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>
67 #include <asm/pgtable.h>
68 #include <asm/pgalloc.h>
69 #include <asm/uaccess.h>
70 #include <asm/mmu_context.h>
71 #include <asm/cacheflush.h>
72 #include <asm/tlbflush.h>
74 #include <trace/events/sched.h>
77 * Protected counters by write_lock_irq(&tasklist_lock)
79 unsigned long total_forks; /* Handle normal Linux uptimes. */
80 int nr_threads; /* The idle threads do not count.. */
82 int max_threads; /* tunable limit on nr_threads */
84 DEFINE_PER_CPU(unsigned long, process_counts) = 0;
86 __cacheline_aligned DEFINE_RWLOCK(tasklist_lock); /* outer */
88 int nr_processes(void)
93 for_each_online_cpu(cpu)
94 total += per_cpu(process_counts, cpu);
99 #ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
100 # define alloc_task_struct() kmem_cache_alloc(task_struct_cachep, GFP_KERNEL)
101 # define free_task_struct(tsk) kmem_cache_free(task_struct_cachep, (tsk))
102 static struct kmem_cache *task_struct_cachep;
105 #ifndef __HAVE_ARCH_THREAD_INFO_ALLOCATOR
106 static inline struct thread_info *alloc_thread_info(struct task_struct *tsk)
108 #ifdef CONFIG_DEBUG_STACK_USAGE
109 gfp_t mask = GFP_KERNEL | __GFP_ZERO;
111 gfp_t mask = GFP_KERNEL;
113 return (struct thread_info *)__get_free_pages(mask, THREAD_SIZE_ORDER);
116 static inline void free_thread_info(struct thread_info *ti)
118 free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
122 /* SLAB cache for signal_struct structures (tsk->signal) */
123 static struct kmem_cache *signal_cachep;
125 /* SLAB cache for sighand_struct structures (tsk->sighand) */
126 struct kmem_cache *sighand_cachep;
128 /* SLAB cache for files_struct structures (tsk->files) */
129 struct kmem_cache *files_cachep;
131 /* SLAB cache for fs_struct structures (tsk->fs) */
132 struct kmem_cache *fs_cachep;
134 /* SLAB cache for vm_area_struct structures */
135 struct kmem_cache *vm_area_cachep;
137 /* SLAB cache for mm_struct structures (tsk->mm) */
138 static struct kmem_cache *mm_cachep;
140 static void account_kernel_stack(struct thread_info *ti, int account)
142 struct zone *zone = page_zone(virt_to_page(ti));
144 mod_zone_page_state(zone, NR_KERNEL_STACK, account);
147 void free_task(struct task_struct *tsk)
149 prop_local_destroy_single(&tsk->dirties);
150 account_kernel_stack(tsk->stack, -1);
151 free_thread_info(tsk->stack);
152 rt_mutex_debug_task_free(tsk);
153 ftrace_graph_exit_task(tsk);
154 free_task_struct(tsk);
156 EXPORT_SYMBOL(free_task);
158 void __put_task_struct(struct task_struct *tsk)
160 WARN_ON(!tsk->exit_state);
161 WARN_ON(atomic_read(&tsk->usage));
162 WARN_ON(tsk == current);
165 delayacct_tsk_free(tsk);
167 if (!profile_handoff_task(tsk))
172 * macro override instead of weak attribute alias, to workaround
173 * gcc 4.1.0 and 4.1.1 bugs with weak attribute and empty functions.
175 #ifndef arch_task_cache_init
176 #define arch_task_cache_init()
179 void __init fork_init(unsigned long mempages)
181 #ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
182 #ifndef ARCH_MIN_TASKALIGN
183 #define ARCH_MIN_TASKALIGN L1_CACHE_BYTES
185 /* create a slab on which task_structs can be allocated */
187 kmem_cache_create("task_struct", sizeof(struct task_struct),
188 ARCH_MIN_TASKALIGN, SLAB_PANIC | SLAB_NOTRACK, NULL);
191 /* do the arch specific task caches init */
192 arch_task_cache_init();
195 * The default maximum number of threads is set to a safe
196 * value: the thread structures can take up at most half
199 max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
202 * we need to allow at least 20 threads to boot a system
207 init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
208 init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
209 init_task.signal->rlim[RLIMIT_SIGPENDING] =
210 init_task.signal->rlim[RLIMIT_NPROC];
213 int __attribute__((weak)) arch_dup_task_struct(struct task_struct *dst,
214 struct task_struct *src)
220 static struct task_struct *dup_task_struct(struct task_struct *orig)
222 struct task_struct *tsk;
223 struct thread_info *ti;
224 unsigned long *stackend;
228 prepare_to_copy(orig);
230 tsk = alloc_task_struct();
234 ti = alloc_thread_info(tsk);
236 free_task_struct(tsk);
240 err = arch_dup_task_struct(tsk, orig);
246 err = prop_local_init_single(&tsk->dirties);
250 setup_thread_stack(tsk, orig);
251 stackend = end_of_stack(tsk);
252 *stackend = STACK_END_MAGIC; /* for overflow detection */
254 #ifdef CONFIG_CC_STACKPROTECTOR
255 tsk->stack_canary = get_random_int();
258 /* One for us, one for whoever does the "release_task()" (usually parent) */
