4 * Copyright (C) 1991, 1992 Linus Torvalds
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()'
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>
31 #include <linux/nsproxy.h>
32 #include <linux/capability.h>
33 #include <linux/cpu.h>
34 #include <linux/cgroup.h>
35 #include <linux/security.h>
36 #include <linux/hugetlb.h>
37 #include <linux/swap.h>
38 #include <linux/syscalls.h>
39 #include <linux/jiffies.h>
40 #include <linux/tracehook.h>
41 #include <linux/futex.h>
42 #include <linux/compat.h>
43 #include <linux/task_io_accounting_ops.h>
44 #include <linux/rcupdate.h>
45 #include <linux/ptrace.h>
46 #include <linux/mount.h>
47 #include <linux/audit.h>
48 #include <linux/memcontrol.h>
49 #include <linux/ftrace.h>
50 #include <linux/profile.h>
51 #include <linux/rmap.h>
52 #include <linux/ksm.h>
53 #include <linux/acct.h>
54 #include <linux/tsacct_kern.h>
55 #include <linux/cn_proc.h>
56 #include <linux/freezer.h>
57 #include <linux/delayacct.h>
58 #include <linux/taskstats_kern.h>
59 #include <linux/random.h>
60 #include <linux/tty.h>
61 #include <linux/proc_fs.h>
62 #include <linux/blkdev.h>
63 #include <linux/fs_struct.h>
64 #include <linux/magic.h>
65 #include <linux/perf_event.h>
66 #include <linux/posix-timers.h>
67 #include <linux/user-return-notifier.h>
69 #include <asm/pgtable.h>
70 #include <asm/pgalloc.h>
71 #include <asm/uaccess.h>
72 #include <asm/mmu_context.h>
73 #include <asm/cacheflush.h>
74 #include <asm/tlbflush.h>
76 #include <trace/events/sched.h>
79 * Protected counters by write_lock_irq(&tasklist_lock)
81 unsigned long total_forks; /* Handle normal Linux uptimes. */
82 int nr_threads; /* The idle threads do not count.. */
84 int max_threads; /* tunable limit on nr_threads */
86 DEFINE_PER_CPU(unsigned long, process_counts) = 0;
88 __cacheline_aligned DEFINE_RWLOCK(tasklist_lock); /* outer */
90 #ifdef CONFIG_PROVE_RCU
91 int lockdep_tasklist_lock_is_held(void)
93 return lockdep_is_held(&tasklist_lock);
95 EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
96 #endif /* #ifdef CONFIG_PROVE_RCU */
98 int nr_processes(void)
103 for_each_possible_cpu(cpu)
104 total += per_cpu(process_counts, cpu);
109 #ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
110 # define alloc_task_struct() kmem_cache_alloc(task_struct_cachep, GFP_KERNEL)
111 # define free_task_struct(tsk) kmem_cache_free(task_struct_cachep, (tsk))
112 static struct kmem_cache *task_struct_cachep;
115 #ifndef __HAVE_ARCH_THREAD_INFO_ALLOCATOR
116 static inline struct thread_info *alloc_thread_info(struct task_struct *tsk)
118 #ifdef CONFIG_DEBUG_STACK_USAGE
119 gfp_t mask = GFP_KERNEL | __GFP_ZERO;
121 gfp_t mask = GFP_KERNEL;
123 return (struct thread_info *)__get_free_pages(mask, THREAD_SIZE_ORDER);
126 static inline void free_thread_info(struct thread_info *ti)
128 free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
132 /* SLAB cache for signal_struct structures (tsk->signal) */
133 static struct kmem_cache *signal_cachep;
135 /* SLAB cache for sighand_struct structures (tsk->sighand) */
136 struct kmem_cache *sighand_cachep;
138 /* SLAB cache for files_struct structures (tsk->files) */
139 struct kmem_cache *files_cachep;
141 /* SLAB cache for fs_struct structures (tsk->fs) */
142 struct kmem_cache *fs_cachep;
144 /* SLAB cache for vm_area_struct structures */
145 struct kmem_cache *vm_area_cachep;
147 /* SLAB cache for mm_struct structures (tsk->mm) */
148 static struct kmem_cache *mm_cachep;
150 static void account_kernel_stack(struct thread_info *ti, int account)
152 struct zone *zone = page_zone(virt_to_page(ti));
154 mod_zone_page_state(zone, NR_KERNEL_STACK, account);
157 void free_task(struct task_struct *tsk)
159 prop_local_destroy_single(&tsk->dirties);
160 account_kernel_stack(tsk->stack, -1);
161 free_thread_info(tsk->stack);
162 rt_mutex_debug_task_free(tsk);
163 ftrace_graph_exit_task(tsk);
164 free_task_struct(tsk);
166 EXPORT_SYMBOL(free_task);
168 static inline void free_signal_struct(struct signal_struct *sig)
170 taskstats_tgid_free(sig);
171 kmem_cache_free(signal_cachep, sig);
174 static inline void put_signal_struct(struct signal_struct *sig)
176 if (atomic_dec_and_test(&sig->sigcnt))
177 free_signal_struct(sig);
180 void __put_task_struct(struct task_struct *tsk)
182 WARN_ON(!tsk->exit_state);
183 WARN_ON(atomic_read(&tsk->usage));
184 WARN_ON(tsk == current);
187 delayacct_tsk_free(tsk);
188 put_signal_struct(tsk->signal);
190 if (!profile_handoff_task(tsk))
195 * macro override instead of weak attribute alias, to workaround
196 * gcc 4.1.0 and 4.1.1 bugs with weak attribute and empty functions.
