *mm, *oldmm = current->mm;
 847         int err;
 848
 849         mm = allocate_mm();
 850         if (!mm)
 851                 goto fail_nomem;
 852
 853         memcpy(mm, oldmm, sizeof(*mm));
 854
 855         if (!mm_init(mm, tsk))
 856                 goto fail_nomem;
 857
 858         dup_mm_exe_file(oldmm, mm);
 859
 860         err = dup_mmap(mm, oldmm);
 861         if (err)
 862                 goto free_pt;
 863
 864         mm->hiwater_rss = get_mm_rss(mm);
 865         mm->hiwater_vm = mm->total_vm;
 866
 867         if (mm->binfmt && !try_module_get(mm->binfmt->module))
 868                 goto free_pt;
 869
 870         return mm;
 871
 872 free_pt:
 873         /* don't put binfmt in mmput, we haven't got module yet */
 874         mm->binfmt = NULL;
 875         mmput(mm);
 876
 877 fail_nomem:
 878         return NULL;
 879 }
 880
 881 static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
 882 {
 883         struct mm_struct *mm, *oldmm;
 884         int retval;
 885
 886         tsk->min_flt = tsk->maj_flt = 0;
 887         tsk->nvcsw = tsk->nivcsw = 0;
 888 #ifdef CONFIG_DETECT_HUNG_TASK
 889         tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
 890 #endif
 891
 892         tsk->mm = NULL;
 893         tsk->active_mm = NULL;
 894
 895         /*
 896          * Are we cloning a kernel thread?
 897          *
 898          * We need to steal a active VM for that..
 899          */
 900         oldmm = current->mm;
 901         if (!oldmm)
 902                 return 0;
 903
 904         /* initialize the new vmacache entries */
 905         vmacache_flush(tsk);
 906
 907         if (clone_flags & CLONE_VM) {
 908                 atomic_inc(&oldmm->mm_users);
 909                 mm = oldmm;
 910                 goto good_mm;
 911         }
 912
 913         retval = -ENOMEM;
 914         mm = dup_mm(tsk);
 915         if (!mm)
 916                 goto fail_nomem;
 917
 918 good_mm:
 919         tsk->mm = mm;
 920         tsk->active_mm = mm;
 921         return 0;
 922
 923 fail_nomem:
 924         return retval;
 925 }
 926
 927 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
 928 {
 929         struct fs_struct *fs = current->fs;
 930         if (clone_flags & CLONE_FS) {
 931                 /* tsk->fs is already what we want */
 932                 spin_lock(&fs->lock);
 933                 if (fs->in_exec) {
 934                         spin_unlock(&fs->lock);
 935                         return -EAGAIN;
 936                 }
 937                 fs->users++;
 938                 spin_unlock(&fs->lock);
 939                 return 0;
 940         }
 941         tsk->fs = copy_fs_struct(fs);
 942         if (!tsk->fs)
 943                 return -ENOMEM;
 944         return 0;
 945 }
 946
 947 static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
 948 {
 949         struct files_struct *oldf, *newf;
 950         int error = 0;
 951
 952         /*
 953          * A background process may not have any files ...
 954          */
 955         oldf = current->files;
 956         if (!oldf)
 957                 goto out;
 958
 959         if (clone_flags & CLONE_FILES) {
 960                 atomic_inc(&oldf->count);
 961                 goto out;
 962         }
 963
 964         newf = dup_fd(oldf, &error);
 965         if (!newf)
 966                 goto out;
 967
 968         tsk->files = newf;
 969         error = 0;
 970 out:
 971         return error;
 972 }
 973
 974 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
 975 {
 976 #ifdef CONFIG_BLOCK
 977         struct io_context *ioc = current->io_context;
 978         struct io_context *new_ioc;
 979
 980         if (!ioc)
 981                 return 0;
 982         /*
 983          * Share io context with parent, if CLONE_IO is set
 984          */
 985         if (clone_flags & CLONE_IO) {
 986                 ioc_task_link(ioc);
 987                 tsk->io_context = ioc;
 988         } else if (ioprio_valid(ioc->ioprio)) {
 989                 new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
 990                 if (unlikely(!new_ioc))
 991                         return -ENOMEM;
 992
 993                 new_ioc->ioprio = ioc->ioprio;
 994                 put_io_context(new_ioc);
 995         }
 996 #endif
 997         return 0;
 998 }
 999
1000 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
1001 {
1002         struct sighand_struct *sig;
1003
1004         if (clone_flags & CLONE_SIGHAND) {
1005                 atomic_inc(&current->sighand->count);
1006                 return 0;
1007         }
1008         sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
1009         rcu_assign_pointer(tsk->sighand, sig);
1010         if (!sig)
1011                 return -ENOMEM;
1012         atomic_set(&sig->count, 1);
1013         memcpy(sig->action, current->sighand->action, sizeof(sig->action));
1014         return 0;
1015 }
1016
1017 void __cleanup_sighand(struct sighand_struct *sighand)
1018 {
1019         if (atomic_dec_and_test(&sighand->count)) {
1020                 signalfd_cleanup(sighand);
1021                 /*
1022                  * sighand_cachep is SLAB_DESTROY_BY_RCU so we can free it
1023                  * without an RCU grace period, see __lock_task_sighand().