259 atomic_set(&tsk->usage,2);
260 atomic_set(&tsk->fs_excl, 0);
261 #ifdef CONFIG_BLK_DEV_IO_TRACE
264 tsk->splice_pipe = NULL;
266 account_kernel_stack(ti, 1);
271 free_thread_info(ti);
272 free_task_struct(tsk);
277 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
279 struct vm_area_struct *mpnt, *tmp, **pprev;
280 struct rb_node **rb_link, *rb_parent;
282 unsigned long charge;
283 struct mempolicy *pol;
285 down_write(&oldmm->mmap_sem);
286 flush_cache_dup_mm(oldmm);
288 * Not linked in yet - no deadlock potential:
290 down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
294 mm->mmap_cache = NULL;
295 mm->free_area_cache = oldmm->mmap_base;
296 mm->cached_hole_size = ~0UL;
298 cpumask_clear(mm_cpumask(mm));
300 rb_link = &mm->mm_rb.rb_node;
303 retval = ksm_fork(mm, oldmm);
307 for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
310 if (mpnt->vm_flags & VM_DONTCOPY) {
311 long pages = vma_pages(mpnt);
312 mm->total_vm -= pages;
313 vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
318 if (mpnt->vm_flags & VM_ACCOUNT) {
319 unsigned int len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
320 if (security_vm_enough_memory(len))
324 tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
328 pol = mpol_dup(vma_policy(mpnt));
329 retval = PTR_ERR(pol);
331 goto fail_nomem_policy;
332 vma_set_policy(tmp, pol);
333 tmp->vm_flags &= ~VM_LOCKED;
339 struct inode *inode = file->f_path.dentry->d_inode;
340 struct address_space *mapping = file->f_mapping;
343 if (tmp->vm_flags & VM_DENYWRITE)
344 atomic_dec(&inode->i_writecount);
345 spin_lock(&mapping->i_mmap_lock);
346 if (tmp->vm_flags & VM_SHARED)
347 mapping->i_mmap_writable++;
348 tmp->vm_truncate_count = mpnt->vm_truncate_count;
349 flush_dcache_mmap_lock(mapping);
350 /* insert tmp into the share list, just after mpnt */
351 vma_prio_tree_add(tmp, mpnt);
352 flush_dcache_mmap_unlock(mapping);
353 spin_unlock(&mapping->i_mmap_lock);
357 * Clear hugetlb-related page reserves for children. This only
358 * affects MAP_PRIVATE mappings. Faults generated by the child
359 * are not guaranteed to succeed, even if read-only
361 if (is_vm_hugetlb_page(tmp))
362 reset_vma_resv_huge_pages(tmp);
365 * Link in the new vma and copy the page table entries.
368 pprev = &tmp->vm_next;
370 __vma_link_rb(mm, tmp, rb_link, rb_parent);
371 rb_link = &tmp->vm_rb.rb_right;
372 rb_parent = &tmp->vm_rb;
375 retval = copy_page_range(mm, oldmm, mpnt);
377 if (tmp->vm_ops && tmp->vm_ops->open)
378 tmp->vm_ops->open(tmp);
383 /* a new mm has just been created */
384 arch_dup_mmap(oldmm, mm);
387 up_write(&mm->mmap_sem);
389 up_write(&oldmm->mmap_sem);
392 kmem_cache_free(vm_area_cachep, tmp);
395 vm_unacct_memory(charge);
399 static inline int mm_alloc_pgd(struct mm_struct * mm)
401 mm->pgd = pgd_alloc(mm);
402 if (unlikely(!mm->pgd))
407 static inline void mm_free_pgd(struct mm_struct * mm)
409 pgd_free(mm, mm->pgd);
412 #define dup_mmap(mm, oldmm) (0)
413 #define mm_alloc_pgd(mm) (0)
414 #define mm_free_pgd(mm)
415 #endif /* CONFIG_MMU */
417 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
419 #define allocate_mm() (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
420 #define free_mm(mm) (kmem_cache_free(mm_cachep, (mm)))
422 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
424 static int __init coredump_filter_setup(char *s)
426 default_dump_filter =
427 (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
428 MMF_DUMP_FILTER_MASK;
432 __setup("coredump_filter=", coredump_filter_setup);
434 #include <linux/init_task.h>
436 static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
438 atomic_set(&mm->mm_users, 1);
439 atomic_set(&mm->mm_count, 1);
440 init_rwsem(&mm->mmap_sem);
441 INIT_LIST_HEAD(&mm->mmlist);
442 mm->flags = (current->mm) ?
443 (current->mm->flags & MMF_INIT_MASK) : default_dump_filter;
444 mm->core_state = NULL;
446 set_mm_counter(mm, file_rss, 0);
447 set_mm_counter(mm, anon_rss, 0);
448 spin_lock_init(&mm->page_table_lock);
449 spin_lock_init(&mm->ioctx_lock);
450 INIT_HLIST_HEAD(&mm->ioctx_list);
451 mm->free_area_cache = TASK_UNMAPPED_BASE;
452 mm->cached_hole_size = ~0UL;
453 mm_init_owner(mm, p);
455 if (likely(!mm_alloc_pgd(mm))) {
457 mmu_notifier_mm_init(mm);
466 * Allocate and initialize an mm_struct.
468 struct mm_struct * mm_alloc(void)
470 struct mm_struct * mm;
474 memset(mm, 0, sizeof(*mm));
475 mm = mm_init(mm, current);
481 * Called when the last reference to the mm
482 * is dropped: either by a lazy thread or by
483 * mmput. Free the page directory and the mm.
