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Linux/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 #include <linux/sysctl.h>
 78 #include <linux/kcov.h>
 79 
 80 #include <asm/pgtable.h>
 81 #include <asm/pgalloc.h>
 82 #include <asm/uaccess.h>
 83 #include <asm/mmu_context.h>
 84 #include <asm/cacheflush.h>
 85 #include <asm/tlbflush.h>
 86 
 87 #include <trace/events/sched.h>
 88 
 89 #define CREATE_TRACE_POINTS
 90 #include <trace/events/task.h>
 91 
 92 /*
 93  * Minimum number of threads to boot the kernel
 94  */
 95 #define MIN_THREADS 20
 96 
 97 /*
 98  * Maximum number of threads
 99  */
100 #define MAX_THREADS FUTEX_TID_MASK
101 
102 /*
103  * Protected counters by write_lock_irq(&tasklist_lock)
104  */
105 unsigned long total_forks;      /* Handle normal Linux uptimes. */
106 int nr_threads;                 /* The idle threads do not count.. */
107 
108 int max_threads;                /* tunable limit on nr_threads */
109 
110 DEFINE_PER_CPU(unsigned long, process_counts) = 0;
111 
112 __cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
113 
114 #ifdef CONFIG_PROVE_RCU
115 int lockdep_tasklist_lock_is_held(void)
116 {
117         return lockdep_is_held(&tasklist_lock);
118 }
119 EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
120 #endif /* #ifdef CONFIG_PROVE_RCU */
121 
122 int nr_processes(void)
123 {
124         int cpu;
125         int total = 0;
126 
127         for_each_possible_cpu(cpu)
128                 total += per_cpu(process_counts, cpu);
129 
130         return total;
131 }
132 
133 void __weak arch_release_task_struct(struct task_struct *tsk)
134 {
135 }
136 
137 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
138 static struct kmem_cache *task_struct_cachep;
139 
140 static inline struct task_struct *alloc_task_struct_node(int node)
141 {
142         return kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL, node);
143 }
144 
145 static inline void free_task_struct(struct task_struct *tsk)
146 {
147         kmem_cache_free(task_struct_cachep, tsk);
148 }
149 #endif
150 
151 void __weak arch_release_thread_stack(unsigned long *stack)
152 {
153 }
154 
155 #ifndef CONFIG_ARCH_THREAD_STACK_ALLOCATOR
156 
157 /*
158  * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
159  * kmemcache based allocator.
160  */
161 # if THREAD_SIZE >= PAGE_SIZE
162 static unsigned long *alloc_thread_stack_node(struct task_struct *tsk,
163                                                   int node)
164 {
165         struct page *page = alloc_kmem_pages_node(node, THREADINFO_GFP,
166                                                   THREAD_SIZE_ORDER);
167 
168         if (page)
169                 memcg_kmem_update_page_stat(page, MEMCG_KERNEL_STACK,
170                                             1 << THREAD_SIZE_ORDER);
171 
172         return page ? page_address(page) : NULL;
173 }
174 
175 static inline void free_thread_stack(unsigned long *stack)
176 {
177         struct page *page = virt_to_page(stack);
178 
179         memcg_kmem_update_page_stat(page, MEMCG_KERNEL_STACK,
180                                     -(1 << THREAD_SIZE_ORDER));
181         __free_kmem_pages(page, THREAD_SIZE_ORDER);
182 }
183 # else
184 static struct kmem_cache *thread_stack_cache;
185 
186 static unsigned long *alloc_thread_stack_node(struct task_struct *tsk,
187                                                   int node)
188 {
189         return kmem_cache_alloc_node(thread_stack_cache, THREADINFO_GFP, node);
190 }
191 
192 static void free_thread_stack(unsigned long *stack)
193 {
194         kmem_cache_free(thread_stack_cache, stack);
195 }
196 
197 void thread_stack_cache_init(void)
198 {
199         thread_stack_cache = kmem_cache_create("thread_stack", THREAD_SIZE,
200                                               THREAD_SIZE, 0, NULL);
201         BUG_ON(thread_stack_cache == NULL);
202 }
203 # endif
204 #endif
205 
206 /* SLAB cache for signal_struct structures (tsk->signal) */
207 static struct kmem_cache *signal_cachep;
208 
209 /* SLAB cache for sighand_struct structures (tsk->sighand) */
210 struct kmem_cache *sighand_cachep;
211 
212 /* SLAB cache for files_struct structures (tsk->files) */
213 struct kmem_cache *files_cachep;
214 
215 /* SLAB cache for fs_struct structures (tsk->fs) */
216 struct kmem_cache *fs_cachep;
217 
218 /* SLAB cache for vm_area_struct structures */
219 struct kmem_cache *vm_area_cachep;
220 
221 /* SLAB cache for mm_struct structures (tsk->mm) */
222 static struct kmem_cache *mm_cachep;
223 
224 static void account_kernel_stack(unsigned long *stack, int account)
225 {
226         struct zone *zone = page_zone(virt_to_page(stack));
227 
228         mod_zone_page_state(zone, NR_KERNEL_STACK, account);
229 }
230 
231 void free_task(struct task_struct *tsk)
232 {
233         account_kernel_stack(tsk->stack, -1);
234         arch_release_thread_stack(tsk->stack);
235         free_thread_stack(tsk->stack);
236         rt_mutex_debug_task_free(tsk);
237         ftrace_graph_exit_task(tsk);
238         put_seccomp_filter(tsk);
239         arch_release_task_struct(tsk);
240         free_task_struct(tsk);
241 }
242 EXPORT_SYMBOL(free_task);
243 
244 static inline void free_signal_struct(struct signal_struct *sig)
245 {
246         taskstats_tgid_free(sig);
247         sched_autogroup_exit(sig);
248         kmem_cache_free(signal_cachep, sig);
249 }
250 
251 static inline void put_signal_struct(struct signal_struct *sig)
252 {
253         if (atomic_dec_and_test(&sig->sigcnt))
254                 free_signal_struct(sig);
255 }
256 
257 void __put_task_struct(struct task_struct *tsk)
258 {
259         WARN_ON(!tsk->exit_state);
260         WARN_ON(atomic_read(&tsk->usage));
261         WARN_ON(tsk == current);
262 
263         cgroup_free(tsk);
264         task_numa_free(tsk);
265         security_task_free(tsk);
266         exit_creds(tsk);
267         delayacct_tsk_free(tsk);
268         put_signal_struct(tsk->signal);
269 
270         if (!profile_handoff_task(tsk))
271                 free_task(tsk);
272 }
273 EXPORT_SYMBOL_GPL(__put_task_struct);
274 
275 void __init __weak arch_task_cache_init(void) { }
276 
277 /*
278  * set_max_threads
279  */
280 static void set_max_threads(unsigned int max_threads_suggested)
281 {
282         u64 threads;
283 
284         /*
285          * The number of threads shall be limited such that the thread
286          * structures may only consume a small part of the available memory.