198 #ifndef arch_task_cache_init
199 #define arch_task_cache_init()
202 void __init fork_init(unsigned long mempages)
204 #ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
205 #ifndef ARCH_MIN_TASKALIGN
206 #define ARCH_MIN_TASKALIGN L1_CACHE_BYTES
208 /* create a slab on which task_structs can be allocated */
210 kmem_cache_create("task_struct", sizeof(struct task_struct),
211 ARCH_MIN_TASKALIGN, SLAB_PANIC | SLAB_NOTRACK, NULL);
214 /* do the arch specific task caches init */
215 arch_task_cache_init();
218 * The default maximum number of threads is set to a safe
219 * value: the thread structures can take up at most half
222 max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
225 * we need to allow at least 20 threads to boot a system
230 init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
231 init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
232 init_task.signal->rlim[RLIMIT_SIGPENDING] =
233 init_task.signal->rlim[RLIMIT_NPROC];
236 int __attribute__((weak)) arch_dup_task_struct(struct task_struct *dst,
237 struct task_struct *src)
243 static struct task_struct *dup_task_struct(struct task_struct *orig)
245 struct task_struct *tsk;
246 struct thread_info *ti;
247 unsigned long *stackend;
251 prepare_to_copy(orig);
253 tsk = alloc_task_struct();
257 ti = alloc_thread_info(tsk);
259 free_task_struct(tsk);
263 err = arch_dup_task_struct(tsk, orig);
269 err = prop_local_init_single(&tsk->dirties);
273 setup_thread_stack(tsk, orig);
274 clear_user_return_notifier(tsk);
275 stackend = end_of_stack(tsk);
276 *stackend = STACK_END_MAGIC; /* for overflow detection */
278 #ifdef CONFIG_CC_STACKPROTECTOR
279 tsk->stack_canary = get_random_int();
282 /* One for us, one for whoever does the "release_task()" (usually parent) */
283 atomic_set(&tsk->usage,2);
284 atomic_set(&tsk->fs_excl, 0);
285 #ifdef CONFIG_BLK_DEV_IO_TRACE
288 tsk->splice_pipe = NULL;
290 account_kernel_stack(ti, 1);
295 free_thread_info(ti);
296 free_task_struct(tsk);
301 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
303 struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
304 struct rb_node **rb_link, *rb_parent;
306 unsigned long charge;
307 struct mempolicy *pol;
309 down_write(&oldmm->mmap_sem);
310 flush_cache_dup_mm(oldmm);
312 * Not linked in yet - no deadlock potential:
314 down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
318 mm->mmap_cache = NULL;
319 mm->free_area_cache = oldmm->mmap_base;
320 mm->cached_hole_size = ~0UL;
322 cpumask_clear(mm_cpumask(mm));
324 rb_link = &mm->mm_rb.rb_node;
327 retval = ksm_fork(mm, oldmm);
332 for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
335 if (mpnt->vm_flags & VM_DONTCOPY) {
336 long pages = vma_pages(mpnt);
337 mm->total_vm -= pages;
338 vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
343 if (mpnt->vm_flags & VM_ACCOUNT) {
344 unsigned int len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
345 if (security_vm_enough_memory(len))
349 tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
353 INIT_LIST_HEAD(&tmp->anon_vma_chain);
354 pol = mpol_dup(vma_policy(mpnt));
355 retval = PTR_ERR(pol);
357 goto fail_nomem_policy;
358 vma_set_policy(tmp, pol);
359 if (anon_vma_fork(tmp, mpnt))
360 goto fail_nomem_anon_vma_fork;
361 tmp->vm_flags &= ~VM_LOCKED;
363 tmp->vm_next = tmp->vm_prev = NULL;
366 struct inode *inode = file->f_path.dentry->d_inode;
367 struct address_space *mapping = file->f_mapping;
370 if (tmp->vm_flags & VM_DENYWRITE)
371 atomic_dec(&inode->i_writecount);
372 spin_lock(&mapping->i_mmap_lock);
373 if (tmp->vm_flags & VM_SHARED)
374 mapping->i_mmap_writable++;
375 tmp->vm_truncate_count = mpnt->vm_truncate_count;
376 flush_dcache_mmap_lock(mapping);
377 /* insert tmp into the share list, just after mpnt */
378 vma_prio_tree_add(tmp, mpnt);
379 flush_dcache_mmap_unlock(mapping);
380 spin_unlock(&mapping->i_mmap_lock);
384 * Clear hugetlb-related page reserves for children. This only
385 * affects MAP_PRIVATE mappings. Faults generated by the child
386 * are not guaranteed to succeed, even if read-only
388 if (is_vm_hugetlb_page(tmp))
389 reset_vma_resv_huge_pages(tmp);
392 * Link in the new vma and copy the page table entries.
