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