1024                  */
1025                 kmem_cache_free(sighand_cachep, sighand);
1026         }
1027 }
1028
1029 /*
1030  * Initialize POSIX timer handling for a thread group.
1031  */
1032 static void posix_cpu_timers_init_group(struct signal_struct *sig)
1033 {
1034         unsigned long cpu_limit;
1035
1036         /* Thread group counters. */
1037         thread_group_cputime_init(sig);
1038
1039         cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1040         if (cpu_limit != RLIM_INFINITY) {
1041                 sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
1042                 sig->cputimer.running = 1;
1043         }
1044
1045         /* The timer lists. */
1046         INIT_LIST_HEAD(&sig->cpu_timers[0]);
1047         INIT_LIST_HEAD(&sig->cpu_timers[1]);
1048         INIT_LIST_HEAD(&sig->cpu_timers[2]);
1049 }
1050
1051 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1052 {
1053         struct signal_struct *sig;
1054
1055         if (clone_flags & CLONE_THREAD)
1056                 return 0;
1057
1058         sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1059         tsk->signal = sig;
1060         if (!sig)
1061                 return -ENOMEM;
1062
1063         sig->nr_threads = 1;
1064         atomic_set(&sig->live, 1);
1065         atomic_set(&sig->sigcnt, 1);
1066
1067         /* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */
1068         sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node);
1069         tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);
1070
1071         init_waitqueue_head(&sig->wait_chldexit);
1072         sig->curr_target = tsk;
1073         init_sigpending(&sig->shared_pending);
1074         INIT_LIST_HEAD(&sig->posix_timers);
1075         seqlock_init(&sig->stats_lock);
1076
1077         hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1078         sig->real_timer.function = it_real_fn;
1079
1080         task_lock(current->group_leader);
1081         memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1082         task_unlock(current->group_leader);
1083
1084         posix_cpu_timers_init_group(sig);
1085
1086         tty_audit_fork(sig);
1087         sched_autogroup_fork(sig);
1088
1089 #ifdef CONFIG_CGROUPS
1090         init_rwsem(&sig->group_rwsem);
1091 #endif
1092
1093         sig->oom_score_adj = current->signal->oom_score_adj;
1094         sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1095
1096         sig->has_child_subreaper = current->signal->has_child_subreaper ||
1097                                    current->signal->is_child_subreaper;
1098
1099         mutex_init(&sig->cred_guard_mutex);
1100
1101         return 0;
1102 }
1103
1104 static void copy_seccomp(struct task_struct *p)
1105 {
1106 #ifdef CONFIG_SECCOMP
1107         /*
1108          * Must be called with sighand->lock held, which is common to
1109          * all threads in the group. Holding cred_guard_mutex is not
1110          * needed because this new task is not yet running and cannot
1111          * be racing exec.
1112          */
1113         assert_spin_locked(&current->sighand->siglock);
1114
1115         /* Ref-count the new filter user, and assign it. */
1116         get_seccomp_filter(current);
1117         p->seccomp = current->seccomp;
1118
1119         /*
1120          * Explicitly enable no_new_privs here in case it got set
1121          * between the task_struct being duplicated and holding the
1122          * sighand lock. The seccomp state and nnp must be in sync.
1123          */
1124         if (task_no_new_privs(current))
1125                 task_set_no_new_privs(p);
1126
1127         /*
1128          * If the parent gained a seccomp mode after copying thread
1129          * flags and between before we held the sighand lock, we have
1130          * to manually enable the seccomp thread flag here.
1131          */
1132         if (p->seccomp.mode != SECCOMP_MODE_DISABLED)
1133                 set_tsk_thread_flag(p, TIF_SECCOMP);
1134 #endif
1135 }
1136
1137 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1138 {
1139         current->clear_child_tid = tidptr;
1140
1141         return task_pid_vnr(current);
1142 }
1143
1144 static void rt_mutex_init_task(struct task_struct *p)
1145 {
1146         raw_spin_lock_init(&p->pi_lock);
1147 #ifdef CONFIG_RT_MUTEXES
1148         p->pi_waiters = RB_ROOT;
1149         p->pi_waiters_leftmost = NULL;
1150         p->pi_blocked_on = NULL;
1151 #endif
1152 }
1153
1154 /*
1155  * Initialize POSIX timer handling for a single task.