395 pprev = &tmp->vm_next;
399 __vma_link_rb(mm, tmp, rb_link, rb_parent);
400 rb_link = &tmp->vm_rb.rb_right;
401 rb_parent = &tmp->vm_rb;
404 retval = copy_page_range(mm, oldmm, mpnt);
406 if (tmp->vm_ops && tmp->vm_ops->open)
407 tmp->vm_ops->open(tmp);
412 /* a new mm has just been created */
413 arch_dup_mmap(oldmm, mm);
416 up_write(&mm->mmap_sem);
418 up_write(&oldmm->mmap_sem);
420 fail_nomem_anon_vma_fork:
423 kmem_cache_free(vm_area_cachep, tmp);
426 vm_unacct_memory(charge);
430 static inline int mm_alloc_pgd(struct mm_struct * mm)
432 mm->pgd = pgd_alloc(mm);
433 if (unlikely(!mm->pgd))
438 static inline void mm_free_pgd(struct mm_struct * mm)
440 pgd_free(mm, mm->pgd);
443 #define dup_mmap(mm, oldmm) (0)
444 #define mm_alloc_pgd(mm) (0)
445 #define mm_free_pgd(mm)
446 #endif /* CONFIG_MMU */
448 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
450 #define allocate_mm() (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
451 #define free_mm(mm) (kmem_cache_free(mm_cachep, (mm)))
453 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
455 static int __init coredump_filter_setup(char *s)
457 default_dump_filter =
458 (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
459 MMF_DUMP_FILTER_MASK;
463 __setup("coredump_filter=", coredump_filter_setup);
465 #include <linux/init_task.h>
467 static void mm_init_aio(struct mm_struct *mm)
470 spin_lock_init(&mm->ioctx_lock);
471 INIT_HLIST_HEAD(&mm->ioctx_list);
475 static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
477 atomic_set(&mm->mm_users, 1);
478 atomic_set(&mm->mm_count, 1);
479 init_rwsem(&mm->mmap_sem);
480 INIT_LIST_HEAD(&mm->mmlist);
481 mm->flags = (current->mm) ?
482 (current->mm->flags & MMF_INIT_MASK) : default_dump_filter;
483 mm->core_state = NULL;
485 memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
486 spin_lock_init(&mm->page_table_lock);
487 mm->free_area_cache = TASK_UNMAPPED_BASE;
488 mm->cached_hole_size = ~0UL;
490 mm_init_owner(mm, p);
492 if (likely(!mm_alloc_pgd(mm))) {
494 mmu_notifier_mm_init(mm);
503 * Allocate and initialize an mm_struct.
505 struct mm_struct * mm_alloc(void)
507 struct mm_struct * mm;
511 memset(mm, 0, sizeof(*mm));
512 mm = mm_init(mm, current);
518 * Called when the last reference to the mm
519 * is dropped: either by a lazy thread or by
520 * mmput. Free the page directory and the mm.
522 void __mmdrop(struct mm_struct *mm)
524 BUG_ON(mm == &init_mm);
527 mmu_notifier_mm_destroy(mm);
530 EXPORT_SYMBOL_GPL(__mmdrop);
533 * Decrement the use count and release all resources for an mm.
535 void mmput(struct mm_struct *mm)
539 if (atomic_dec_and_test(&mm->mm_users)) {
543 set_mm_exe_file(mm, NULL);
544 if (!list_empty(&mm->mmlist)) {
545 spin_lock(&mmlist_lock);
546 list_del(&mm->mmlist);
547 spin_unlock(&mmlist_lock);
551 module_put(mm->binfmt->module);
555 EXPORT_SYMBOL_GPL(mmput);
558 * get_task_mm - acquire a reference to the task's mm
560 * Returns %NULL if the task has no mm. Checks PF_KTHREAD (meaning
561 * this kernel workthread has transiently adopted a user mm with use_mm,
562 * to do its AIO) is not set and if so returns a reference to it, after
563 * bumping up the use count. User must release the mm via mmput()
564 * after use. Typically used by /proc and ptrace.
566 struct mm_struct *get_task_mm(struct task_struct *task)
568 struct mm_struct *mm;
573 if (task->flags & PF_KTHREAD)
576 atomic_inc(&mm->mm_users);
581 EXPORT_SYMBOL_GPL(get_task_mm);
583 /* Please note the differences between mmput and mm_release.
584 * mmput is called whenever we stop holding onto a mm_struct,
585 * error success whatever.
587 * mm_release is called after a mm_struct has been removed
588 * from the current process.
590 * This difference is important for error handling, when we
591 * only half set up a mm_struct for a new process and need to restore
592 * the old one. Because we mmput the new mm_struct before
593 * restoring the old one. . .
594 * Eric Biederman 10 January 1998
596 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
598 struct completion *vfork_done = tsk->vfork_done;
600 /* Get rid of any futexes when releasing the mm */
602 if (unlikely(tsk->robust_list)) {
603 exit_robust_list(tsk);
604 tsk->robust_list = NULL;
607 if (unlikely(tsk->compat_robust_list)) {
608 compat_exit_robust_list(tsk);
609 tsk->compat_robust_list = NULL;
612 if (unlikely(!list_empty(&tsk->pi_state_list)))
613 exit_pi_state_list(tsk);
616 /* Get rid of any cached register state */
617 deactivate_mm(tsk, mm);
619 /* notify parent sleeping on vfork() */
621 tsk->vfork_done = NULL;
622 complete(vfork_done);
626 * If we're exiting normally, clear a user-space tid field if
627 * requested. We leave this alone when dying by signal, to leave
628 * the value intact in a core dump, and to save the unnecessary
629 * trouble otherwise. Userland only wants this done for a sys_exit.
631 if (tsk->clear_child_tid) {
632 if (!(tsk->flags & PF_SIGNALED) &&
633 atomic_read(&mm->mm_users) > 1) {
635 * We don't check the error code - if userspace has
636 * not set up a proper pointer then tough luck.
638 put_user(0, tsk->clear_child_tid);
639 sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
642 tsk->clear_child_tid = NULL;
647 * Allocate a new mm structure and copy contents from the
648 * mm structure of the passed in task structure.