485 void __mmdrop(struct mm_struct *mm)
487 BUG_ON(mm == &init_mm);
490 mmu_notifier_mm_destroy(mm);
493 EXPORT_SYMBOL_GPL(__mmdrop);
496 * Decrement the use count and release all resources for an mm.
498 void mmput(struct mm_struct *mm)
502 if (atomic_dec_and_test(&mm->mm_users)) {
506 set_mm_exe_file(mm, NULL);
507 if (!list_empty(&mm->mmlist)) {
508 spin_lock(&mmlist_lock);
509 list_del(&mm->mmlist);
510 spin_unlock(&mmlist_lock);
516 EXPORT_SYMBOL_GPL(mmput);
519 * get_task_mm - acquire a reference to the task's mm
521 * Returns %NULL if the task has no mm. Checks PF_KTHREAD (meaning
522 * this kernel workthread has transiently adopted a user mm with use_mm,
523 * to do its AIO) is not set and if so returns a reference to it, after
524 * bumping up the use count. User must release the mm via mmput()
525 * after use. Typically used by /proc and ptrace.
527 struct mm_struct *get_task_mm(struct task_struct *task)
529 struct mm_struct *mm;
534 if (task->flags & PF_KTHREAD)
537 atomic_inc(&mm->mm_users);
542 EXPORT_SYMBOL_GPL(get_task_mm);
544 /* Please note the differences between mmput and mm_release.
545 * mmput is called whenever we stop holding onto a mm_struct,
546 * error success whatever.
548 * mm_release is called after a mm_struct has been removed
549 * from the current process.
551 * This difference is important for error handling, when we
552 * only half set up a mm_struct for a new process and need to restore
553 * the old one. Because we mmput the new mm_struct before
554 * restoring the old one. . .
555 * Eric Biederman 10 January 1998
557 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
559 struct completion *vfork_done = tsk->vfork_done;
561 /* Get rid of any futexes when releasing the mm */
563 if (unlikely(tsk->robust_list))
564 exit_robust_list(tsk);
566 if (unlikely(tsk->compat_robust_list))
567 compat_exit_robust_list(tsk);
571 /* Get rid of any cached register state */
572 deactivate_mm(tsk, mm);
574 /* notify parent sleeping on vfork() */
576 tsk->vfork_done = NULL;
577 complete(vfork_done);
581 * If we're exiting normally, clear a user-space tid field if
582 * requested. We leave this alone when dying by signal, to leave
583 * the value intact in a core dump, and to save the unnecessary
584 * trouble otherwise. Userland only wants this done for a sys_exit.
586 if (tsk->clear_child_tid) {
587 if (!(tsk->flags & PF_SIGNALED) &&
588 atomic_read(&mm->mm_users) > 1) {
590 * We don't check the error code - if userspace has
591 * not set up a proper pointer then tough luck.
593 put_user(0, tsk->clear_child_tid);
594 sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
597 tsk->clear_child_tid = NULL;
602 * Allocate a new mm structure and copy contents from the
603 * mm structure of the passed in task structure.
605 struct mm_struct *dup_mm(struct task_struct *tsk)
607 struct mm_struct *mm, *oldmm = current->mm;
617 memcpy(mm, oldmm, sizeof(*mm));
619 /* Initializing for Swap token stuff */
620 mm->token_priority = 0;
621 mm->last_interval = 0;
623 if (!mm_init(mm, tsk))
626 if (init_new_context(tsk, mm))
629 dup_mm_exe_file(oldmm, mm);
631 err = dup_mmap(mm, oldmm);
635 mm->hiwater_rss = get_mm_rss(mm);
636 mm->hiwater_vm = mm->total_vm;
648 * If init_new_context() failed, we cannot use mmput() to free the mm
649 * because it calls destroy_context()
656 static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
658 struct mm_struct * mm, *oldmm;
661 tsk->min_flt = tsk->maj_flt = 0;
662 tsk->nvcsw = tsk->nivcsw = 0;
663 #ifdef CONFIG_DETECT_HUNG_TASK
664 tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
668 tsk->active_mm = NULL;
671 * Are we cloning a kernel thread?
673 * We need to steal a active VM for that..
679 if (clone_flags & CLONE_VM) {
680 atomic_inc(&oldmm->mm_users);
691 /* Initializing for Swap token stuff */
692 mm->token_priority = 0;
693 mm->last_interval = 0;
703 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
705 struct fs_struct *fs = current->fs;
706 if (clone_flags & CLONE_FS) {
707 /* tsk->fs is already what we want */
708 write_lock(&fs->lock);
710 write_unlock(&fs->lock);
714 write_unlock(&fs->lock);
717 tsk->fs = copy_fs_struct(fs);
723 static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
725 struct files_struct *oldf, *newf;
729 * A background process may not have any files ...
731 oldf = current->files;
735 if (clone_flags & CLONE_FILES) {
736 atomic_inc(&oldf->count);
740 newf = dup_fd(oldf, &error);
750 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
753 struct io_context *ioc = current->io_context;
758 * Share io context with parent, if CLONE_IO is set
760 if (clone_flags & CLONE_IO) {
761 tsk->io_context = ioc_task_link(ioc);
762 if (unlikely(!tsk->io_context))
764 } else if (ioprio_valid(ioc->ioprio)) {
765 tsk->io_context = alloc_io_context(GFP_KERNEL, -1);
766 if (unlikely(!tsk->io_context))
769 tsk->io_context->ioprio = ioc->ioprio;
775 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
777 struct sighand_struct *sig;
779 if (clone_flags & CLONE_SIGHAND) {
780 atomic_inc(¤t->sighand->count);
783 sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
784 rcu_assign_pointer(tsk->sighand, sig);
787 atomic_set(&sig->count, 1);
788 memcpy(sig->action, current->sighand->action, sizeof(sig->action));
792 void __cleanup_sighand(struct sighand_struct *sighand)
794 if (atomic_dec_and_test(&sighand->count))
795 kmem_cache_free(sighand_cachep, sighand);
800 * Initialize POSIX timer handling for a thread group.