1156  */
1157 static void posix_cpu_timers_init(struct task_struct *tsk)
1158 {
1159         tsk->cputime_expires.prof_exp = 0;
1160         tsk->cputime_expires.virt_exp = 0;
1161         tsk->cputime_expires.sched_exp = 0;
1162         INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1163         INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1164         INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1165 }
1166
1167 static inline void
1168 init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
1169 {
1170          task->pids[type].pid = pid;
1171 }
1172
1173 /*
1174  * This creates a new process as a copy of the old one,
1175  * but does not actually start it yet.
1176  *
1177  * It copies the registers, and all the appropriate
1178  * parts of the process environment (as per the clone
1179  * flags). The actual kick-off is left to the caller.
1180  */
1181 static struct task_struct *copy_process(unsigned long clone_flags,
1182                                         unsigned long stack_start,
1183                                         unsigned long stack_size,
1184                                         int __user *child_tidptr,
1185                                         struct pid *pid,
1186                                         int trace)
1187 {
1188         int retval;
1189         struct task_struct *p;
1190
1191         if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1192                 return ERR_PTR(-EINVAL);
1193
1194         if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
1195                 return ERR_PTR(-EINVAL);
1196
1197         /*
1198          * Thread groups must share signals as well, and detached threads
1199          * can only be started up within the thread group.
1200          */
1201         if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1202                 return ERR_PTR(-EINVAL);
1203
1204         /*
1205          * Shared signal handlers imply shared VM. By way of the above,
1206          * thread groups also imply shared VM. Blocking this case allows
1207          * for various simplifications in other code.
1208          */
1209         if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1210                 return ERR_PTR(-EINVAL);
1211
1212         /*
1213          * Siblings of global init remain as zombies on exit since they are
1214          * not reaped by their parent (swapper). To solve this and to avoid
1215          * multi-rooted process trees, prevent global and container-inits
1216          * from creating siblings.
1217          */
1218         if ((clone_flags & CLONE_PARENT) &&
1219                                 current->signal->flags & SIGNAL_UNKILLABLE)
1220                 return ERR_PTR(-EINVAL);
1221
1222         /*
1223          * If the new process will be in a different pid or user namespace
1224          * do not allow it to share a thread group or signal handlers or
1225          * parent with the forking task.
1226          */
1227         if (clone_flags & CLONE_SIGHAND) {
1228                 if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
1229                     (task_active_pid_ns(current) !=
1230                                 current->nsproxy->pid_ns_for_children))
1231                         return ERR_PTR(-EINVAL);
1232         }
1233
1234         retval = security_task_create(clone_flags);
1235         if (retval)
1236                 goto fork_out;
1237
1238         retval = -ENOMEM;
1239         p = dup_task_struct(current);
1240         if (!p)
1241                 goto fork_out;
1242
1243         ftrace_graph_init_task(p);
1244
1245         rt_mutex_init_task(p);
1246
1247 #ifdef CONFIG_PROVE_LOCKING
1248         DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1249         DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1250 #endif
1251         retval = -EAGAIN;
1252         if (atomic_read(&p->real_cred->user->processes) >=
1253                         task_rlimit(p, RLIMIT_NPROC)) {
1254                 if (p->real_cred->user != INIT_USER &&
1255                     !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
1256                         goto bad_fork_free;
1257         }
1258         current->flags &= ~PF_NPROC_EXCEEDED;
1259
1260         retval = copy_creds(p, clone_flags);
1261         if (retval < 0)
1262                 goto bad_fork_free;
1263
1264         /*
1265          * If multiple threads are within copy_process(), then this check
1266          * triggers too late. This doesn't hurt, the check is only there
1267          * to stop root fork bombs.