650 struct mm_struct *dup_mm(struct task_struct *tsk)
652 struct mm_struct *mm, *oldmm = current->mm;
662 memcpy(mm, oldmm, sizeof(*mm));
664 /* Initializing for Swap token stuff */
665 mm->token_priority = 0;
666 mm->last_interval = 0;
668 if (!mm_init(mm, tsk))
671 if (init_new_context(tsk, mm))
674 dup_mm_exe_file(oldmm, mm);
676 err = dup_mmap(mm, oldmm);
680 mm->hiwater_rss = get_mm_rss(mm);
681 mm->hiwater_vm = mm->total_vm;
683 if (mm->binfmt && !try_module_get(mm->binfmt->module))
689 /* don't put binfmt in mmput, we haven't got module yet */
698 * If init_new_context() failed, we cannot use mmput() to free the mm
699 * because it calls destroy_context()
706 static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
708 struct mm_struct * mm, *oldmm;
711 tsk->min_flt = tsk->maj_flt = 0;
712 tsk->nvcsw = tsk->nivcsw = 0;
713 #ifdef CONFIG_DETECT_HUNG_TASK
714 tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
718 tsk->active_mm = NULL;
721 * Are we cloning a kernel thread?
723 * We need to steal a active VM for that..
729 if (clone_flags & CLONE_VM) {
730 atomic_inc(&oldmm->mm_users);
741 /* Initializing for Swap token stuff */
742 mm->token_priority = 0;
743 mm->last_interval = 0;
753 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
755 struct fs_struct *fs = current->fs;
756 if (clone_flags & CLONE_FS) {
757 /* tsk->fs is already what we want */
758 write_lock(&fs->lock);
760 write_unlock(&fs->lock);
764 write_unlock(&fs->lock);
767 tsk->fs = copy_fs_struct(fs);
773 static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
775 struct files_struct *oldf, *newf;
779 * A background process may not have any files ...
781 oldf = current->files;
785 if (clone_flags & CLONE_FILES) {
786 atomic_inc(&oldf->count);
790 newf = dup_fd(oldf, &error);
800 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
803 struct io_context *ioc = current->io_context;
808 * Share io context with parent, if CLONE_IO is set
810 if (clone_flags & CLONE_IO) {
811 tsk->io_context = ioc_task_link(ioc);
812 if (unlikely(!tsk->io_context))
814 } else if (ioprio_valid(ioc->ioprio)) {
815 tsk->io_context = alloc_io_context(GFP_KERNEL, -1);
816 if (unlikely(!tsk->io_context))
819 tsk->io_context->ioprio = ioc->ioprio;
825 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
827 struct sighand_struct *sig;
829 if (clone_flags & CLONE_SIGHAND) {
830 atomic_inc(¤t->sighand->count);
833 sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
834 rcu_assign_pointer(tsk->sighand, sig);
837 atomic_set(&sig->count, 1);
838 memcpy(sig->action, current->sighand->action, sizeof(sig->action));
842 void __cleanup_sighand(struct sighand_struct *sighand)
844 if (atomic_dec_and_test(&sighand->count))
845 kmem_cache_free(sighand_cachep, sighand);
850 * Initialize POSIX timer handling for a thread group.
852 static void posix_cpu_timers_init_group(struct signal_struct *sig)
854 unsigned long cpu_limit;
856 /* Thread group counters. */
857 thread_group_cputime_init(sig);
859 cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
860 if (cpu_limit != RLIM_INFINITY) {
861 sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
862 sig->cputimer.running = 1;
865 /* The timer lists. */
866 INIT_LIST_HEAD(&sig->cpu_timers[0]);
867 INIT_LIST_HEAD(&sig->cpu_timers[1]);
868 INIT_LIST_HEAD(&sig->cpu_timers[2]);
871 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
873 struct signal_struct *sig;
875 if (clone_flags & CLONE_THREAD)
878 sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
884 atomic_set(&sig->live, 1);
885 atomic_set(&sig->sigcnt, 1);
886 init_waitqueue_head(&sig->wait_chldexit);
887 if (clone_flags & CLONE_NEWPID)
888 sig->flags |= SIGNAL_UNKILLABLE;
889 sig->curr_target = tsk;
890 init_sigpending(&sig->shared_pending);
891 INIT_LIST_HEAD(&sig->posix_timers);
893 hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
894 sig->real_timer.function = it_real_fn;
896 task_lock(current->group_leader);
897 memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
898 task_unlock(current->group_leader);
900 posix_cpu_timers_init_group(sig);
904 sig->oom_adj = current->signal->oom_adj;
909 static void copy_flags(unsigned long clone_flags, struct task_struct *p)
911 unsigned long new_flags = p->flags;
913 new_flags &= ~PF_SUPERPRIV;
914 new_flags |= PF_FORKNOEXEC;
915 new_flags |= PF_STARTING;
916 p->flags = new_flags;
917 clear_freeze_flag(p);
920 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
922 current->clear_child_tid = tidptr;
924 return task_pid_vnr(current);
927 static void rt_mutex_init_task(struct task_struct *p)
929 raw_spin_lock_init(&p->pi_lock);
930 #ifdef CONFIG_RT_MUTEXES
931 plist_head_init_raw(&p->pi_waiters, &p->pi_lock);
932 p->pi_blocked_on = NULL;
936 #ifdef CONFIG_MM_OWNER
937 void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
941 #endif /* CONFIG_MM_OWNER */
944 * Initialize POSIX timer handling for a single task.