802 static void posix_cpu_timers_init_group(struct signal_struct *sig)
804 /* Thread group counters. */
805 thread_group_cputime_init(sig);
807 /* Expiration times and increments. */
808 sig->it_virt_expires = cputime_zero;
809 sig->it_virt_incr = cputime_zero;
810 sig->it_prof_expires = cputime_zero;
811 sig->it_prof_incr = cputime_zero;
813 /* Cached expiration times. */
814 sig->cputime_expires.prof_exp = cputime_zero;
815 sig->cputime_expires.virt_exp = cputime_zero;
816 sig->cputime_expires.sched_exp = 0;
818 if (sig->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY) {
819 sig->cputime_expires.prof_exp =
820 secs_to_cputime(sig->rlim[RLIMIT_CPU].rlim_cur);
821 sig->cputimer.running = 1;
824 /* The timer lists. */
825 INIT_LIST_HEAD(&sig->cpu_timers[0]);
826 INIT_LIST_HEAD(&sig->cpu_timers[1]);
827 INIT_LIST_HEAD(&sig->cpu_timers[2]);
830 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
832 struct signal_struct *sig;
834 if (clone_flags & CLONE_THREAD)
837 sig = kmem_cache_alloc(signal_cachep, GFP_KERNEL);
842 atomic_set(&sig->count, 1);
843 atomic_set(&sig->live, 1);
844 init_waitqueue_head(&sig->wait_chldexit);
846 if (clone_flags & CLONE_NEWPID)
847 sig->flags |= SIGNAL_UNKILLABLE;
848 sig->group_exit_code = 0;
849 sig->group_exit_task = NULL;
850 sig->group_stop_count = 0;
851 sig->curr_target = tsk;
852 init_sigpending(&sig->shared_pending);
853 INIT_LIST_HEAD(&sig->posix_timers);
855 hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
856 sig->it_real_incr.tv64 = 0;
857 sig->real_timer.function = it_real_fn;
859 sig->leader = 0; /* session leadership doesn't inherit */
860 sig->tty_old_pgrp = NULL;
863 sig->utime = sig->stime = sig->cutime = sig->cstime = cputime_zero;
864 sig->gtime = cputime_zero;
865 sig->cgtime = cputime_zero;
866 sig->nvcsw = sig->nivcsw = sig->cnvcsw = sig->cnivcsw = 0;
867 sig->min_flt = sig->maj_flt = sig->cmin_flt = sig->cmaj_flt = 0;
868 sig->inblock = sig->oublock = sig->cinblock = sig->coublock = 0;
869 task_io_accounting_init(&sig->ioac);
870 sig->sum_sched_runtime = 0;
871 taskstats_tgid_init(sig);
873 task_lock(current->group_leader);
874 memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
875 task_unlock(current->group_leader);
877 posix_cpu_timers_init_group(sig);
879 acct_init_pacct(&sig->pacct);
886 void __cleanup_signal(struct signal_struct *sig)
888 thread_group_cputime_free(sig);
889 tty_kref_put(sig->tty);
890 kmem_cache_free(signal_cachep, sig);
893 static void copy_flags(unsigned long clone_flags, struct task_struct *p)
895 unsigned long new_flags = p->flags;
897 new_flags &= ~PF_SUPERPRIV;
898 new_flags |= PF_FORKNOEXEC;
899 new_flags |= PF_STARTING;
900 p->flags = new_flags;
901 clear_freeze_flag(p);
904 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
906 current->clear_child_tid = tidptr;
908 return task_pid_vnr(current);
911 static void rt_mutex_init_task(struct task_struct *p)
913 spin_lock_init(&p->pi_lock);
914 #ifdef CONFIG_RT_MUTEXES
915 plist_head_init(&p->pi_waiters, &p->pi_lock);
916 p->pi_blocked_on = NULL;
920 #ifdef CONFIG_MM_OWNER
921 void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
925 #endif /* CONFIG_MM_OWNER */
928 * Initialize POSIX timer handling for a single task.
930 static void posix_cpu_timers_init(struct task_struct *tsk)
932 tsk->cputime_expires.prof_exp = cputime_zero;
933 tsk->cputime_expires.virt_exp = cputime_zero;
934 tsk->cputime_expires.sched_exp = 0;
935 INIT_LIST_HEAD(&tsk->cpu_timers[0]);
936 INIT_LIST_HEAD(&tsk->cpu_timers[1]);
937 INIT_LIST_HEAD(&tsk->cpu_timers[2]);
941 * This creates a new process as a copy of the old one,
942 * but does not actually start it yet.
944 * It copies the registers, and all the appropriate
945 * parts of the process environment (as per the clone
946 * flags). The actual kick-off is left to the caller.
948 static struct task_struct *copy_process(unsigned long clone_flags,
949 unsigned long stack_start,
950 struct pt_regs *regs,
951 unsigned long stack_size,
952 int __user *child_tidptr,
957 struct task_struct *p;
958 int cgroup_callbacks_done = 0;
960 if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
961 return ERR_PTR(-EINVAL);
964 * Thread groups must share signals as well, and detached threads
965 * can only be started up within the thread group.