1268          */
1269         retval = -EAGAIN;
1270         if (nr_threads >= max_threads)
1271                 goto bad_fork_cleanup_count;
1272
1273         if (!try_module_get(task_thread_info(p)->exec_domain->module))
1274                 goto bad_fork_cleanup_count;
1275
1276         delayacct_tsk_init(p);  /* Must remain after dup_task_struct() */
1277         p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
1278         p->flags |= PF_FORKNOEXEC;
1279         INIT_LIST_HEAD(&p->children);
1280         INIT_LIST_HEAD(&p->sibling);
1281         rcu_copy_process(p);
1282         p->vfork_done = NULL;
1283         spin_lock_init(&p->alloc_lock);
1284
1285         init_sigpending(&p->pending);
1286
1287         p->utime = p->stime = p->gtime = 0;
1288         p->utimescaled = p->stimescaled = 0;
1289 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
1290         p->prev_cputime.utime = p->prev_cputime.stime = 0;
1291 #endif
1292 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
1293         seqlock_init(&p->vtime_seqlock);
1294         p->vtime_snap = 0;
1295         p->vtime_snap_whence = VTIME_SLEEPING;
1296 #endif
1297
1298 #if defined(SPLIT_RSS_COUNTING)
1299         memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1300 #endif
1301
1302         p->default_timer_slack_ns = current->timer_slack_ns;
1303
1304         task_io_accounting_init(&p->ioac);
1305         acct_clear_integrals(p);
1306
1307         posix_cpu_timers_init(p);
1308
1309         p->start_time = ktime_get_ns();
1310         p->real_start_time = ktime_get_boot_ns();
1311         p->io_context = NULL;
1312         p->audit_context = NULL;
1313         if (clone_flags & CLONE_THREAD)
1314                 threadgroup_change_begin(current);
1315         cgroup_fork(p);
1316 #ifdef CONFIG_NUMA
1317         p->mempolicy = mpol_dup(p->mempolicy);
1318         if (IS_ERR(p->mempolicy)) {
1319                 retval = PTR_ERR(p->mempolicy);
1320                 p->mempolicy = NULL;
1321                 goto bad_fork_cleanup_threadgroup_lock;
1322         }
1323 #endif
1324 #ifdef CONFIG_CPUSETS
1325         p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
1326         p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
1327         seqcount_init(&p->mems_allowed_seq);
1328 #endif
1329 #ifdef CONFIG_TRACE_IRQFLAGS
1330         p->irq_events = 0;
1331         p->hardirqs_enabled = 0;
1332         p->hardirq_enable_ip = 0;
1333         p->hardirq_enable_event = 0;
1334         p->hardirq_disable_ip = _THIS_IP_;
1335         p->hardirq_disable_event = 0;
1336         p->softirqs_enabled = 1;
1337         p->softirq_enable_ip = _THIS_IP_;
1338         p->softirq_enable_event = 0;
1339         p->softirq_disable_ip = 0;
1340         p->softirq_disable_event = 0;
1341         p->hardirq_context = 0;
1342         p->softirq_context = 0;
1343 #endif
1344 #ifdef CONFIG_LOCKDEP
1345         p->lockdep_depth = 0; /* no locks held yet */
1346         p->curr_chain_key = 0;
1347         p->lockdep_recursion = 0;
1348 #endif
1349
1350 #ifdef CONFIG_DEBUG_MUTEXES
1351         p->blocked_on = NULL; /* not blocked yet */
1352 #endif
1353 #ifdef CONFIG_BCACHE
1354         p->sequential_io        = 0;
1355         p->sequential_io_avg    = 0;
1356 #endif
1357
1358         /* Perform scheduler related setup. Assign this task to a CPU. */
1359         retval = sched_fork(clone_flags, p);
1360         if (retval)
1361                 goto bad_fork_cleanup_policy;
1362
1363         retval = perf_event_init_task(p);
1364         if (retval)
1365                 goto bad_fork_cleanup_policy;
1366         retval = audit_alloc(p);
1367         if (retval)
1368                 goto bad_fork_cleanup_perf;
1369         /* copy all the process information */
1370         shm_init_task(p);
1371         retval = copy_semundo(clone_flags, p);
1372         if (retval)
1373                 goto bad_fork_cleanup_audit;
1374         retval = copy_files(clone_flags, p);
1375         if (retval)
1376                 goto bad_fork_cleanup_semundo;
1377         retval = copy_fs(clone_flags, p);
1378         if (retval)
1379                 goto bad_fork_cleanup_files;
1380         retval = copy_sighand(clone_flags, p);
1381         if (retval)
1382                 goto bad_fork_cleanup_fs;
1383         retval = copy_signal(clone_flags, p);
1384         if (retval)
1385                 goto bad_fork_cleanup_sighand;
1386         retval = copy_mm(clone_flags, p);
1387         if (retval)
1388                 goto bad_fork_cleanup_signal;
1389         retval = copy_namespaces(clone_flags, p);
1390         if (retval)
1391                 goto bad_fork_cleanup_mm;
1392         retval = copy_io(clone_flags, p);
1393         if (retval)
1394                 goto bad_fork_cleanup_namespaces;
1395         retval = copy_thread(clone_flags, stack_start, stack_size, p);
1396         if (retval)
1397                 goto bad_fork_cleanup_io;
1398
1399         if (pid != &init_struct_pid) {
1400                 retval = -ENOMEM;
1401                 pid = alloc_pid(p->nsproxy->pid_ns_for_children);
1402                 if (!pid)
1403                         goto bad_fork_cleanup_io;
1404         }
1405
1406         p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1407         /*
1408          * Clear TID on mm_release()?
1409          */
1410         p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
1411 #ifdef CONFIG_BLOCK
1412         p->plug = NULL;
1413 #endif
1414 #ifdef CONFIG_FUTEX
1415         p->robust_list = NULL;
1416 #ifdef CONFIG_COMPAT
1417         p->compat_robust_list = NULL;
1418 #endif
1419         INIT_LIST_HEAD(&p->pi_state_list);
1420         p->pi_state_cache = NULL;
1421 #endif
1422         /*
1423          * sigaltstack should be cleared when sharing the same VM
1424          */
1425         if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1426                 p->sas_ss_sp = p->sas_ss_size = 0;
1427
1428         /*
1429          * Syscall tracing and stepping should be turned off in the
1430          * child regardless of CLONE_PTRACE.