287          */
288         if (fls64(totalram_pages) + fls64(PAGE_SIZE) > 64)
289                 threads = MAX_THREADS;
290         else
291                 threads = div64_u64((u64) totalram_pages * (u64) PAGE_SIZE,
292                                     (u64) THREAD_SIZE * 8UL);
293 
294         if (threads > max_threads_suggested)
295                 threads = max_threads_suggested;
296 
297         max_threads = clamp_t(u64, threads, MIN_THREADS, MAX_THREADS);
298 }
299 
300 #ifdef CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT
301 /* Initialized by the architecture: */
302 int arch_task_struct_size __read_mostly;
303 #endif
304 
305 void __init fork_init(void)
306 {
307 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
308 #ifndef ARCH_MIN_TASKALIGN
309 #define ARCH_MIN_TASKALIGN      L1_CACHE_BYTES
310 #endif
311         /* create a slab on which task_structs can be allocated */
312         task_struct_cachep = kmem_cache_create("task_struct",
313                         arch_task_struct_size, ARCH_MIN_TASKALIGN,
314                         SLAB_PANIC|SLAB_NOTRACK|SLAB_ACCOUNT, NULL);
315 #endif
316 
317         /* do the arch specific task caches init */
318         arch_task_cache_init();
319 
320         set_max_threads(MAX_THREADS);
321 
322         init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
323         init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
324         init_task.signal->rlim[RLIMIT_SIGPENDING] =
325                 init_task.signal->rlim[RLIMIT_NPROC];
326 }
327 
328 int __weak arch_dup_task_struct(struct task_struct *dst,
329                                                struct task_struct *src)
330 {
331         *dst = *src;
332         return 0;
333 }
334 
335 void set_task_stack_end_magic(struct task_struct *tsk)
336 {
337         unsigned long *stackend;
338 
339         stackend = end_of_stack(tsk);
340         *stackend = STACK_END_MAGIC;    /* for overflow detection */
341 }
342 
343 static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
344 {
345         struct task_struct *tsk;
346         unsigned long *stack;
347         int err;
348 
349         if (node == NUMA_NO_NODE)
350                 node = tsk_fork_get_node(orig);
351         tsk = alloc_task_struct_node(node);
352         if (!tsk)
353                 return NULL;
354 
355         stack = alloc_thread_stack_node(tsk, node);
356         if (!stack)
357                 goto free_tsk;
358 
359         err = arch_dup_task_struct(tsk, orig);
360         if (err)
361                 goto free_stack;
362 
363         tsk->stack = stack;
364 #ifdef CONFIG_SECCOMP
365         /*
366          * We must handle setting up seccomp filters once we're under
367          * the sighand lock in case orig has changed between now and
368          * then. Until then, filter must be NULL to avoid messing up
369          * the usage counts on the error path calling free_task.
370          */
371         tsk->seccomp.filter = NULL;
372 #endif
373 
374         setup_thread_stack(tsk, orig);
375         clear_user_return_notifier(tsk);
376         clear_tsk_need_resched(tsk);
377         set_task_stack_end_magic(tsk);
378 
379 #ifdef CONFIG_CC_STACKPROTECTOR
380         tsk->stack_canary = get_random_int();
381 #endif
382 
383         /*
384          * One for us, one for whoever does the "release_task()" (usually
385          * parent)
386          */
387         atomic_set(&tsk->usage, 2);
388 #ifdef CONFIG_BLK_DEV_IO_TRACE
389         tsk->btrace_seq = 0;
390 #endif
391         tsk->splice_pipe = NULL;
392         tsk->task_frag.page = NULL;
393         tsk->wake_q.next = NULL;
394 
395         account_kernel_stack(stack, 1);
396 
397         kcov_task_init(tsk);
398 
399         return tsk;
400 
401 free_stack:
402         free_thread_stack(stack);
403 free_tsk:
404         free_task_struct(tsk);
405         return NULL;
406 }
407 
408 #ifdef CONFIG_MMU
409 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
410 {
411         struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
412         struct rb_node **rb_link, *rb_parent;
413         int retval;
414         unsigned long charge;
415 
416         uprobe_start_dup_mmap();
417         if (down_write_killable(&oldmm->mmap_sem)) {
418                 retval = -EINTR;
419                 goto fail_uprobe_end;
420         }
421         flush_cache_dup_mm(oldmm);
422         uprobe_dup_mmap(oldmm, mm);
423         /*
424          * Not linked in yet - no deadlock potential:
425          */
426         down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
427 
428         /* No ordering required: file already has been exposed. */
429         RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
430 
431         mm->total_vm = oldmm->total_vm;
432         mm->data_vm = oldmm->data_vm;
433         mm->exec_vm = oldmm->exec_vm;
434         mm->stack_vm = oldmm->stack_vm;
435 
436         rb_link = &mm->mm_rb.rb_node;
437         rb_parent = NULL;
438         pprev = &mm->mmap;
439         retval = ksm_fork(mm, oldmm);
440         if (retval)
441                 goto out;
442         retval = khugepaged_fork(mm, oldmm);
443         if (retval)
444                 goto out;
445 
446         prev = NULL;
447         for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
448                 struct file *file;
449 
450                 if (mpnt->vm_flags & VM_DONTCOPY) {
451                         vm_stat_account(mm, mpnt->vm_flags, -vma_pages(mpnt));
452                         continue;
453                 }
454                 charge = 0;
455                 if (mpnt->vm_flags & VM_ACCOUNT) {
456                         unsigned long len = vma_pages(mpnt);
457 
458                         if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
459                                 goto fail_nomem;
460                         charge = len;
461                 }
462                 tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
463                 if (!tmp)
464                         goto fail_nomem;
465                 *tmp = *mpnt;
466                 INIT_LIST_HEAD(&tmp->anon_vma_chain);
467                 retval = vma_dup_policy(mpnt, tmp);
468                 if (retval)
469                         goto fail_nomem_policy;
470                 tmp->vm_mm = mm;
471                 if (anon_vma_fork(tmp, mpnt))
472                         goto fail_nomem_anon_vma_fork;
473                 tmp->vm_flags &=
474                         ~(VM_LOCKED|VM_LOCKONFAULT|VM_UFFD_MISSING|VM_UFFD_WP);
475                 tmp->vm_next = tmp->vm_prev = NULL;
476                 tmp->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
477                 file = tmp->vm_file;
478                 if (file) {
479                         struct inode *inode = file_inode(file);
480                         struct address_space *mapping = file->f_mapping;
481 
482                         get_file(file);
483                         if (tmp->vm_flags & VM_DENYWRITE)
484                                 atomic_dec(&inode->i_writecount);
485                         i_mmap_lock_write(mapping);
486                         if (tmp->vm_flags & VM_SHARED)
487                                 atomic_inc(&mapping->i_mmap_writable);
488                         flush_dcache_mmap_lock(mapping);
489                         /* insert tmp into the share list, just after mpnt */
490                         vma_interval_tree_insert_after(tmp, mpnt,
491                                         &mapping->i_mmap);
492                         flush_dcache_mmap_unlock(mapping);
493                         i_mmap_unlock_write(mapping);
494                 }
495 
496                 /*
497                  * Clear hugetlb-related page reserves for children. This only
498                  * affects MAP_PRIVATE mappings. Faults generated by the child
499                  * are not guaranteed to succeed, even if read-only
500                  */
501                 if (is_vm_hugetlb_page(tmp))
502                         reset_vma_resv_huge_pages(tmp);
503 
504                 /*
505                  * Link in the new vma and copy the page table entries.