967 if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
968 return ERR_PTR(-EINVAL);
971 * Shared signal handlers imply shared VM. By way of the above,
972 * thread groups also imply shared VM. Blocking this case allows
973 * for various simplifications in other code.
975 if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
976 return ERR_PTR(-EINVAL);
978 retval = security_task_create(clone_flags);
983 p = dup_task_struct(current);
987 ftrace_graph_init_task(p);
989 rt_mutex_init_task(p);
991 #ifdef CONFIG_PROVE_LOCKING
992 DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
993 DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
996 if (atomic_read(&p->real_cred->user->processes) >=
997 p->signal->rlim[RLIMIT_NPROC].rlim_cur) {
998 if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
999 p->real_cred->user != INIT_USER)
1003 retval = copy_creds(p, clone_flags);
1008 * If multiple threads are within copy_process(), then this check
1009 * triggers too late. This doesn't hurt, the check is only there
1010 * to stop root fork bombs.
1013 if (nr_threads >= max_threads)
1014 goto bad_fork_cleanup_count;
1016 if (!try_module_get(task_thread_info(p)->exec_domain->module))
1017 goto bad_fork_cleanup_count;
1019 if (p->binfmt && !try_module_get(p->binfmt->module))
1020 goto bad_fork_cleanup_put_domain;
1023 delayacct_tsk_init(p); /* Must remain after dup_task_struct() */
1024 copy_flags(clone_flags, p);
1025 INIT_LIST_HEAD(&p->children);
1026 INIT_LIST_HEAD(&p->sibling);
1027 rcu_copy_process(p);
1028 p->vfork_done = NULL;
1029 spin_lock_init(&p->alloc_lock);
1031 init_sigpending(&p->pending);
1033 p->utime = cputime_zero;
1034 p->stime = cputime_zero;
1035 p->gtime = cputime_zero;
1036 p->utimescaled = cputime_zero;
1037 p->stimescaled = cputime_zero;
1038 p->prev_utime = cputime_zero;
1039 p->prev_stime = cputime_zero;
1041 p->default_timer_slack_ns = current->timer_slack_ns;
1043 task_io_accounting_init(&p->ioac);
1044 acct_clear_integrals(p);
1046 posix_cpu_timers_init(p);
1048 p->lock_depth = -1; /* -1 = no lock */
1049 do_posix_clock_monotonic_gettime(&p->start_time);
1050 p->real_start_time = p->start_time;
1051 monotonic_to_bootbased(&p->real_start_time);
1052 p->io_context = NULL;
1053 p->audit_context = NULL;
1056 p->mempolicy = mpol_dup(p->mempolicy);
1057 if (IS_ERR(p->mempolicy)) {
1058 retval = PTR_ERR(p->mempolicy);
1059 p->mempolicy = NULL;
1060 goto bad_fork_cleanup_cgroup;
1062 mpol_fix_fork_child_flag(p);
1064 #ifdef CONFIG_TRACE_IRQFLAGS
1066 #ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
1067 p->hardirqs_enabled = 1;
1069 p->hardirqs_enabled = 0;
1071 p->hardirq_enable_ip = 0;
1072 p->hardirq_enable_event = 0;
1073 p->hardirq_disable_ip = _THIS_IP_;
1074 p->hardirq_disable_event = 0;
1075 p->softirqs_enabled = 1;
1076 p->softirq_enable_ip = _THIS_IP_;
1077 p->softirq_enable_event = 0;
1078 p->softirq_disable_ip = 0;
1079 p->softirq_disable_event = 0;
1080 p->hardirq_context = 0;
1081 p->softirq_context = 0;
1083 #ifdef CONFIG_LOCKDEP
1084 p->lockdep_depth = 0; /* no locks held yet */
1085 p->curr_chain_key = 0;
1086 p->lockdep_recursion = 0;
1089 #ifdef CONFIG_DEBUG_MUTEXES
1090 p->blocked_on = NULL; /* not blocked yet */
1095 /* Perform scheduler related setup. Assign this task to a CPU. */
1096 sched_fork(p, clone_flags);
1098 retval = perf_event_init_task(p);
1100 goto bad_fork_cleanup_policy;
1102 if ((retval = audit_alloc(p)))
1103 goto bad_fork_cleanup_policy;
1104 /* copy all the process information */
1105 if ((retval = copy_semundo(clone_flags, p)))
1106 goto bad_fork_cleanup_audit;
1107 if ((retval = copy_files(clone_flags, p)))
1108 goto bad_fork_cleanup_semundo;
1109 if ((retval = copy_fs(clone_flags, p)))
1110 goto bad_fork_cleanup_files;
1111 if ((retval = copy_sighand(clone_flags, p)))
1112 goto bad_fork_cleanup_fs;
1113 if ((retval = copy_signal(clone_flags, p)))
1114 goto bad_fork_cleanup_sighand;
1115 if ((retval = copy_mm(clone_flags, p)))
1116 goto bad_fork_cleanup_signal;
1117 if ((retval = copy_namespaces(clone_flags, p)))
1118 goto bad_fork_cleanup_mm;
1119 if ((retval = copy_io(clone_flags, p)))
1120 goto bad_fork_cleanup_namespaces;
1121 retval = copy_thread(clone_flags, stack_start, stack_size, p, regs);
1123 goto bad_fork_cleanup_io;
1125 if (pid != &init_struct_pid) {
1127 pid = alloc_pid(p->nsproxy->pid_ns);
1129 goto bad_fork_cleanup_io;
1131 if (clone_flags & CLONE_NEWPID) {
1132 retval = pid_ns_prepare_proc(p->nsproxy->pid_ns);
1134 goto bad_fork_free_pid;
1138 p->pid = pid_nr(pid);
1140 if (clone_flags & CLONE_THREAD)
1141 p->tgid = current->tgid;
1143 if (current->nsproxy != p->nsproxy) {
1144 retval = ns_cgroup_clone(p, pid);
1146 goto bad_fork_free_pid;
1149 p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1151 * Clear TID on mm_release()?