946 static void posix_cpu_timers_init(struct task_struct *tsk)
948 tsk->cputime_expires.prof_exp = cputime_zero;
949 tsk->cputime_expires.virt_exp = cputime_zero;
950 tsk->cputime_expires.sched_exp = 0;
951 INIT_LIST_HEAD(&tsk->cpu_timers[0]);
952 INIT_LIST_HEAD(&tsk->cpu_timers[1]);
953 INIT_LIST_HEAD(&tsk->cpu_timers[2]);
957 * This creates a new process as a copy of the old one,
958 * but does not actually start it yet.
960 * It copies the registers, and all the appropriate
961 * parts of the process environment (as per the clone
962 * flags). The actual kick-off is left to the caller.
964 static struct task_struct *copy_process(unsigned long clone_flags,
965 unsigned long stack_start,
966 struct pt_regs *regs,
967 unsigned long stack_size,
968 int __user *child_tidptr,
973 struct task_struct *p;
974 int cgroup_callbacks_done = 0;
976 if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
977 return ERR_PTR(-EINVAL);
980 * Thread groups must share signals as well, and detached threads
981 * can only be started up within the thread group.
983 if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
984 return ERR_PTR(-EINVAL);
987 * Shared signal handlers imply shared VM. By way of the above,
988 * thread groups also imply shared VM. Blocking this case allows
989 * for various simplifications in other code.
991 if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
992 return ERR_PTR(-EINVAL);
995 * Siblings of global init remain as zombies on exit since they are
996 * not reaped by their parent (swapper). To solve this and to avoid
997 * multi-rooted process trees, prevent global and container-inits
998 * from creating siblings.
1000 if ((clone_flags & CLONE_PARENT) &&
1001 current->signal->flags & SIGNAL_UNKILLABLE)
1002 return ERR_PTR(-EINVAL);
1004 retval = security_task_create(clone_flags);
1009 p = dup_task_struct(current);
1013 ftrace_graph_init_task(p);
1015 rt_mutex_init_task(p);
1017 #ifdef CONFIG_PROVE_LOCKING
1018 DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1019 DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1022 if (atomic_read(&p->real_cred->user->processes) >=
1023 task_rlimit(p, RLIMIT_NPROC)) {
1024 if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
1025 p->real_cred->user != INIT_USER)
1029 retval = copy_creds(p, clone_flags);
1034 * If multiple threads are within copy_process(), then this check
1035 * triggers too late. This doesn't hurt, the check is only there
1036 * to stop root fork bombs.
1039 if (nr_threads >= max_threads)
1040 goto bad_fork_cleanup_count;
1042 if (!try_module_get(task_thread_info(p)->exec_domain->module))
1043 goto bad_fork_cleanup_count;
1046 delayacct_tsk_init(p); /* Must remain after dup_task_struct() */
1047 copy_flags(clone_flags, p);
1048 INIT_LIST_HEAD(&p->children);
1049 INIT_LIST_HEAD(&p->sibling);
1050 rcu_copy_process(p);
1051 p->vfork_done = NULL;
1052 spin_lock_init(&p->alloc_lock);
1054 init_sigpending(&p->pending);
1056 p->utime = cputime_zero;
1057 p->stime = cputime_zero;
1058 p->gtime = cputime_zero;
1059 p->utimescaled = cputime_zero;
1060 p->stimescaled = cputime_zero;
1061 #ifndef CONFIG_VIRT_CPU_ACCOUNTING
1062 p->prev_utime = cputime_zero;
1063 p->prev_stime = cputime_zero;
1065 #if defined(SPLIT_RSS_COUNTING)
1066 memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1069 p->default_timer_slack_ns = current->timer_slack_ns;
1071 task_io_accounting_init(&p->ioac);
1072 acct_clear_integrals(p);
1074 posix_cpu_timers_init(p);
1076 p->lock_depth = -1; /* -1 = no lock */
1077 do_posix_clock_monotonic_gettime(&p->start_time);
1078 p->real_start_time = p->start_time;
1079 monotonic_to_bootbased(&p->real_start_time);
1080 p->io_context = NULL;
1081 p->audit_context = NULL;
1084 p->mempolicy = mpol_dup(p->mempolicy);
1085 if (IS_ERR(p->mempolicy)) {
1086 retval = PTR_ERR(p->mempolicy);
1087 p->mempolicy = NULL;
1088 goto bad_fork_cleanup_cgroup;
1090 mpol_fix_fork_child_flag(p);
1092 #ifdef CONFIG_TRACE_IRQFLAGS
1094 #ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
1095 p->hardirqs_enabled = 1;
1097 p->hardirqs_enabled = 0;
1099 p->hardirq_enable_ip = 0;
1100 p->hardirq_enable_event = 0;
1101 p->hardirq_disable_ip = _THIS_IP_;
1102 p->hardirq_disable_event = 0;
1103 p->softirqs_enabled = 1;
1104 p->softirq_enable_ip = _THIS_IP_;
1105 p->softirq_enable_event = 0;
1106 p->softirq_disable_ip = 0;
1107 p->softirq_disable_event = 0;
1108 p->hardirq_context = 0;
1109 p->softirq_context = 0;
1111 #ifdef CONFIG_LOCKDEP
1112 p->lockdep_depth = 0; /* no locks held yet */
1113 p->curr_chain_key = 0;
1114 p->lockdep_recursion = 0;
1117 #ifdef CONFIG_DEBUG_MUTEXES
1118 p->blocked_on = NULL; /* not blocked yet */
1120 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
1121 p->memcg_batch.do_batch = 0;
1122 p->memcg_batch.memcg = NULL;
1125 /* Perform scheduler related setup. Assign this task to a CPU. */
1126 sched_fork(p, clone_flags);
1128 retval = perf_event_init_task(p);
1130 goto bad_fork_cleanup_policy;
1132 if ((retval = audit_alloc(p)))