506                  */
507                 *pprev = tmp;
508                 pprev = &tmp->vm_next;
509                 tmp->vm_prev = prev;
510                 prev = tmp;
511 
512                 __vma_link_rb(mm, tmp, rb_link, rb_parent);
513                 rb_link = &tmp->vm_rb.rb_right;
514                 rb_parent = &tmp->vm_rb;
515 
516                 mm->map_count++;
517                 retval = copy_page_range(mm, oldmm, mpnt);
518 
519                 if (tmp->vm_ops && tmp->vm_ops->open)
520                         tmp->vm_ops->open(tmp);
521 
522                 if (retval)
523                         goto out;
524         }
525         /* a new mm has just been created */
526         arch_dup_mmap(oldmm, mm);
527         retval = 0;
528 out:
529         up_write(&mm->mmap_sem);
530         flush_tlb_mm(oldmm);
531         up_write(&oldmm->mmap_sem);
532 fail_uprobe_end:
533         uprobe_end_dup_mmap();
534         return retval;
535 fail_nomem_anon_vma_fork:
536         mpol_put(vma_policy(tmp));
537 fail_nomem_policy:
538         kmem_cache_free(vm_area_cachep, tmp);
539 fail_nomem:
540         retval = -ENOMEM;
541         vm_unacct_memory(charge);
542         goto out;
543 }
544 
545 static inline int mm_alloc_pgd(struct mm_struct *mm)
546 {
547         mm->pgd = pgd_alloc(mm);
548         if (unlikely(!mm->pgd))
549                 return -ENOMEM;
550         return 0;
551 }
552 
553 static inline void mm_free_pgd(struct mm_struct *mm)
554 {
555         pgd_free(mm, mm->pgd);
556 }
557 #else
558 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
559 {
560         down_write(&oldmm->mmap_sem);
561         RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
562         up_write(&oldmm->mmap_sem);
563         return 0;
564 }
565 #define mm_alloc_pgd(mm)        (0)
566 #define mm_free_pgd(mm)
567 #endif /* CONFIG_MMU */
568 
569 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
570 
571 #define allocate_mm()   (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
572 #define free_mm(mm)     (kmem_cache_free(mm_cachep, (mm)))
573 
574 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
575 
576 static int __init coredump_filter_setup(char *s)
577 {
578         default_dump_filter =
579                 (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
580                 MMF_DUMP_FILTER_MASK;
581         return 1;
582 }
583 
584 __setup("coredump_filter=", coredump_filter_setup);
585 
586 #include <linux/init_task.h>
587 
588 static void mm_init_aio(struct mm_struct *mm)
589 {
590 #ifdef CONFIG_AIO
591         spin_lock_init(&mm->ioctx_lock);
592         mm->ioctx_table = NULL;
593 #endif
594 }
595 
596 static void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
597 {
598 #ifdef CONFIG_MEMCG
599         mm->owner = p;
600 #endif
601 }
602 
603 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
604 {
605         mm->mmap = NULL;
606         mm->mm_rb = RB_ROOT;
607         mm->vmacache_seqnum = 0;
608         atomic_set(&mm->mm_users, 1);
609         atomic_set(&mm->mm_count, 1);
610         init_rwsem(&mm->mmap_sem);
611         INIT_LIST_HEAD(&mm->mmlist);
612         mm->core_state = NULL;
613         atomic_long_set(&mm->nr_ptes, 0);
614         mm_nr_pmds_init(mm);
615         mm->map_count = 0;
616         mm->locked_vm = 0;
617         mm->pinned_vm = 0;
618         memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
619         spin_lock_init(&mm->page_table_lock);
620         mm_init_cpumask(mm);
621         mm_init_aio(mm);
622         mm_init_owner(mm, p);
623         mmu_notifier_mm_init(mm);
624         clear_tlb_flush_pending(mm);
625 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
626         mm->pmd_huge_pte = NULL;
627 #endif
628 
629         if (current->mm) {
630                 mm->flags = current->mm->flags & MMF_INIT_MASK;
631                 mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
632         } else {
633                 mm->flags = default_dump_filter;
634                 mm->def_flags = 0;
635         }
636 
637         if (mm_alloc_pgd(mm))
638                 goto fail_nopgd;
639 
640         if (init_new_context(p, mm))
641                 goto fail_nocontext;
642 
643         return mm;
644 
645 fail_nocontext:
646         mm_free_pgd(mm);
647 fail_nopgd:
648         free_mm(mm);
649         return NULL;
650 }
651 
652 static void check_mm(struct mm_struct *mm)
653 {
654         int i;
655 
656         for (i = 0; i < NR_MM_COUNTERS; i++) {
657                 long x = atomic_long_read(&mm->rss_stat.count[i]);
658 
659                 if (unlikely(x))
660                         printk(KERN_ALERT "BUG: Bad rss-counter state "
661                                           "mm:%p idx:%d val:%ld\n", mm, i, x);
662         }
663 
664         if (atomic_long_read(&mm->nr_ptes))
665                 pr_alert("BUG: non-zero nr_ptes on freeing mm: %ld\n",
666                                 atomic_long_read(&mm->nr_ptes));
667         if (mm_nr_pmds(mm))
668                 pr_alert("BUG: non-zero nr_pmds on freeing mm: %ld\n",
669                                 mm_nr_pmds(mm));
670 
671 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
672         VM_BUG_ON_MM(mm->pmd_huge_pte, mm);
673 #endif
674 }
675 
676 /*
677  * Allocate and initialize an mm_struct.
678  */
679 struct mm_struct *mm_alloc(void)
680 {
681         struct mm_struct *mm;
682 
683         mm = allocate_mm();
684         if (!mm)
685                 return NULL;
686 
687         memset(mm, 0, sizeof(*mm));
688         return mm_init(mm, current);
689 }
690 
691 /*
692  * Called when the last reference to the mm
693  * is dropped: either by a lazy thread or by
694  * mmput. Free the page directory and the mm.
695  */
696 void __mmdrop(struct mm_struct *mm)
697 {
698         BUG_ON(mm == &init_mm);
699         mm_free_pgd(mm);
700         destroy_context(mm);
701         mmu_notifier_mm_destroy(mm);
702         check_mm(mm);
703         free_mm(mm);
704 }
705 EXPORT_SYMBOL_GPL(__mmdrop);
706 
707 static inline void __mmput(struct mm_struct *mm)
708 {
709         VM_BUG_ON(atomic_read(&mm->mm_users));
710 
711         uprobe_clear_state(mm);
712         exit_aio(mm);
713         ksm_exit(mm);
714         khugepaged_exit(mm); /* must run before exit_mmap */
715         exit_mmap(mm);
716         set_mm_exe_file(mm, NULL);
717         if (!list_empty(&mm->mmlist)) {
718                 spin_lock(&mmlist_lock);
719                 list_del(&mm->mmlist);
720                 spin_unlock(&mmlist_lock);
721         }
722         if (mm->binfmt)
723                 module_put(mm->binfmt->module);
724         mmdrop(mm);
725 }
726 
727 /*
728  * Decrement the use count and release all resources for an mm.
729  */
730 void mmput(struct mm_struct *mm)
731 {
732         might_sleep();
733 
734         if (atomic_dec_and_test(&mm->mm_users))
735                 __mmput(mm);
736 }
737 EXPORT_SYMBOL_GPL(mmput);
738 
739 #ifdef CONFIG_MMU
740 static void mmput_async_fn(struct work_struct *work)
741 {
742         struct mm_struct *mm = container_of(work, struct mm_struct, async_put_work);
743         __mmput(mm);
744 }
745 
746 void mmput_async(struct mm_struct *mm)
747 {
748         if (atomic_dec_and_test(&mm->mm_users)) {
749                 INIT_WORK(&mm->async_put_work, mmput_async_fn);
750                 schedule_work(&mm->async_put_work);
751         }
752 }
753 #endif
754 
755 /**
756  * set_mm_exe_file - change a reference to the mm's executable file
757  *
758  * This changes mm's executable file (shown as symlink /proc/[pid]/exe).
759  *
760  * Main users are mmput() and sys_execve(). Callers prevent concurrent
761  * invocations: in mmput() nobody alive left, in execve task is single
762  * threaded. sys_prctl(PR_SET_MM_MAP/EXE_FILE) also needs to set the
763  * mm->exe_file, but does so without using set_mm_exe_file() in order
764  * to do avoid the need for any locks.
765  */
766 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
767 {
768         struct file *old_exe_file;
769 
770         /*
771          * It is safe to dereference the exe_file without RCU as
772          * this function is only called if nobody else can access
773          * this mm -- see comment above for justification.
774          */
775         old_exe_file = rcu_dereference_raw(mm->exe_file);
776 
777         if (new_exe_file)
778                 get_file(new_exe_file);
779         rcu_assign_pointer(mm->exe_file, new_exe_file);
780         if (old_exe_file)
781                 fput(old_exe_file);
782 }
783 
784 /**
785  * get_mm_exe_file - acquire a reference to the mm's executable file
786  *
787  * Returns %NULL if mm has no associated executable file.
788  * User must release file via fput().