1431          */
1432         user_disable_single_step(p);
1433         clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1434 #ifdef TIF_SYSCALL_EMU
1435         clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1436 #endif
1437         clear_all_latency_tracing(p);
1438
1439         /* ok, now we should be set up.. */
1440         p->pid = pid_nr(pid);
1441         if (clone_flags & CLONE_THREAD) {
1442                 p->exit_signal = -1;
1443                 p->group_leader = current->group_leader;
1444                 p->tgid = current->tgid;
1445         } else {
1446                 if (clone_flags & CLONE_PARENT)
1447                         p->exit_signal = current->group_leader->exit_signal;
1448                 else
1449                         p->exit_signal = (clone_flags & CSIGNAL);
1450                 p->group_leader = p;
1451                 p->tgid = p->pid;
1452         }
1453
1454         p->nr_dirtied = 0;
1455         p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
1456         p->dirty_paused_when = 0;
1457
1458         p->pdeath_signal = 0;
1459         INIT_LIST_HEAD(&p->thread_group);
1460         p->task_works = NULL;
1461
1462         /*
1463          * Make it visible to the rest of the system, but dont wake it up yet.
1464          * Need tasklist lock for parent etc handling!
1465          */
1466         write_lock_irq(&tasklist_lock);
1467
1468         /* CLONE_PARENT re-uses the old parent */
1469         if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1470                 p->real_parent = current->real_parent;
1471                 p->parent_exec_id = current->parent_exec_id;
1472         } else {
1473                 p->real_parent = current;
1474                 p->parent_exec_id = current->self_exec_id;
1475         }
1476
1477         spin_lock(&current->sighand->siglock);
1478
1479         /*
1480          * Copy seccomp details explicitly here, in case they were changed
1481          * before holding sighand lock.
1482          */
1483         copy_seccomp(p);
1484
1485         /*
1486          * Process group and session signals need to be delivered to just the
1487          * parent before the fork or both the parent and the child after the
1488          * fork. Restart if a signal comes in before we add the new process to
1489          * it's process group.
1490          * A fatal signal pending means that current will exit, so the new
1491          * thread can't slip out of an OOM kill (or normal SIGKILL).
1492         */
1493         recalc_sigpending();
1494         if (signal_pending(current)) {
1495                 spin_unlock(&current->sighand->siglock);
1496                 write_unlock_irq(&tasklist_lock);
1497                 retval = -ERESTARTNOINTR;
1498                 goto bad_fork_free_pid;
1499         }
1500
1501         if (likely(p->pid)) {
1502                 ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
1503
1504                 init_task_pid(p, PIDTYPE_PID, pid);
1505                 if (thread_group_leader(p)) {
1506                         init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
1507                         init_task_pid(p, PIDTYPE_SID, task_session(current));
1508
1509                         if (is_child_reaper(pid)) {
1510                                 ns_of_pid(pid)->child_reaper = p;
1511                                 p->signal->flags |= SIGNAL_UNKILLABLE;
1512                         }
1513
1514                         p->signal->leader_pid = pid;
1515                         p->signal->tty = tty_kref_get(current->signal->tty);
1516                         list_add_tail(&p->sibling, &p->real_parent->children);
1517                         list_add_tail_rcu(&p->tasks, &init_task.tasks);
1518                         attach_pid(p, PIDTYPE_PGID);
1519                         attach_pid(p, PIDTYPE_SID);
1520                         __this_cpu_inc(process_counts);
1521                 } else {
1522                         current->signal->nr_threads++;
1523                         atomic_inc(&current->signal->live);
1524                         atomic_inc(&current->signal->sigcnt);
1525                         list_add_tail_rcu(&p->thread_group,
1526                                           &p->group_leader->thread_group);
1527                         list_add_tail_rcu(&p->thread_node,
1528                                           &p->signal->thread_head);
1529                 }
1530                 attach_pid(p, PIDTYPE_PID);
1531                 nr_threads++;
1532         }
1533
1534         total_forks++;
1535         spin_unlock(&current->sighand->siglock);
1536         syscall_tracepoint_update(p);
1537         write_unlock_irq(&tasklist_lock);
1538
1539         proc_fork_connector(p);
1540         cgroup_post_fork(p);
1541         if (clone_flags & CLONE_THREAD)
1542                 threadgroup_change_end(current);
1543         perf_event_fork(p);
1544
1545         trace_task_newtask(p, clone_flags);
1546         uprobe_copy_process(p, clone_flags);
1547
1548         return p;