1153 p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr: NULL;
1155 p->robust_list = NULL;
1156 #ifdef CONFIG_COMPAT
1157 p->compat_robust_list = NULL;
1159 INIT_LIST_HEAD(&p->pi_state_list);
1160 p->pi_state_cache = NULL;
1163 * sigaltstack should be cleared when sharing the same VM
1165 if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1166 p->sas_ss_sp = p->sas_ss_size = 0;
1169 * Syscall tracing should be turned off in the child regardless
1172 clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1173 #ifdef TIF_SYSCALL_EMU
1174 clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1176 clear_all_latency_tracing(p);
1178 /* ok, now we should be set up.. */
1179 p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
1180 p->pdeath_signal = 0;
1184 * Ok, make it visible to the rest of the system.
1185 * We dont wake it up yet.
1187 p->group_leader = p;
1188 INIT_LIST_HEAD(&p->thread_group);
1190 /* Now that the task is set up, run cgroup callbacks if
1191 * necessary. We need to run them before the task is visible
1192 * on the tasklist. */
1193 cgroup_fork_callbacks(p);
1194 cgroup_callbacks_done = 1;
1196 /* Need tasklist lock for parent etc handling! */
1197 write_lock_irq(&tasklist_lock);
1200 * The task hasn't been attached yet, so its cpus_allowed mask will
1201 * not be changed, nor will its assigned CPU.
1203 * The cpus_allowed mask of the parent may have changed after it was
1204 * copied first time - so re-copy it here, then check the child's CPU
1205 * to ensure it is on a valid CPU (and if not, just force it back to
1206 * parent's CPU). This avoids alot of nasty races.
1208 p->cpus_allowed = current->cpus_allowed;
1209 p->rt.nr_cpus_allowed = current->rt.nr_cpus_allowed;
1210 if (unlikely(!cpu_isset(task_cpu(p), p->cpus_allowed) ||
1211 !cpu_online(task_cpu(p))))
1212 set_task_cpu(p, smp_processor_id());
1214 /* CLONE_PARENT re-uses the old parent */
1215 if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1216 p->real_parent = current->real_parent;
1217 p->parent_exec_id = current->parent_exec_id;
1219 p->real_parent = current;
1220 p->parent_exec_id = current->self_exec_id;
1223 spin_lock(¤t->sighand->siglock);
1226 * Process group and session signals need to be delivered to just the
1227 * parent before the fork or both the parent and the child after the
1228 * fork. Restart if a signal comes in before we add the new process to
1229 * it's process group.
1230 * A fatal signal pending means that current will exit, so the new
1231 * thread can't slip out of an OOM kill (or normal SIGKILL).
1233 recalc_sigpending();
1234 if (signal_pending(current)) {
1235 spin_unlock(¤t->sighand->siglock);
1236 write_unlock_irq(&tasklist_lock);
1237 retval = -ERESTARTNOINTR;
1238 goto bad_fork_free_pid;
1241 if (clone_flags & CLONE_THREAD) {
1242 atomic_inc(¤t->signal->count);
1243 atomic_inc(¤t->signal->live);
1244 p->group_leader = current->group_leader;
1245 list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);
1248 if (likely(p->pid)) {
1249 list_add_tail(&p->sibling, &p->real_parent->children);
1250 tracehook_finish_clone(p, clone_flags, trace);
1252 if (thread_group_leader(p)) {
1253 if (clone_flags & CLONE_NEWPID)
1254 p->nsproxy->pid_ns->child_reaper = p;
1256 p->signal->leader_pid = pid;
1257 tty_kref_put(p->signal->tty);
1258 p->signal->tty = tty_kref_get(current->signal->tty);
1259 attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
1260 attach_pid(p, PIDTYPE_SID, task_session(current));
1261 list_add_tail_rcu(&p->tasks, &init_task.tasks);
1262 __get_cpu_var(process_counts)++;
1264 attach_pid(p, PIDTYPE_PID, pid);
1269 spin_unlock(¤t->sighand->siglock);
1270 write_unlock_irq(&tasklist_lock);
1271 proc_fork_connector(p);
1272 cgroup_post_fork(p);
1277 if (pid != &init_struct_pid)
1279 bad_fork_cleanup_io:
1280 put_io_context(p->io_context);
1281 bad_fork_cleanup_namespaces:
1282 exit_task_namespaces(p);
1283 bad_fork_cleanup_mm:
1286 bad_fork_cleanup_signal:
1287 if (!(clone_flags & CLONE_THREAD))
1288 __cleanup_signal(p->signal);
1289 bad_fork_cleanup_sighand:
1290 __cleanup_sighand(p->sighand);
1291 bad_fork_cleanup_fs:
1292 exit_fs(p); /* blocking */
1293 bad_fork_cleanup_files:
1294 exit_files(p); /* blocking */
1295 bad_fork_cleanup_semundo:
1297 bad_fork_cleanup_audit:
1299 bad_fork_cleanup_policy:
1300 perf_event_free_task(p);
1302 mpol_put(p->mempolicy);
1303 bad_fork_cleanup_cgroup:
1305 cgroup_exit(p, cgroup_callbacks_done);
1306 delayacct_tsk_free(p);
1308 module_put(p->binfmt->module);
1309 bad_fork_cleanup_put_domain:
1310 module_put(task_thread_info(p)->exec_domain->module);
1311 bad_fork_cleanup_count:
1312 atomic_dec(&p->cred->user->processes);
1317 return ERR_PTR(retval);
1320 noinline struct pt_regs * __cpuinit __attribute__((weak)) idle_regs(struct pt_regs *regs)
1322 memset(regs, 0, sizeof(struct pt_regs));
1326 struct task_struct * __cpuinit fork_idle(int cpu)
1328 struct task_struct *task;
1329 struct pt_regs regs;
1331 task = copy_process(CLONE_VM, 0, idle_regs(®s), 0, NULL,
1332 &init_struct_pid, 0);
1334 init_idle(task, cpu);
1340 * Ok, this is the main fork-routine.