789  */
790 struct file *get_mm_exe_file(struct mm_struct *mm)
791 {
792         struct file *exe_file;
793 
794         rcu_read_lock();
795         exe_file = rcu_dereference(mm->exe_file);
796         if (exe_file && !get_file_rcu(exe_file))
797                 exe_file = NULL;
798         rcu_read_unlock();
799         return exe_file;
800 }
801 EXPORT_SYMBOL(get_mm_exe_file);
802 
803 /**
804  * get_task_mm - acquire a reference to the task's mm
805  *
806  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
807  * this kernel workthread has transiently adopted a user mm with use_mm,
808  * to do its AIO) is not set and if so returns a reference to it, after
809  * bumping up the use count.  User must release the mm via mmput()
810  * after use.  Typically used by /proc and ptrace.
811  */
812 struct mm_struct *get_task_mm(struct task_struct *task)
813 {
814         struct mm_struct *mm;
815 
816         task_lock(task);
817         mm = task->mm;
818         if (mm) {
819                 if (task->flags & PF_KTHREAD)
820                         mm = NULL;
821                 else
822                         atomic_inc(&mm->mm_users);
823         }
824         task_unlock(task);
825         return mm;
826 }
827 EXPORT_SYMBOL_GPL(get_task_mm);
828 
829 struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
830 {
831         struct mm_struct *mm;
832         int err;
833 
834         err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
835         if (err)
836                 return ERR_PTR(err);
837 
838         mm = get_task_mm(task);
839         if (mm && mm != current->mm &&
840                         !ptrace_may_access(task, mode)) {
841                 mmput(mm);
842                 mm = ERR_PTR(-EACCES);
843         }
844         mutex_unlock(&task->signal->cred_guard_mutex);
845 
846         return mm;
847 }
848 
849 static void complete_vfork_done(struct task_struct *tsk)
850 {
851         struct completion *vfork;
852 
853         task_lock(tsk);
854         vfork = tsk->vfork_done;
855         if (likely(vfork)) {
856                 tsk->vfork_done = NULL;
857                 complete(vfork);
858         }
859         task_unlock(tsk);
860 }
861 
862 static int wait_for_vfork_done(struct task_struct *child,
863                                 struct completion *vfork)
864 {
865         int killed;
866 
867         freezer_do_not_count();
868         killed = wait_for_completion_killable(vfork);
869         freezer_count();
870 
871         if (killed) {
872                 task_lock(child);
873                 child->vfork_done = NULL;
874                 task_unlock(child);
875         }
876 
877         put_task_struct(child);
878         return killed;
879 }
880 
881 /* Please note the differences between mmput and mm_release.
882  * mmput is called whenever we stop holding onto a mm_struct,
883  * error success whatever.
884  *
885  * mm_release is called after a mm_struct has been removed
886  * from the current process.
887  *
888  * This difference is important for error handling, when we
889  * only half set up a mm_struct for a new process and need to restore
890  * the old one.  Because we mmput the new mm_struct before
891  * restoring the old one. . .
892  * Eric Biederman 10 January 1998
893  */
894 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
895 {
896         /* Get rid of any futexes when releasing the mm */
897 #ifdef CONFIG_FUTEX
898         if (unlikely(tsk->robust_list)) {
899                 exit_robust_list(tsk);
900                 tsk->robust_list = NULL;
901         }
902 #ifdef CONFIG_COMPAT
903         if (unlikely(tsk->compat_robust_list)) {
904                 compat_exit_robust_list(tsk);
905                 tsk->compat_robust_list = NULL;
906         }
907 #endif
908         if (unlikely(!list_empty(&tsk->pi_state_list)))
909                 exit_pi_state_list(tsk);
910 #endif
911 
912         uprobe_free_utask(tsk);
913 
914         /* Get rid of any cached register state */
915         deactivate_mm(tsk, mm);
916 
917         /*
918          * If we're exiting normally, clear a user-space tid field if
919          * requested.  We leave this alone when dying by signal, to leave
920          * the value intact in a core dump, and to save the unnecessary
921          * trouble, say, a killed vfork parent shouldn't touch this mm.
922          * Userland only wants this done for a sys_exit.
923          */
924         if (tsk->clear_child_tid) {
925                 if (!(tsk->flags & PF_SIGNALED) &&
926                     atomic_read(&mm->mm_users) > 1) {
927                         /*
928                          * We don't check the error code - if userspace has
929                          * not set up a proper pointer then tough luck.
930                          */
931                         put_user(0, tsk->clear_child_tid);
932                         sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
933                                         1, NULL, NULL, 0);
934                 }
935                 tsk->clear_child_tid = NULL;
936         }
937 
938         /*
939          * All done, finally we can wake up parent and return this mm to him.
940          * Also kthread_stop() uses this completion for synchronization.
941          */
942         if (tsk->vfork_done)
943                 complete_vfork_done(tsk);
944 }
945 
946 /*
947  * Allocate a new mm structure and copy contents from the
948  * mm structure of the passed in task structure.
949  */
950 static struct mm_struct *dup_mm(struct task_struct *tsk)
951 {
952         struct mm_struct *mm, *oldmm = current->mm;
953         int err;
954 
955         mm = allocate_mm();
956         if (!mm)
957                 goto fail_nomem;
958 
959         memcpy(mm, oldmm, sizeof(*mm));
960 
961         if (!mm_init(mm, tsk))
962                 goto fail_nomem;
963 
964         err = dup_mmap(mm, oldmm);
965         if (err)
966                 goto free_pt;
967 
968         mm->hiwater_rss = get_mm_rss(mm);
969         mm->hiwater_vm = mm->total_vm;
970 
971         if (mm->binfmt && !try_module_get(mm->binfmt->module))
972                 goto free_pt;
973 
974         return mm;
975 
976 free_pt:
977         /* don't put binfmt in mmput, we haven't got module yet */
978         mm->binfmt = NULL;
979         mmput(mm);
980 
981 fail_nomem:
982         return NULL;
983 }
984 
985 static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
986 {
987         struct mm_struct *mm, *oldmm;
988         int retval;
989 
990         tsk->min_flt = tsk->maj_flt = 0;
991         tsk->nvcsw = tsk->nivcsw = 0;
992 #ifdef CONFIG_DETECT_HUNG_TASK
993         tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
994 #endif
995 
996         tsk->mm = NULL;
997         tsk->active_mm = NULL;
998 
999         /*
1000          * Are we cloning a kernel thread?
1001          *
1002          * We need to steal a active VM for that..
1003          */
1004         oldmm = current->mm;
1005         if (!oldmm)
1006                 return 0;
1007 
1008         /* initialize the new vmacache entries */
1009         vmacache_flush(tsk);
1010 
1011         if (clone_flags & CLONE_VM) {
1012                 atomic_inc(&oldmm->mm_users);
1013                 mm = oldmm;
1014                 goto good_mm;
1015         }
1016 
1017         retval = -ENOMEM;
1018         mm = dup_mm(tsk);
1019         if (!mm)
1020                 goto fail_nomem;
1021 
1022 good_mm:
1023         tsk->mm = mm;
1024         tsk->active_mm = mm;
1025         return 0;
1026 
1027 fail_nomem:
1028         return retval;
1029 }
1030 
1031 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
1032 {
1033         struct fs_struct *fs = current->fs;
1034         if (clone_flags & CLONE_FS) {
1035                 /* tsk->fs is already what we want */
1036                 spin_lock(&fs->lock);
1037                 if (fs->in_exec) {
1038                         spin_unlock(&fs->lock);
1039                         return -EAGAIN;
1040                 }
1041                 fs->users++;
1042                 spin_unlock(&fs->lock);
1043                 return 0;
1044         }
1045         tsk->fs = copy_fs_struct(fs);
1046         if (!tsk->fs)
1047                 return -ENOMEM;
1048         return 0;
1049 }
1050 
1051 static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
1052 {
1053         struct files_struct *oldf, *newf;
1054         int error = 0;
1055 
1056         /*
1057          * A background process may not have any files ...