1133 goto bad_fork_cleanup_policy;
1134 /* copy all the process information */
1135 if ((retval = copy_semundo(clone_flags, p)))
1136 goto bad_fork_cleanup_audit;
1137 if ((retval = copy_files(clone_flags, p)))
1138 goto bad_fork_cleanup_semundo;
1139 if ((retval = copy_fs(clone_flags, p)))
1140 goto bad_fork_cleanup_files;
1141 if ((retval = copy_sighand(clone_flags, p)))
1142 goto bad_fork_cleanup_fs;
1143 if ((retval = copy_signal(clone_flags, p)))
1144 goto bad_fork_cleanup_sighand;
1145 if ((retval = copy_mm(clone_flags, p)))
1146 goto bad_fork_cleanup_signal;
1147 if ((retval = copy_namespaces(clone_flags, p)))
1148 goto bad_fork_cleanup_mm;
1149 if ((retval = copy_io(clone_flags, p)))
1150 goto bad_fork_cleanup_namespaces;
1151 retval = copy_thread(clone_flags, stack_start, stack_size, p, regs);
1153 goto bad_fork_cleanup_io;
1155 if (pid != &init_struct_pid) {
1157 pid = alloc_pid(p->nsproxy->pid_ns);
1159 goto bad_fork_cleanup_io;
1161 if (clone_flags & CLONE_NEWPID) {
1162 retval = pid_ns_prepare_proc(p->nsproxy->pid_ns);
1164 goto bad_fork_free_pid;
1168 p->pid = pid_nr(pid);
1170 if (clone_flags & CLONE_THREAD)
1171 p->tgid = current->tgid;
1173 if (current->nsproxy != p->nsproxy) {
1174 retval = ns_cgroup_clone(p, pid);
1176 goto bad_fork_free_pid;
1179 p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1181 * Clear TID on mm_release()?
1183 p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr: NULL;
1185 p->robust_list = NULL;
1186 #ifdef CONFIG_COMPAT
1187 p->compat_robust_list = NULL;
1189 INIT_LIST_HEAD(&p->pi_state_list);
1190 p->pi_state_cache = NULL;
1193 * sigaltstack should be cleared when sharing the same VM
1195 if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1196 p->sas_ss_sp = p->sas_ss_size = 0;
1199 * Syscall tracing and stepping should be turned off in the
1200 * child regardless of CLONE_PTRACE.
1202 user_disable_single_step(p);
1203 clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1204 #ifdef TIF_SYSCALL_EMU
1205 clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1207 clear_all_latency_tracing(p);
1209 /* ok, now we should be set up.. */
1210 p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
1211 p->pdeath_signal = 0;
1215 * Ok, make it visible to the rest of the system.
1216 * We dont wake it up yet.
1218 p->group_leader = p;
1219 INIT_LIST_HEAD(&p->thread_group);
1221 /* Now that the task is set up, run cgroup callbacks if
1222 * necessary. We need to run them before the task is visible
1223 * on the tasklist. */
1224 cgroup_fork_callbacks(p);
1225 cgroup_callbacks_done = 1;
1227 /* Need tasklist lock for parent etc handling! */
1228 write_lock_irq(&tasklist_lock);
1230 /* CLONE_PARENT re-uses the old parent */
1231 if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1232 p->real_parent = current->real_parent;
1233 p->parent_exec_id = current->parent_exec_id;
1235 p->real_parent = current;
1236 p->parent_exec_id = current->self_exec_id;
1239 spin_lock(¤t->sighand->siglock);
1242 * Process group and session signals need to be delivered to just the
1243 * parent before the fork or both the parent and the child after the
1244 * fork. Restart if a signal comes in before we add the new process to
1245 * it's process group.
1246 * A fatal signal pending means that current will exit, so the new
1247 * thread can't slip out of an OOM kill (or normal SIGKILL).
1249 recalc_sigpending();
1250 if (signal_pending(current)) {
1251 spin_unlock(¤t->sighand->siglock);
1252 write_unlock_irq(&tasklist_lock);
1253 retval = -ERESTARTNOINTR;
1254 goto bad_fork_free_pid;
1257 if (clone_flags & CLONE_THREAD) {
1258 current->signal->nr_threads++;
1259 atomic_inc(¤t->signal->live);
1260 atomic_inc(¤t->signal->sigcnt);
1261 p->group_leader = current->group_leader;
1262 list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);
1265 if (likely(p->pid)) {
1266 tracehook_finish_clone(p, clone_flags, trace);
1268 if (thread_group_leader(p)) {
1269 if (clone_flags & CLONE_NEWPID)
1270 p->nsproxy->pid_ns->child_reaper = p;
1272 p->signal->leader_pid = pid;
1273 p->signal->tty = tty_kref_get(current->signal->tty);
1274 attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
1275 attach_pid(p, PIDTYPE_SID, task_session(current));
1276 list_add_tail(&p->sibling, &p->real_parent->children);
1277 list_add_tail_rcu(&p->tasks, &init_task.tasks);
1278 __get_cpu_var(process_counts)++;
1280 attach_pid(p, PIDTYPE_PID, pid);
1285 spin_unlock(¤t->sighand->siglock);
1286 write_unlock_irq(&tasklist_lock);
1287 proc_fork_connector(p);
1288 cgroup_post_fork(p);
1293 if (pid != &init_struct_pid)
1295 bad_fork_cleanup_io:
1298 bad_fork_cleanup_namespaces:
1299 exit_task_namespaces(p);
1300 bad_fork_cleanup_mm:
1303 bad_fork_cleanup_signal:
1304 if (!(clone_flags & CLONE_THREAD))
1305 free_signal_struct(p->signal);
1306 bad_fork_cleanup_sighand:
1307 __cleanup_sighand(p->sighand);
1308 bad_fork_cleanup_fs:
1309 exit_fs(p); /* blocking */
1310 bad_fork_cleanup_files:
1311 exit_files(p); /* blocking */