1342 * It copies the process, and if successful kick-starts
1343 * it and waits for it to finish using the VM if required.
1345 long do_fork(unsigned long clone_flags,
1346 unsigned long stack_start,
1347 struct pt_regs *regs,
1348 unsigned long stack_size,
1349 int __user *parent_tidptr,
1350 int __user *child_tidptr)
1352 struct task_struct *p;
1357 * Do some preliminary argument and permissions checking before we
1358 * actually start allocating stuff
1360 if (clone_flags & CLONE_NEWUSER) {
1361 if (clone_flags & CLONE_THREAD)
1363 /* hopefully this check will go away when userns support is
1366 if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SETUID) ||
1367 !capable(CAP_SETGID))
1372 * We hope to recycle these flags after 2.6.26
1374 if (unlikely(clone_flags & CLONE_STOPPED)) {
1375 static int __read_mostly count = 100;
1377 if (count > 0 && printk_ratelimit()) {
1378 char comm[TASK_COMM_LEN];
1381 printk(KERN_INFO "fork(): process `%s' used deprecated "
1382 "clone flags 0x%lx\n",
1383 get_task_comm(comm, current),
1384 clone_flags & CLONE_STOPPED);
1389 * When called from kernel_thread, don't do user tracing stuff.
1391 if (likely(user_mode(regs)))
1392 trace = tracehook_prepare_clone(clone_flags);
1394 p = copy_process(clone_flags, stack_start, regs, stack_size,
1395 child_tidptr, NULL, trace);
1397 * Do this prior waking up the new thread - the thread pointer
1398 * might get invalid after that point, if the thread exits quickly.
1401 struct completion vfork;
1403 trace_sched_process_fork(current, p);
1405 nr = task_pid_vnr(p);
1407 if (clone_flags & CLONE_PARENT_SETTID)
1408 put_user(nr, parent_tidptr);
1410 if (clone_flags & CLONE_VFORK) {
1411 p->vfork_done = &vfork;
1412 init_completion(&vfork);
1415 audit_finish_fork(p);
1416 tracehook_report_clone(regs, clone_flags, nr, p);
1419 * We set PF_STARTING at creation in case tracing wants to
1420 * use this to distinguish a fully live task from one that
1421 * hasn't gotten to tracehook_report_clone() yet. Now we
1422 * clear it and set the child going.
1424 p->flags &= ~PF_STARTING;
1426 if (unlikely(clone_flags & CLONE_STOPPED)) {
1428 * We'll start up with an immediate SIGSTOP.
1430 sigaddset(&p->pending.signal, SIGSTOP);
1431 set_tsk_thread_flag(p, TIF_SIGPENDING);
1432 __set_task_state(p, TASK_STOPPED);
1434 wake_up_new_task(p, clone_flags);
1437 tracehook_report_clone_complete(trace, regs,
1438 clone_flags, nr, p);
1440 if (clone_flags & CLONE_VFORK) {
1441 freezer_do_not_count();
1442 wait_for_completion(&vfork);
1444 tracehook_report_vfork_done(p, nr);
1452 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1453 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1456 static void sighand_ctor(void *data)
1458 struct sighand_struct *sighand = data;
1460 spin_lock_init(&sighand->siglock);
1461 init_waitqueue_head(&sighand->signalfd_wqh);
1464 void __init proc_caches_init(void)
1466 sighand_cachep = kmem_cache_create("sighand_cache",
1467 sizeof(struct sighand_struct), 0,
1468 SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1469 SLAB_NOTRACK, sighand_ctor);
1470 signal_cachep = kmem_cache_create("signal_cache",
1471 sizeof(struct signal_struct), 0,
1472 SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1473 files_cachep = kmem_cache_create("files_cache",
1474 sizeof(struct files_struct), 0,
1475 SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1476 fs_cachep = kmem_cache_create("fs_cache",
1477 sizeof(struct fs_struct), 0,
1478 SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1479 mm_cachep = kmem_cache_create("mm_struct",
1480 sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1481 SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1482 vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1487 * Check constraints on flags passed to the unshare system call and
1488 * force unsharing of additional process context as appropriate.