1058          */
1059         oldf = current->files;
1060         if (!oldf)
1061                 goto out;
1062 
1063         if (clone_flags & CLONE_FILES) {
1064                 atomic_inc(&oldf->count);
1065                 goto out;
1066         }
1067 
1068         newf = dup_fd(oldf, &error);
1069         if (!newf)
1070                 goto out;
1071 
1072         tsk->files = newf;
1073         error = 0;
1074 out:
1075         return error;
1076 }
1077 
1078 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
1079 {
1080 #ifdef CONFIG_BLOCK
1081         struct io_context *ioc = current->io_context;
1082         struct io_context *new_ioc;
1083 
1084         if (!ioc)
1085                 return 0;
1086         /*
1087          * Share io context with parent, if CLONE_IO is set
1088          */
1089         if (clone_flags & CLONE_IO) {
1090                 ioc_task_link(ioc);
1091                 tsk->io_context = ioc;
1092         } else if (ioprio_valid(ioc->ioprio)) {
1093                 new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
1094                 if (unlikely(!new_ioc))
1095                         return -ENOMEM;
1096 
1097                 new_ioc->ioprio = ioc->ioprio;
1098                 put_io_context(new_ioc);
1099         }
1100 #endif
1101         return 0;
1102 }
1103 
1104 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
1105 {
1106         struct sighand_struct *sig;
1107 
1108         if (clone_flags & CLONE_SIGHAND) {
1109                 atomic_inc(&current->sighand->count);
1110                 return 0;
1111         }
1112         sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
1113         rcu_assign_pointer(tsk->sighand, sig);
1114         if (!sig)
1115                 return -ENOMEM;
1116 
1117         atomic_set(&sig->count, 1);
1118         memcpy(sig->action, current->sighand->action, sizeof(sig->action));
1119         return 0;
1120 }
1121 
1122 void __cleanup_sighand(struct sighand_struct *sighand)
1123 {
1124         if (atomic_dec_and_test(&sighand->count)) {
1125                 signalfd_cleanup(sighand);
1126                 /*
1127                  * sighand_cachep is SLAB_DESTROY_BY_RCU so we can free it
1128                  * without an RCU grace period, see __lock_task_sighand().
1129                  */
1130                 kmem_cache_free(sighand_cachep, sighand);
1131         }
1132 }
1133 
1134 /*
1135  * Initialize POSIX timer handling for a thread group.
1136  */
1137 static void posix_cpu_timers_init_group(struct signal_struct *sig)
1138 {
1139         unsigned long cpu_limit;
1140 
1141         cpu_limit = READ_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1142         if (cpu_limit != RLIM_INFINITY) {
1143                 sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
1144                 sig->cputimer.running = true;
1145         }
1146 
1147         /* The timer lists. */
1148         INIT_LIST_HEAD(&sig->cpu_timers[0]);
1149         INIT_LIST_HEAD(&sig->cpu_timers[1]);
1150         INIT_LIST_HEAD(&sig->cpu_timers[2]);
1151 }
1152 
1153 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1154 {
1155         struct signal_struct *sig;
1156 
1157         if (clone_flags & CLONE_THREAD)
1158                 return 0;
1159 
1160         sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1161         tsk->signal = sig;
1162         if (!sig)
1163                 return -ENOMEM;
1164 
1165         sig->nr_threads = 1;
1166         atomic_set(&sig->live, 1);
1167         atomic_set(&sig->sigcnt, 1);
1168 
1169         /* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */
1170         sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node);
1171         tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);
1172 
1173         init_waitqueue_head(&sig->wait_chldexit);
1174         sig->curr_target = tsk;
1175         init_sigpending(&sig->shared_pending);
1176         INIT_LIST_HEAD(&sig->posix_timers);
1177         seqlock_init(&sig->stats_lock);
1178         prev_cputime_init(&sig->prev_cputime);
1179 
1180         hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1181         sig->real_timer.function = it_real_fn;
1182 
1183         task_lock(current->group_leader);
1184         memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1185         task_unlock(current->group_leader);
1186 
1187         posix_cpu_timers_init_group(sig);
1188 
1189         tty_audit_fork(sig);
1190         sched_autogroup_fork(sig);
1191 
1192         sig->oom_score_adj = current->signal->oom_score_adj;
1193         sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1194 
1195         sig->has_child_subreaper = current->signal->has_child_subreaper ||
1196                                    current->signal->is_child_subreaper;
1197 
1198         mutex_init(&sig->cred_guard_mutex);
1199 
1200         return 0;
1201 }
1202 
1203 static void copy_seccomp(struct task_struct *p)
1204 {
1205 #ifdef CONFIG_SECCOMP
1206         /*
1207          * Must be called with sighand->lock held, which is common to
1208          * all threads in the group. Holding cred_guard_mutex is not
1209          * needed because this new task is not yet running and cannot
1210          * be racing exec.
1211          */
1212         assert_spin_locked(&current->sighand->siglock);
1213 
1214         /* Ref-count the new filter user, and assign it. */
1215         get_seccomp_filter(current);
1216         p->seccomp = current->seccomp;
1217 
1218         /*
1219          * Explicitly enable no_new_privs here in case it got set
1220          * between the task_struct being duplicated and holding the
1221          * sighand lock. The seccomp state and nnp must be in sync.
1222          */
1223         if (task_no_new_privs(current))
1224                 task_set_no_new_privs(p);
1225 
1226         /*
1227          * If the parent gained a seccomp mode after copying thread
1228          * flags and between before we held the sighand lock, we have
1229          * to manually enable the seccomp thread flag here.
1230          */
1231         if (p->seccomp.mode != SECCOMP_MODE_DISABLED)
1232                 set_tsk_thread_flag(p, TIF_SECCOMP);
1233 #endif
1234 }
1235 
1236 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1237 {
1238         current->clear_child_tid = tidptr;
1239 
1240         return task_pid_vnr(current);
1241 }
1242 
1243 static void rt_mutex_init_task(struct task_struct *p)
1244 {
1245         raw_spin_lock_init(&p->pi_lock);
1246 #ifdef CONFIG_RT_MUTEXES
1247         p->pi_waiters = RB_ROOT;
1248         p->pi_waiters_leftmost = NULL;
1249         p->pi_blocked_on = NULL;
1250 #endif
1251 }
1252 
1253 /*
1254  * Initialize POSIX timer handling for a single task.
1255  */
1256 static void posix_cpu_timers_init(struct task_struct *tsk)
1257 {
1258         tsk->cputime_expires.prof_exp = 0;
1259         tsk->cputime_expires.virt_exp = 0;
1260         tsk->cputime_expires.sched_exp = 0;
1261         INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1262         INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1263         INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1264 }
1265 
1266 static inline void
1267 init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
1268 {
1269          task->pids[type].pid = pid;
1270 }
1271 
1272 /*
1273  * This creates a new process as a copy of the old one,
1274  * but does not actually start it yet.
1275  *
1276  * It copies the registers, and all the appropriate
1277  * parts of the process environment (as per the clone
1278  * flags). The actual kick-off is left to the caller.
1279  */
1280 static struct task_struct *copy_process(unsigned long clone_flags,
1281                                         unsigned long stack_start,
1282                                         unsigned long stack_size,
1283                                         int __user *child_tidptr,
1284                                         struct pid *pid,
1285                                         int trace,
1286                                         unsigned long tls,
1287                                         int node)
1288 {
1289         int retval;
1290         struct task_struct *p;
1291 
1292         if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1293                 return ERR_PTR(-EINVAL);
1294 
1295         if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
1296                 return ERR_PTR(-EINVAL);
1297 
1298         /*
1299          * Thread groups must share signals as well, and detached threads
1300          * can only be started up within the thread group.
1301          */
1302         if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1303                 return ERR_PTR(-EINVAL);
1304 
1305         /*
1306          * Shared signal handlers imply shared VM. By way of the above,
1307          * thread groups also imply shared VM. Blocking this case allows
1308          * for various simplifications in other code.
1309          */
1310         if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1311                 return ERR_PTR(-EINVAL);
1312 
1313         /*
1314          * Siblings of global init remain as zombies on exit since they are
1315          * not reaped by their parent (swapper). To solve this and to avoid
1316          * multi-rooted process trees, prevent global and container-inits
1317          * from creating siblings.