1549
1550 bad_fork_free_pid:
1551         if (pid != &init_struct_pid)
1552                 free_pid(pid);
1553 bad_fork_cleanup_io:
1554         if (p->io_context)
1555                 exit_io_context(p);
1556 bad_fork_cleanup_namespaces:
1557         exit_task_namespaces(p);
1558 bad_fork_cleanup_mm:
1559         if (p->mm)
1560                 mmput(p->mm);
1561 bad_fork_cleanup_signal:
1562         if (!(clone_flags & CLONE_THREAD))
1563                 free_signal_struct(p->signal);
1564 bad_fork_cleanup_sighand:
1565         __cleanup_sighand(p->sighand);
1566 bad_fork_cleanup_fs:
1567         exit_fs(p); /* blocking */
1568 bad_fork_cleanup_files:
1569         exit_files(p); /* blocking */
1570 bad_fork_cleanup_semundo:
1571         exit_sem(p);
1572 bad_fork_cleanup_audit:
1573         audit_free(p);
1574 bad_fork_cleanup_perf:
1575         perf_event_free_task(p);
1576 bad_fork_cleanup_policy:
1577 #ifdef CONFIG_NUMA
1578         mpol_put(p->mempolicy);
1579 bad_fork_cleanup_threadgroup_lock:
1580 #endif
1581         if (clone_flags & CLONE_THREAD)
1582                 threadgroup_change_end(current);
1583         delayacct_tsk_free(p);
1584         module_put(task_thread_info(p)->exec_domain->module);
1585 bad_fork_cleanup_count:
1586         atomic_dec(&p->cred->user->processes);
1587         exit_creds(p);
1588 bad_fork_free:
1589         free_task(p);
1590 fork_out:
1591         return ERR_PTR(retval);
1592 }
1593
1594 static inline void init_idle_pids(struct pid_link *links)
1595 {
1596         enum pid_type type;
1597
1598         for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1599                 INIT_HLIST_NODE(&links[type].node); /* not really needed */
1600                 links[type].pid = &init_struct_pid;
1601         }
1602 }
1603
1604 struct task_struct *fork_idle(int cpu)
1605 {
1606         struct task_struct *task;
1607         task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0);
1608         if (!IS_ERR(task)) {
1609                 init_idle_pids(task->pids);
1610                 init_idle(task, cpu);
1611         }
1612
1613         return task;
1614 }
1615
1616 /*
1617  *  Ok, this is the main fork-routine.
1618  *
1619  * It copies the process, and if successful kick-starts
1620  * it and waits for it to finish using the VM if required.
1621  */
1622 long do_fork(unsigned long clone_flags,
1623               unsigned long stack_start,
1624               unsigned long stack_size,
1625               int __user *parent_tidptr,
1626               int __user *child_tidptr)
1627 {
1628         struct task_struct *p;
1629         int trace = 0;
1630         long nr;
1631
1632         /*
1633          * Determine whether and which event to report to ptracer.  When
1634          * called from kernel_thread or CLONE_UNTRACED is explicitly
1635          * requested, no event is reported; otherwise, report if the event
1636          * for the type of forking is enabled.
1637          */
1638         if (!(clone_flags & CLONE_UNTRACED)) {
1639                 if (clone_flags & CLONE_VFORK)
1640                         trace = PTRACE_EVENT_VFORK;
1641                 else if ((clone_flags & CSIGNAL) != SIGCHLD)
1642                         trace = PTRACE_EVENT_CLONE;
1643                 else
1644                         trace = PTRACE_EVENT_FORK;
1645
1646                 if (likely(!ptrace_event_enabled(current, trace)))
1647                         trace = 0;
1648         }
1649
1650         p = copy_process(clone_flags, stack_start, stack_size,
1651                          child_tidptr, NULL, trace);
1652         /*
1653          * Do this prior waking up the new thread - the thread pointer
1654          * might get invalid after that point, if the thread exits quickly.
1655          */
1656         if (!IS_ERR(p)) {
1657                 struct completion vfork;
1658                 struct pid *pid;
1659
1660                 trace_sched_process_fork(current, p);
1661
1662                 pid = get_task_pid(p, PIDTYPE_PID);
1663                 nr = pid_vnr(pid);
1664
1665                 if (clone_flags & CLONE_PARENT_SETTID)
1666                         put_user(nr, parent_tidptr);
1667
1668                 if (clone_flags & CLONE_VFORK) {
1669                         p->vfork_done = &vfork;
1670                         init_completion(&vfork);
1671                         get_task_struct(p);
1672                 }
1673
1674                 wake_up_new_task(p);
1675
1676                 /* forking complete and child started to run, tell ptracer */
1677                 if (unlikely(trace))
1678                         ptrace_event_pid(trace, pid);
1679
1680                 if (clone_flags & CLONE_VFORK) {
1681                         if (!wait_for_vfork_done(p, &vfork))
1682                                 ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
1683                 }
1684
1685                 put_pid(pid);
1686         } else {
1687                 nr = PTR_ERR(p);
1688         }
1689         return nr;
1690 }
1691
1692 /*
1693  * Create a kernel thread.