1490 static void check_unshare_flags(unsigned long *flags_ptr)
1493 * If unsharing a thread from a thread group, must also
1496 if (*flags_ptr & CLONE_THREAD)
1497 *flags_ptr |= CLONE_VM;
1500 * If unsharing vm, must also unshare signal handlers.
1502 if (*flags_ptr & CLONE_VM)
1503 *flags_ptr |= CLONE_SIGHAND;
1506 * If unsharing signal handlers and the task was created
1507 * using CLONE_THREAD, then must unshare the thread
1509 if ((*flags_ptr & CLONE_SIGHAND) &&
1510 (atomic_read(¤t->signal->count) > 1))
1511 *flags_ptr |= CLONE_THREAD;
1514 * If unsharing namespace, must also unshare filesystem information.
1516 if (*flags_ptr & CLONE_NEWNS)
1517 *flags_ptr |= CLONE_FS;
1521 * Unsharing of tasks created with CLONE_THREAD is not supported yet
1523 static int unshare_thread(unsigned long unshare_flags)
1525 if (unshare_flags & CLONE_THREAD)
1532 * Unshare the filesystem structure if it is being shared
1534 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1536 struct fs_struct *fs = current->fs;
1538 if (!(unshare_flags & CLONE_FS) || !fs)
1541 /* don't need lock here; in the worst case we'll do useless copy */
1545 *new_fsp = copy_fs_struct(fs);
1553 * Unsharing of sighand is not supported yet
1555 static int unshare_sighand(unsigned long unshare_flags, struct sighand_struct **new_sighp)
1557 struct sighand_struct *sigh = current->sighand;
1559 if ((unshare_flags & CLONE_SIGHAND) && atomic_read(&sigh->count) > 1)
1566 * Unshare vm if it is being shared
1568 static int unshare_vm(unsigned long unshare_flags, struct mm_struct **new_mmp)
1570 struct mm_struct *mm = current->mm;
1572 if ((unshare_flags & CLONE_VM) &&
1573 (mm && atomic_read(&mm->mm_users) > 1)) {
1581 * Unshare file descriptor table if it is being shared
1583 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1585 struct files_struct *fd = current->files;
1588 if ((unshare_flags & CLONE_FILES) &&
1589 (fd && atomic_read(&fd->count) > 1)) {
1590 *new_fdp = dup_fd(fd, &error);
1599 * unshare allows a process to 'unshare' part of the process
1600 * context which was originally shared using clone. copy_*
1601 * functions used by do_fork() cannot be used here directly
1602 * because they modify an inactive task_struct that is being
1603 * constructed. Here we are modifying the current, active,
1606 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1609 struct fs_struct *fs, *new_fs = NULL;
1610 struct sighand_struct *new_sigh = NULL;
1611 struct mm_struct *mm, *new_mm = NULL, *active_mm = NULL;
1612 struct files_struct *fd, *new_fd = NULL;
1613 struct nsproxy *new_nsproxy = NULL;
1616 check_unshare_flags(&unshare_flags);
1618 /* Return -EINVAL for all unsupported flags */
1620 if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1621 CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1622 CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET))
1623 goto bad_unshare_out;
1626 * CLONE_NEWIPC must also detach from the undolist: after switching
1627 * to a new ipc namespace, the semaphore arrays from the old
1628 * namespace are unreachable.
1630 if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1632 if ((err = unshare_thread(unshare_flags)))
1633 goto bad_unshare_out;
1634 if ((err = unshare_fs(unshare_flags, &new_fs)))
1635 goto bad_unshare_cleanup_thread;
1636 if ((err = unshare_sighand(unshare_flags, &new_sigh)))
1637 goto bad_unshare_cleanup_fs;
1638 if ((err = unshare_vm(unshare_flags, &new_mm)))
1639 goto bad_unshare_cleanup_sigh;
1640 if ((err = unshare_fd(unshare_flags, &new_fd)))
1641 goto bad_unshare_cleanup_vm;
1642 if ((err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
1644 goto bad_unshare_cleanup_fd;
1646 if (new_fs || new_mm || new_fd || do_sysvsem || new_nsproxy) {
1649 * CLONE_SYSVSEM is equivalent to sys_exit().
1655 switch_task_namespaces(current, new_nsproxy);
1663 write_lock(&fs->lock);
1664 current->fs = new_fs;
1669 write_unlock(&fs->lock);
1674 active_mm = current->active_mm;
1675 current->mm = new_mm;
1676 current->active_mm = new_mm;
1677 activate_mm(active_mm, new_mm);
1682 fd = current->files;
1683 current->files = new_fd;
1687 task_unlock(current);
1691 put_nsproxy(new_nsproxy);
1693 bad_unshare_cleanup_fd:
1695 put_files_struct(new_fd);
1697 bad_unshare_cleanup_vm:
1701 bad_unshare_cleanup_sigh:
1703 if (atomic_dec_and_test(&new_sigh->count))
1704 kmem_cache_free(sighand_cachep, new_sigh);
1706 bad_unshare_cleanup_fs:
1708 free_fs_struct(new_fs);
1710 bad_unshare_cleanup_thread:
1716 * Helper to unshare the files of the current task.
1717 * We don't want to expose copy_files internals to
1718 * the exec layer of the kernel.
1721 int unshare_files(struct files_struct **displaced)
1723 struct task_struct *task = current;
1724 struct files_struct *copy = NULL;
1727 error = unshare_fd(CLONE_FILES, ©);
1728 if (error || !copy) {
1732 *displaced = task->files;