1318          */
1319         if ((clone_flags & CLONE_PARENT) &&
1320                                 current->signal->flags & SIGNAL_UNKILLABLE)
1321                 return ERR_PTR(-EINVAL);
1322 
1323         /*
1324          * If the new process will be in a different pid or user namespace
1325          * do not allow it to share a thread group with the forking task.
1326          */
1327         if (clone_flags & CLONE_THREAD) {
1328                 if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
1329                     (task_active_pid_ns(current) !=
1330                                 current->nsproxy->pid_ns_for_children))
1331                         return ERR_PTR(-EINVAL);
1332         }
1333 
1334         retval = security_task_create(clone_flags);
1335         if (retval)
1336                 goto fork_out;
1337 
1338         retval = -ENOMEM;
1339         p = dup_task_struct(current, node);
1340         if (!p)
1341                 goto fork_out;
1342 
1343         ftrace_graph_init_task(p);
1344 
1345         rt_mutex_init_task(p);
1346 
1347 #ifdef CONFIG_PROVE_LOCKING
1348         DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1349         DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1350 #endif
1351         retval = -EAGAIN;
1352         if (atomic_read(&p->real_cred->user->processes) >=
1353                         task_rlimit(p, RLIMIT_NPROC)) {
1354                 if (p->real_cred->user != INIT_USER &&
1355                     !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
1356                         goto bad_fork_free;
1357         }
1358         current->flags &= ~PF_NPROC_EXCEEDED;
1359 
1360         retval = copy_creds(p, clone_flags);
1361         if (retval < 0)
1362                 goto bad_fork_free;
1363 
1364         /*
1365          * If multiple threads are within copy_process(), then this check
1366          * triggers too late. This doesn't hurt, the check is only there
1367          * to stop root fork bombs.
1368          */
1369         retval = -EAGAIN;
1370         if (nr_threads >= max_threads)
1371                 goto bad_fork_cleanup_count;
1372 
1373         delayacct_tsk_init(p);  /* Must remain after dup_task_struct() */
1374         p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
1375         p->flags |= PF_FORKNOEXEC;
1376         INIT_LIST_HEAD(&p->children);
1377         INIT_LIST_HEAD(&p->sibling);
1378         rcu_copy_process(p);
1379         p->vfork_done = NULL;
1380         spin_lock_init(&p->alloc_lock);
1381 
1382         init_sigpending(&p->pending);
1383 
1384         p->utime = p->stime = p->gtime = 0;
1385         p->utimescaled = p->stimescaled = 0;
1386         prev_cputime_init(&p->prev_cputime);
1387 
1388 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
1389         seqcount_init(&p->vtime_seqcount);
1390         p->vtime_snap = 0;
1391         p->vtime_snap_whence = VTIME_INACTIVE;
1392 #endif
1393 
1394 #if defined(SPLIT_RSS_COUNTING)
1395         memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1396 #endif
1397 
1398         p->default_timer_slack_ns = current->timer_slack_ns;
1399 
1400         task_io_accounting_init(&p->ioac);
1401         acct_clear_integrals(p);
1402 
1403         posix_cpu_timers_init(p);
1404 
1405         p->start_time = ktime_get_ns();
1406         p->real_start_time = ktime_get_boot_ns();
1407         p->io_context = NULL;
1408         p->audit_context = NULL;
1409         threadgroup_change_begin(current);
1410         cgroup_fork(p);
1411 #ifdef CONFIG_NUMA
1412         p->mempolicy = mpol_dup(p->mempolicy);
1413         if (IS_ERR(p->mempolicy)) {
1414                 retval = PTR_ERR(p->mempolicy);
1415                 p->mempolicy = NULL;
1416                 goto bad_fork_cleanup_threadgroup_lock;
1417         }
1418 #endif
1419 #ifdef CONFIG_CPUSETS
1420         p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
1421         p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
1422         seqcount_init(&p->mems_allowed_seq);
1423 #endif
1424 #ifdef CONFIG_TRACE_IRQFLAGS
1425         p->irq_events = 0;
1426         p->hardirqs_enabled = 0;
1427         p->hardirq_enable_ip = 0;
1428         p->hardirq_enable_event = 0;
1429         p->hardirq_disable_ip = _THIS_IP_;
1430         p->hardirq_disable_event = 0;
1431         p->softirqs_enabled = 1;
1432         p->softirq_enable_ip = _THIS_IP_;
1433         p->softirq_enable_event = 0;
1434         p->softirq_disable_ip = 0;
1435         p->softirq_disable_event = 0;
1436         p->hardirq_context = 0;
1437         p->softirq_context = 0;
1438 #endif
1439 
1440         p->pagefault_disabled = 0;
1441 
1442 #ifdef CONFIG_LOCKDEP
1443         p->lockdep_depth = 0; /* no locks held yet */
1444         p->curr_chain_key = 0;
1445         p->lockdep_recursion = 0;
1446 #endif
1447 
1448 #ifdef CONFIG_DEBUG_MUTEXES
1449         p->blocked_on = NULL; /* not blocked yet */
1450 #endif
1451 #ifdef CONFIG_BCACHE
1452         p->sequential_io        = 0;
1453         p->sequential_io_avg    = 0;
1454 #endif
1455 
1456         /* Perform scheduler related setup. Assign this task to a CPU. */
1457         retval = sched_fork(clone_flags, p);
1458         if (retval)
1459                 goto bad_fork_cleanup_policy;
1460 
1461         retval = perf_event_init_task(p);
1462         if (retval)
1463                 goto bad_fork_cleanup_policy;
1464         retval = audit_alloc(p);
1465         if (retval)
1466                 goto bad_fork_cleanup_perf;
1467         /* copy all the process information */
1468         shm_init_task(p);
1469         retval = copy_semundo(clone_flags, p);
1470         if (retval)
1471                 goto bad_fork_cleanup_audit;
1472         retval = copy_files(clone_flags, p);
1473         if (retval)
1474                 goto bad_fork_cleanup_semundo;
1475         retval = copy_fs(clone_flags, p);
1476         if (retval)
1477                 goto bad_fork_cleanup_files;
1478         retval = copy_sighand(clone_flags, p);
1479         if (retval)
1480                 goto bad_fork_cleanup_fs;
1481         retval = copy_signal(clone_flags, p);
1482         if (retval)
1483                 goto bad_fork_cleanup_sighand;
1484         retval = copy_mm(clone_flags, p);
1485         if (retval)
1486                 goto bad_fork_cleanup_signal;
1487         retval = copy_namespaces(clone_flags, p);
1488         if (retval)
1489                 goto bad_fork_cleanup_mm;
1490         retval = copy_io(clone_flags, p);
1491         if (retval)
1492                 goto bad_fork_cleanup_namespaces;
1493         retval = copy_thread_tls(clone_flags, stack_start, stack_size, p, tls);
1494         if (retval)
1495                 goto bad_fork_cleanup_io;
1496 
1497         if (pid != &init_struct_pid) {
1498                 pid = alloc_pid(p->nsproxy->pid_ns_for_children);
1499                 if (IS_ERR(pid)) {
1500                         retval = PTR_ERR(pid);
1501                         goto bad_fork_cleanup_thread;
1502                 }
1503         }
1504 
1505         p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1506         /*
1507          * Clear TID on mm_release()?
1508          */
1509         p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
1510 #ifdef CONFIG_BLOCK
1511         p->plug = NULL;
1512 #endif
1513 #ifdef CONFIG_FUTEX
1514         p->robust_list = NULL;
1515 #ifdef CONFIG_COMPAT
1516         p->compat_robust_list = NULL;
1517 #endif
1518         INIT_LIST_HEAD(&p->pi_state_list);
1519         p->pi_state_cache = NULL;
1520 #endif
1521         /*
1522          * sigaltstack should be cleared when sharing the same VM
1523          */
1524         if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1525                 sas_ss_reset(p);
1526 
1527         /*
1528          * Syscall tracing and stepping should be turned off in the
1529          * child regardless of CLONE_PTRACE.