1694  */
1695 pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
1696 {
1697         return do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
1698                 (unsigned long)arg, NULL, NULL);
1699 }
1700
1701 #ifdef __ARCH_WANT_SYS_FORK
1702 SYSCALL_DEFINE0(fork)
1703 {
1704 #ifdef CONFIG_MMU
1705         return do_fork(SIGCHLD, 0, 0, NULL, NULL);
1706 #else
1707         /* can not support in nommu mode */
1708         return -EINVAL;
1709 #endif
1710 }
1711 #endif
1712
1713 #ifdef __ARCH_WANT_SYS_VFORK
1714 SYSCALL_DEFINE0(vfork)
1715 {
1716         return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0,
1717                         0, NULL, NULL);
1718 }
1719 #endif
1720
1721 #ifdef __ARCH_WANT_SYS_CLONE
1722 #ifdef CONFIG_CLONE_BACKWARDS
1723 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1724                  int __user *, parent_tidptr,
1725                  int, tls_val,
1726                  int __user *, child_tidptr)
1727 #elif defined(CONFIG_CLONE_BACKWARDS2)
1728 SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
1729                  int __user *, parent_tidptr,
1730                  int __user *, child_tidptr,
1731                  int, tls_val)
1732 #elif defined(CONFIG_CLONE_BACKWARDS3)
1733 SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
1734                 int, stack_size,
1735                 int __user *, parent_tidptr,
1736                 int __user *, child_tidptr,
1737                 int, tls_val)
1738 #else
1739 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1740                  int __user *, parent_tidptr,
1741                  int __user *, child_tidptr,
1742                  int, tls_val)
1743 #endif
1744 {
1745         return do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr);
1746 }
1747 #endif
1748
1749 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1750 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1751 #endif
1752
1753 static void sighand_ctor(void *data)
1754 {
1755         struct sighand_struct *sighand = data;
1756
1757         spin_lock_init(&sighand->siglock);
1758         init_waitqueue_head(&sighand->signalfd_wqh);
1759 }
1760
1761 void __init proc_caches_init(void)
1762 {
1763         sighand_cachep = kmem_cache_create("sighand_cache",
1764                         sizeof(struct sighand_struct), 0,
1765                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1766                         SLAB_NOTRACK, sighand_ctor);
1767         signal_cachep = kmem_cache_create("signal_cache",
1768                         sizeof(struct signal_struct), 0,
1769                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1770         files_cachep = kmem_cache_create("files_cache",
1771                         sizeof(struct files_struct), 0,
1772                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1773         fs_cachep = kmem_cache_create("fs_cache",
1774                         sizeof(struct fs_struct), 0,
1775                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1776         /*
1777          * FIXME! The "sizeof(struct mm_struct)" currently includes the
1778          * whole struct cpumask for the OFFSTACK case. We could change
1779          * this to *only* allocate as much of it as required by the
1780          * maximum number of CPU's we can ever have.  The cpumask_allocation
1781          * is at the end of the structure, exactly for that reason.
1782          */
1783         mm_cachep = kmem_cache_create("mm_struct",
1784                         sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1785                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1786         vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1787         mmap_init();
1788         nsproxy_cache_init();
1789 }
1790
1791 /*
1792  * Check constraints on flags passed to the unshare system call.
1793  */
1794 static int check_unshare_flags(unsigned long unshare_flags)
1795 {
1796         if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1797                                 CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1798                                 CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
1799                                 CLONE_NEWUSER|CLONE_NEWPID))
1800                 return -EINVAL;
1801         /*
1802          * Not implemented, but pretend it works if there is nothing to
1803          * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
1804          * needs to unshare vm.
1805          */
1806         if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
1807                 /* FIXME: get_task_mm() increments ->mm_users */
1808                 if (atomic_read(&current->mm->mm_users) > 1)
1809                         return -EINVAL;
1810         }
1811
1812         return 0;
1813 }
1814
1815 /*
1816  * Unshare the filesystem structure if it is being shared
1817  */
1818 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1819 {
1820         struct fs_struct *fs = current->fs;
1821
1822         if (!(unshare_flags & CLONE_FS) || !fs)
1823                 return 0;
1824
1825         /* don't need lock here; in the worst case we'll do useless copy */
1826         if (fs->users == 1)
1827                 return 0;
1828
1829         *new_fsp = copy_fs_struct(fs);
1830         if (!*new_fsp)
1831                 return -ENOMEM;
1832
1833         return 0;
1834 }
1835
1836 /*
1837  * Unshare file descriptor table if it is being shared
1838  */
1839 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1840 {
1841         struct files_struct *fd = current->files;
1842         int error = 0;
1843
1844         if ((unshare_flags & CLONE_FILES) &&
1845             (fd && atomic_read(&fd->count) > 1)) {
1846                 *new_fdp = dup_fd(fd, &error);
1847                 if (!*new_fdp)
1848                         return error;
1849         }
1850
1851         return 0;
1852 }
1853
1854 /*
1855  * unshare allows a process to 'unshare' part of the process
1856  * context which was originally shared using clone.  copy_*
1857  * functions used by do_fork() cannot be used here directly
1858  * because they modify an inactive task_struct that is being
1859  * constructed. Here we are modifying the current, active,
1860  * task_struct.