1312 bad_fork_cleanup_semundo:
1314 bad_fork_cleanup_audit:
1316 bad_fork_cleanup_policy:
1317 perf_event_free_task(p);
1319 mpol_put(p->mempolicy);
1320 bad_fork_cleanup_cgroup:
1322 cgroup_exit(p, cgroup_callbacks_done);
1323 delayacct_tsk_free(p);
1324 module_put(task_thread_info(p)->exec_domain->module);
1325 bad_fork_cleanup_count:
1326 atomic_dec(&p->cred->user->processes);
1331 return ERR_PTR(retval);
1334 noinline struct pt_regs * __cpuinit __attribute__((weak)) idle_regs(struct pt_regs *regs)
1336 memset(regs, 0, sizeof(struct pt_regs));
1340 static inline void init_idle_pids(struct pid_link *links)
1344 for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1345 INIT_HLIST_NODE(&links[type].node); /* not really needed */
1346 links[type].pid = &init_struct_pid;
1350 struct task_struct * __cpuinit fork_idle(int cpu)
1352 struct task_struct *task;
1353 struct pt_regs regs;
1355 task = copy_process(CLONE_VM, 0, idle_regs(®s), 0, NULL,
1356 &init_struct_pid, 0);
1357 if (!IS_ERR(task)) {
1358 init_idle_pids(task->pids);
1359 init_idle(task, cpu);
1366 * Ok, this is the main fork-routine.
1368 * It copies the process, and if successful kick-starts
1369 * it and waits for it to finish using the VM if required.
1371 long do_fork(unsigned long clone_flags,
1372 unsigned long stack_start,
1373 struct pt_regs *regs,
1374 unsigned long stack_size,
1375 int __user *parent_tidptr,
1376 int __user *child_tidptr)
1378 struct task_struct *p;
1383 * Do some preliminary argument and permissions checking before we
1384 * actually start allocating stuff
1386 if (clone_flags & CLONE_NEWUSER) {
1387 if (clone_flags & CLONE_THREAD)
1389 /* hopefully this check will go away when userns support is
1392 if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SETUID) ||
1393 !capable(CAP_SETGID))
1398 * We hope to recycle these flags after 2.6.26
1400 if (unlikely(clone_flags & CLONE_STOPPED)) {
1401 static int __read_mostly count = 100;
1403 if (count > 0 && printk_ratelimit()) {
1404 char comm[TASK_COMM_LEN];
1407 printk(KERN_INFO "fork(): process `%s' used deprecated "
1408 "clone flags 0x%lx\n",
1409 get_task_comm(comm, current),
1410 clone_flags & CLONE_STOPPED);
1415 * When called from kernel_thread, don't do user tracing stuff.
1417 if (likely(user_mode(regs)))
1418 trace = tracehook_prepare_clone(clone_flags);
1420 p = copy_process(clone_flags, stack_start, regs, stack_size,
1421 child_tidptr, NULL, trace);
1423 * Do this prior waking up the new thread - the thread pointer
1424 * might get invalid after that point, if the thread exits quickly.
1427 struct completion vfork;
1429 trace_sched_process_fork(current, p);
1431 nr = task_pid_vnr(p);
1433 if (clone_flags & CLONE_PARENT_SETTID)
1434 put_user(nr, parent_tidptr);
1436 if (clone_flags & CLONE_VFORK) {
1437 p->vfork_done = &vfork;
1438 init_completion(&vfork);
1441 audit_finish_fork(p);
1442 tracehook_report_clone(regs, clone_flags, nr, p);
1445 * We set PF_STARTING at creation in case tracing wants to
1446 * use this to distinguish a fully live task from one that
1447 * hasn't gotten to tracehook_report_clone() yet. Now we
1448 * clear it and set the child going.
1450 p->flags &= ~PF_STARTING;
1452 if (unlikely(clone_flags & CLONE_STOPPED)) {
1454 * We'll start up with an immediate SIGSTOP.
1456 sigaddset(&p->pending.signal, SIGSTOP);
1457 set_tsk_thread_flag(p, TIF_SIGPENDING);
1458 __set_task_state(p, TASK_STOPPED);
1460 wake_up_new_task(p, clone_flags);
1463 tracehook_report_clone_complete(trace, regs,
1464 clone_flags, nr, p);
1466 if (clone_flags & CLONE_VFORK) {
1467 freezer_do_not_count();
1468 wait_for_completion(&vfork);
1470 tracehook_report_vfork_done(p, nr);
1478 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1479 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1482 static void sighand_ctor(void *data)
1484 struct sighand_struct *sighand = data;
1486 spin_lock_init(&sighand->siglock);
1487 init_waitqueue_head(&sighand->signalfd_wqh);
1490 void __init proc_caches_init(void)
1492 sighand_cachep = kmem_cache_create("sighand_cache",
1493 sizeof(struct sighand_struct), 0,
1494 SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1495 SLAB_NOTRACK, sighand_ctor);
1496 signal_cachep = kmem_cache_create("signal_cache",
1497 sizeof(struct signal_struct), 0,
1498 SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1499 files_cachep = kmem_cache_create("files_cache",
1500 sizeof(struct files_struct), 0,
1501 SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1502 fs_cachep = kmem_cache_create("fs_cache",
1503 sizeof(struct fs_struct), 0,
1504 SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1505 mm_cachep = kmem_cache_create("mm_struct",
1506 sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1507 SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1508 vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1513 * Check constraints on flags passed to the unshare system call and
1514 * force unsharing of additional process context as appropriate.