1530          */
1531         user_disable_single_step(p);
1532         clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1533 #ifdef TIF_SYSCALL_EMU
1534         clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1535 #endif
1536         clear_all_latency_tracing(p);
1537 
1538         /* ok, now we should be set up.. */
1539         p->pid = pid_nr(pid);
1540         if (clone_flags & CLONE_THREAD) {
1541                 p->exit_signal = -1;
1542                 p->group_leader = current->group_leader;
1543                 p->tgid = current->tgid;
1544         } else {
1545                 if (clone_flags & CLONE_PARENT)
1546                         p->exit_signal = current->group_leader->exit_signal;
1547                 else
1548                         p->exit_signal = (clone_flags & CSIGNAL);
1549                 p->group_leader = p;
1550                 p->tgid = p->pid;
1551         }
1552 
1553         p->nr_dirtied = 0;
1554         p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
1555         p->dirty_paused_when = 0;
1556 
1557         p->pdeath_signal = 0;
1558         INIT_LIST_HEAD(&p->thread_group);
1559         p->task_works = NULL;
1560 
1561         /*
1562          * Ensure that the cgroup subsystem policies allow the new process to be
1563          * forked. It should be noted the the new process's css_set can be changed
1564          * between here and cgroup_post_fork() if an organisation operation is in
1565          * progress.
1566          */
1567         retval = cgroup_can_fork(p);
1568         if (retval)
1569                 goto bad_fork_free_pid;
1570 
1571         /*
1572          * Make it visible to the rest of the system, but dont wake it up yet.
1573          * Need tasklist lock for parent etc handling!
1574          */
1575         write_lock_irq(&tasklist_lock);
1576 
1577         /* CLONE_PARENT re-uses the old parent */
1578         if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1579                 p->real_parent = current->real_parent;
1580                 p->parent_exec_id = current->parent_exec_id;
1581         } else {
1582                 p->real_parent = current;
1583                 p->parent_exec_id = current->self_exec_id;
1584         }
1585 
1586         spin_lock(&current->sighand->siglock);
1587 
1588         /*
1589          * Copy seccomp details explicitly here, in case they were changed
1590          * before holding sighand lock.
1591          */
1592         copy_seccomp(p);
1593 
1594         /*
1595          * Process group and session signals need to be delivered to just the
1596          * parent before the fork or both the parent and the child after the
1597          * fork. Restart if a signal comes in before we add the new process to
1598          * it's process group.
1599          * A fatal signal pending means that current will exit, so the new
1600          * thread can't slip out of an OOM kill (or normal SIGKILL).
1601         */
1602         recalc_sigpending();
1603         if (signal_pending(current)) {
1604                 spin_unlock(&current->sighand->siglock);
1605                 write_unlock_irq(&tasklist_lock);
1606                 retval = -ERESTARTNOINTR;
1607                 goto bad_fork_cancel_cgroup;
1608         }
1609 
1610         if (likely(p->pid)) {
1611                 ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
1612 
1613                 init_task_pid(p, PIDTYPE_PID, pid);
1614                 if (thread_group_leader(p)) {
1615                         init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
1616                         init_task_pid(p, PIDTYPE_SID, task_session(current));
1617 
1618                         if (is_child_reaper(pid)) {
1619                                 ns_of_pid(pid)->child_reaper = p;
1620                                 p->signal->flags |= SIGNAL_UNKILLABLE;
1621                         }
1622 
1623                         p->signal->leader_pid = pid;
1624                         p->signal->tty = tty_kref_get(current->signal->tty);
1625                         list_add_tail(&p->sibling, &p->real_parent->children);
1626                         list_add_tail_rcu(&p->tasks, &init_task.tasks);
1627                         attach_pid(p, PIDTYPE_PGID);
1628                         attach_pid(p, PIDTYPE_SID);
1629                         __this_cpu_inc(process_counts);
1630                 } else {
1631                         current->signal->nr_threads++;
1632                         atomic_inc(&current->signal->live);
1633                         atomic_inc(&current->signal->sigcnt);
1634                         list_add_tail_rcu(&p->thread_group,
1635                                           &p->group_leader->thread_group);
1636                         list_add_tail_rcu(&p->thread_node,
1637                                           &p->signal->thread_head);
1638                 }
1639                 attach_pid(p, PIDTYPE_PID);
1640                 nr_threads++;
1641         }
1642 
1643         total_forks++;
1644         spin_unlock(&current->sighand->siglock);
1645         syscall_tracepoint_update(p);
1646         write_unlock_irq(&tasklist_lock);
1647 
1648         proc_fork_connector(p);
1649         cgroup_post_fork(p);
1650         threadgroup_change_end(current);
1651         perf_event_fork(p);
1652 
1653         trace_task_newtask(p, clone_flags);
1654         uprobe_copy_process(p, clone_flags);
1655 
1656         return p;
1657 
1658 bad_fork_cancel_cgroup:
1659         cgroup_cancel_fork(p);
1660 bad_fork_free_pid:
1661         if (pid != &init_struct_pid)
1662                 free_pid(pid);
1663 bad_fork_cleanup_thread:
1664         exit_thread(p);
1665 bad_fork_cleanup_io:
1666         if (p->io_context)
1667                 exit_io_context(p);
1668 bad_fork_cleanup_namespaces:
1669         exit_task_namespaces(p);
1670 bad_fork_cleanup_mm:
1671         if (p->mm)
1672                 mmput(p->mm);
1673 bad_fork_cleanup_signal:
1674         if (!(clone_flags & CLONE_THREAD))
1675                 free_signal_struct(p->signal);
1676 bad_fork_cleanup_sighand:
1677         __cleanup_sighand(p->sighand);
1678 bad_fork_cleanup_fs:
1679         exit_fs(p); /* blocking */
1680 bad_fork_cleanup_files:
1681         exit_files(p); /* blocking */
1682 bad_fork_cleanup_semundo:
1683         exit_sem(p);
1684 bad_fork_cleanup_audit:
1685         audit_free(p);
1686 bad_fork_cleanup_perf:
1687         perf_event_free_task(p);
1688 bad_fork_cleanup_policy:
1689 #ifdef CONFIG_NUMA
1690         mpol_put(p->mempolicy);
1691 bad_fork_cleanup_threadgroup_lock:
1692 #endif
1693         threadgroup_change_end(current);
1694         delayacct_tsk_free(p);
1695 bad_fork_cleanup_count:
1696         atomic_dec(&p->cred->user->processes);
1697         exit_creds(p);
1698 bad_fork_free:
1699         free_task(p);
1700 fork_out:
1701         return ERR_PTR(retval);
1702 }
1703 
1704 static inline void init_idle_pids(struct pid_link *links)
1705 {
1706         enum pid_type type;
1707 
1708         for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1709                 INIT_HLIST_NODE(&links[type].node); /* not really needed */
1710                 links[type].pid = &init_struct_pid;
1711         }
1712 }
1713 
1714 struct task_struct *fork_idle(int cpu)
1715 {
1716         struct task_struct *task;
1717         task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0, 0,
1718                             cpu_to_node(cpu));
1719         if (!IS_ERR(task)) {
1720                 init_idle_pids(task->pids);
1721                 init_idle(task, cpu);
1722         }
1723 
1724         return task;
1725 }
1726 
1727 /*
1728  *  Ok, this is the main fork-routine.
1729  *
1730  * It copies the process, and if successful kick-starts
1731  * it and waits for it to finish using the VM if required.
1732  */
1733 long _do_fork(unsigned long clone_flags,
1734               unsigned long stack_start,
1735               unsigned long stack_size,
1736               int __user *parent_tidptr,
1737               int __user *child_tidptr,
1738               unsigned long tls)
1739 {
1740         struct task_struct *p;
1741         int trace = 0;
1742         long nr;
1743 
1744         /*
1745          * Determine whether and which event to report to ptracer.  When
1746          * called from kernel_thread or CLONE_UNTRACED is explicitly
1747          * requested, no event is reported; otherwise, report if the event
1748          * for the type of forking is enabled.