1861  */
1862 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1863 {
1864         struct fs_struct *fs, *new_fs = NULL;
1865         struct files_struct *fd, *new_fd = NULL;
1866         struct cred *new_cred = NULL;
1867         struct nsproxy *new_nsproxy = NULL;
1868         int do_sysvsem = 0;
1869         int err;
1870
1871         /*
1872          * If unsharing a user namespace must also unshare the thread.
1873          */
1874         if (unshare_flags & CLONE_NEWUSER)
1875                 unshare_flags |= CLONE_THREAD | CLONE_FS;
1876         /*
1877          * If unsharing a thread from a thread group, must also unshare vm.
1878          */
1879         if (unshare_flags & CLONE_THREAD)
1880                 unshare_flags |= CLONE_VM;
1881         /*
1882          * If unsharing vm, must also unshare signal handlers.
1883          */
1884         if (unshare_flags & CLONE_VM)
1885                 unshare_flags |= CLONE_SIGHAND;
1886         /*
1887          * If unsharing namespace, must also unshare filesystem information.
1888          */
1889         if (unshare_flags & CLONE_NEWNS)
1890                 unshare_flags |= CLONE_FS;
1891
1892         err = check_unshare_flags(unshare_flags);
1893         if (err)
1894                 goto bad_unshare_out;
1895         /*
1896          * CLONE_NEWIPC must also detach from the undolist: after switching
1897          * to a new ipc namespace, the semaphore arrays from the old
1898          * namespace are unreachable.
1899          */
1900         if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1901                 do_sysvsem = 1;
1902         err = unshare_fs(unshare_flags, &new_fs);
1903         if (err)
1904                 goto bad_unshare_out;
1905         err = unshare_fd(unshare_flags, &new_fd);
1906         if (err)
1907                 goto bad_unshare_cleanup_fs;
1908         err = unshare_userns(unshare_flags, &new_cred);
1909         if (err)
1910                 goto bad_unshare_cleanup_fd;
1911         err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
1912                                          new_cred, new_fs);
1913         if (err)
1914                 goto bad_unshare_cleanup_cred;
1915
1916         if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
1917                 if (do_sysvsem) {
1918                         /*
1919                          * CLONE_SYSVSEM is equivalent to sys_exit().
1920                          */
1921                         exit_sem(current);
1922                 }
1923                 if (unshare_flags & CLONE_NEWIPC) {
1924                         /* Orphan segments in old ns (see sem above). */
1925                         exit_shm(current);
1926                         shm_init_task(current);
1927                 }
1928
1929                 if (new_nsproxy)
1930                         switch_task_namespaces(current, new_nsproxy);
1931
1932                 task_lock(current);
1933
1934                 if (new_fs) {
1935                         fs = current->fs;
1936                         spin_lock(&fs->lock);
1937                         current->fs = new_fs;
1938                         if (--fs->users)
1939                                 new_fs = NULL;
1940                         else
1941                                 new_fs = fs;
1942                         spin_unlock(&fs->lock);
1943                 }
1944
1945                 if (new_fd) {
1946                         fd = current->files;
1947                         current->files = new_fd;
1948                         new_fd = fd;
1949                 }
1950
1951                 task_unlock(current);
1952
1953                 if (new_cred) {
1954                         /* Install the new user namespace */
1955                         commit_creds(new_cred);
1956                         new_cred = NULL;
1957                 }
1958         }
1959
1960 bad_unshare_cleanup_cred:
1961         if (new_cred)
1962                 put_cred(new_cred);
1963 bad_unshare_cleanup_fd:
1964         if (new_fd)
1965                 put_files_struct(new_fd);
1966
1967 bad_unshare_cleanup_fs:
1968         if (new_fs)
1969                 free_fs_struct(new_fs);
1970
1971 bad_unshare_out:
1972         return err;
1973 }
1974
1975 /*
1976  *      Helper to unshare the files of the current task.
1977  *      We don't want to expose copy_files internals to
1978  *      the exec layer of the kernel.
1979  */
1980
1981 int unshare_files(struct files_struct **displaced)
1982 {
1983         struct task_struct *task = current;
1984         struct files_struct *copy = NULL;
1985         int error;
1986
1987         error = unshare_fd(CLONE_FILES, &copy);
1988         if (error || !copy) {
1989                 *displaced = NULL;
1990                 return error;
1991         }
1992         *displaced = task->files;
1993         task_lock(task);
1994         task->files = copy;
1995         task_unlock(task);
1996         return 0;
1997 }