1516 static void check_unshare_flags(unsigned long *flags_ptr)
1519 * If unsharing a thread from a thread group, must also
1522 if (*flags_ptr & CLONE_THREAD)
1523 *flags_ptr |= CLONE_VM;
1526 * If unsharing vm, must also unshare signal handlers.
1528 if (*flags_ptr & CLONE_VM)
1529 *flags_ptr |= CLONE_SIGHAND;
1532 * If unsharing namespace, must also unshare filesystem information.
1534 if (*flags_ptr & CLONE_NEWNS)
1535 *flags_ptr |= CLONE_FS;
1539 * Unsharing of tasks created with CLONE_THREAD is not supported yet
1541 static int unshare_thread(unsigned long unshare_flags)
1543 if (unshare_flags & CLONE_THREAD)
1550 * Unshare the filesystem structure if it is being shared
1552 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1554 struct fs_struct *fs = current->fs;
1556 if (!(unshare_flags & CLONE_FS) || !fs)
1559 /* don't need lock here; in the worst case we'll do useless copy */
1563 *new_fsp = copy_fs_struct(fs);
1571 * Unsharing of sighand is not supported yet
1573 static int unshare_sighand(unsigned long unshare_flags, struct sighand_struct **new_sighp)
1575 struct sighand_struct *sigh = current->sighand;
1577 if ((unshare_flags & CLONE_SIGHAND) && atomic_read(&sigh->count) > 1)
1584 * Unshare vm if it is being shared
1586 static int unshare_vm(unsigned long unshare_flags, struct mm_struct **new_mmp)
1588 struct mm_struct *mm = current->mm;
1590 if ((unshare_flags & CLONE_VM) &&
1591 (mm && atomic_read(&mm->mm_users) > 1)) {
1599 * Unshare file descriptor table if it is being shared
1601 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1603 struct files_struct *fd = current->files;
1606 if ((unshare_flags & CLONE_FILES) &&
1607 (fd && atomic_read(&fd->count) > 1)) {
1608 *new_fdp = dup_fd(fd, &error);
1617 * unshare allows a process to 'unshare' part of the process
1618 * context which was originally shared using clone. copy_*
1619 * functions used by do_fork() cannot be used here directly
1620 * because they modify an inactive task_struct that is being
1621 * constructed. Here we are modifying the current, active,
1624 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1627 struct fs_struct *fs, *new_fs = NULL;
1628 struct sighand_struct *new_sigh = NULL;
1629 struct mm_struct *mm, *new_mm = NULL, *active_mm = NULL;
1630 struct files_struct *fd, *new_fd = NULL;
1631 struct nsproxy *new_nsproxy = NULL;
1634 check_unshare_flags(&unshare_flags);
1636 /* Return -EINVAL for all unsupported flags */
1638 if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1639 CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1640 CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET))
1641 goto bad_unshare_out;
1644 * CLONE_NEWIPC must also detach from the undolist: after switching
1645 * to a new ipc namespace, the semaphore arrays from the old
1646 * namespace are unreachable.
1648 if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1650 if ((err = unshare_thread(unshare_flags)))
1651 goto bad_unshare_out;
1652 if ((err = unshare_fs(unshare_flags, &new_fs)))
1653 goto bad_unshare_cleanup_thread;
1654 if ((err = unshare_sighand(unshare_flags, &new_sigh)))
1655 goto bad_unshare_cleanup_fs;
1656 if ((err = unshare_vm(unshare_flags, &new_mm)))
1657 goto bad_unshare_cleanup_sigh;
1658 if ((err = unshare_fd(unshare_flags, &new_fd)))
1659 goto bad_unshare_cleanup_vm;
1660 if ((err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
1662 goto bad_unshare_cleanup_fd;
1664 if (new_fs || new_mm || new_fd || do_sysvsem || new_nsproxy) {
1667 * CLONE_SYSVSEM is equivalent to sys_exit().
1673 switch_task_namespaces(current, new_nsproxy);
1681 write_lock(&fs->lock);
1682 current->fs = new_fs;
1687 write_unlock(&fs->lock);
1692 active_mm = current->active_mm;
1693 current->mm = new_mm;
1694 current->active_mm = new_mm;
1695 activate_mm(active_mm, new_mm);
1700 fd = current->files;
1701 current->files = new_fd;
1705 task_unlock(current);
1709 put_nsproxy(new_nsproxy);
1711 bad_unshare_cleanup_fd:
1713 put_files_struct(new_fd);
1715 bad_unshare_cleanup_vm:
1719 bad_unshare_cleanup_sigh:
1721 if (atomic_dec_and_test(&new_sigh->count))
1722 kmem_cache_free(sighand_cachep, new_sigh);
1724 bad_unshare_cleanup_fs:
1726 free_fs_struct(new_fs);
1728 bad_unshare_cleanup_thread:
1734 * Helper to unshare the files of the current task.
1735 * We don't want to expose copy_files internals to
1736 * the exec layer of the kernel.
1739 int unshare_files(struct files_struct **displaced)
1741 struct task_struct *task = current;
1742 struct files_struct *copy = NULL;
1745 error = unshare_fd(CLONE_FILES, ©);
1746 if (error || !copy) {
1750 *displaced = task->files;