1749          */
1750         if (!(clone_flags & CLONE_UNTRACED)) {
1751                 if (clone_flags & CLONE_VFORK)
1752                         trace = PTRACE_EVENT_VFORK;
1753                 else if ((clone_flags & CSIGNAL) != SIGCHLD)
1754                         trace = PTRACE_EVENT_CLONE;
1755                 else
1756                         trace = PTRACE_EVENT_FORK;
1757 
1758                 if (likely(!ptrace_event_enabled(current, trace)))
1759                         trace = 0;
1760         }
1761 
1762         p = copy_process(clone_flags, stack_start, stack_size,
1763                          child_tidptr, NULL, trace, tls, NUMA_NO_NODE);
1764         /*
1765          * Do this prior waking up the new thread - the thread pointer
1766          * might get invalid after that point, if the thread exits quickly.
1767          */
1768         if (!IS_ERR(p)) {
1769                 struct completion vfork;
1770                 struct pid *pid;
1771 
1772                 trace_sched_process_fork(current, p);
1773 
1774                 pid = get_task_pid(p, PIDTYPE_PID);
1775                 nr = pid_vnr(pid);
1776 
1777                 if (clone_flags & CLONE_PARENT_SETTID)
1778                         put_user(nr, parent_tidptr);
1779 
1780                 if (clone_flags & CLONE_VFORK) {
1781                         p->vfork_done = &vfork;
1782                         init_completion(&vfork);
1783                         get_task_struct(p);
1784                 }
1785 
1786                 wake_up_new_task(p);
1787 
1788                 /* forking complete and child started to run, tell ptracer */
1789                 if (unlikely(trace))
1790                         ptrace_event_pid(trace, pid);
1791 
1792                 if (clone_flags & CLONE_VFORK) {
1793                         if (!wait_for_vfork_done(p, &vfork))
1794                                 ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
1795                 }
1796 
1797                 put_pid(pid);
1798         } else {
1799                 nr = PTR_ERR(p);
1800         }
1801         return nr;
1802 }
1803 
1804 #ifndef CONFIG_HAVE_COPY_THREAD_TLS
1805 /* For compatibility with architectures that call do_fork directly rather than
1806  * using the syscall entry points below. */
1807 long do_fork(unsigned long clone_flags,
1808               unsigned long stack_start,
1809               unsigned long stack_size,
1810               int __user *parent_tidptr,
1811               int __user *child_tidptr)
1812 {
1813         return _do_fork(clone_flags, stack_start, stack_size,
1814                         parent_tidptr, child_tidptr, 0);
1815 }
1816 #endif
1817 
1818 /*
1819  * Create a kernel thread.
1820  */
1821 pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
1822 {
1823         return _do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
1824                 (unsigned long)arg, NULL, NULL, 0);
1825 }
1826 
1827 #ifdef __ARCH_WANT_SYS_FORK
1828 SYSCALL_DEFINE0(fork)
1829 {
1830 #ifdef CONFIG_MMU
1831         return _do_fork(SIGCHLD, 0, 0, NULL, NULL, 0);
1832 #else
1833         /* can not support in nommu mode */
1834         return -EINVAL;
1835 #endif
1836 }
1837 #endif
1838 
1839 #ifdef __ARCH_WANT_SYS_VFORK
1840 SYSCALL_DEFINE0(vfork)
1841 {
1842         return _do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0,
1843                         0, NULL, NULL, 0);
1844 }
1845 #endif
1846 
1847 #ifdef __ARCH_WANT_SYS_CLONE
1848 #ifdef CONFIG_CLONE_BACKWARDS
1849 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1850                  int __user *, parent_tidptr,
1851                  unsigned long, tls,
1852                  int __user *, child_tidptr)
1853 #elif defined(CONFIG_CLONE_BACKWARDS2)
1854 SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
1855                  int __user *, parent_tidptr,
1856                  int __user *, child_tidptr,
1857                  unsigned long, tls)
1858 #elif defined(CONFIG_CLONE_BACKWARDS3)
1859 SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
1860                 int, stack_size,
1861                 int __user *, parent_tidptr,
1862                 int __user *, child_tidptr,
1863                 unsigned long, tls)
1864 #else
1865 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1866                  int __user *, parent_tidptr,
1867                  int __user *, child_tidptr,
1868                  unsigned long, tls)
1869 #endif
1870 {
1871         return _do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr, tls);
1872 }
1873 #endif
1874 
1875 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1876 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1877 #endif
1878 
1879 static void sighand_ctor(void *data)
1880 {
1881         struct sighand_struct *sighand = data;
1882 
1883         spin_lock_init(&sighand->siglock);
1884         init_waitqueue_head(&sighand->signalfd_wqh);
1885 }
1886 
1887 void __init proc_caches_init(void)
1888 {
1889         sighand_cachep = kmem_cache_create("sighand_cache",
1890                         sizeof(struct sighand_struct), 0,
1891                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1892                         SLAB_NOTRACK|SLAB_ACCOUNT, sighand_ctor);
1893         signal_cachep = kmem_cache_create("signal_cache",
1894                         sizeof(struct signal_struct), 0,
1895                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK|SLAB_ACCOUNT,
1896                         NULL);
1897         files_cachep = kmem_cache_create("files_cache",
1898                         sizeof(struct files_struct), 0,
1899                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK|SLAB_ACCOUNT,
1900                         NULL);
1901         fs_cachep = kmem_cache_create("fs_cache",
1902                         sizeof(struct fs_struct), 0,
1903                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK|SLAB_ACCOUNT,
1904                         NULL);
1905         /*
1906          * FIXME! The "sizeof(struct mm_struct)" currently includes the
1907          * whole struct cpumask for the OFFSTACK case. We could change
1908          * this to *only* allocate as much of it as required by the
1909          * maximum number of CPU's we can ever have.  The cpumask_allocation
1910          * is at the end of the structure, exactly for that reason.
1911          */
1912         mm_cachep = kmem_cache_create("mm_struct",
1913                         sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1914                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK|SLAB_ACCOUNT,
1915                         NULL);
1916         vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_ACCOUNT);
1917         mmap_init();
1918         nsproxy_cache_init();
1919 }
1920 
1921 /*
1922  * Check constraints on flags passed to the unshare system call.
1923  */
1924 static int check_unshare_flags(unsigned long unshare_flags)
1925 {
1926         if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1927                                 CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1928                                 CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
1929                                 CLONE_NEWUSER|CLONE_NEWPID|CLONE_NEWCGROUP))
1930                 return -EINVAL;
1931         /*
1932          * Not implemented, but pretend it works if there is nothing
1933          * to unshare.  Note that unsharing the address space or the
1934          * signal handlers also need to unshare the signal queues (aka
1935          * CLONE_THREAD).
1936          */
1937         if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
1938                 if (!thread_group_empty(current))
1939                         return -EINVAL;
1940         }
1941         if (unshare_flags & (CLONE_SIGHAND | CLONE_VM)) {
1942                 if (atomic_read(&current->sighand->count) > 1)
1943                         return -EINVAL;
1944         }
1945         if (unshare_flags & CLONE_VM) {
1946                 if (!current_is_single_threaded())
1947                         return -EINVAL;
1948         }
1949 
1950         return 0;
1951 }
1952 
1953 /*
1954  * Unshare the filesystem structure if it is being shared
1955  */
1956 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1957 {
1958         struct fs_struct *fs = current->fs;
1959 
1960         if (!(unshare_flags & CLONE_FS) || !fs)
1961                 return 0;
1962 
1963         /* don't need lock here; in the worst case we'll do useless copy */
1964         if (fs->users == 1)
1965                 return 0;
1966 
1967         *new_fsp = copy_fs_struct(fs);
1968         if (!*new_fsp)
1969                 return -ENOMEM;
1970 
1971         return 0;
1972 }
1973 
1974 /*
1975  * Unshare file descriptor table if it is being shared
1976  */
1977 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1978 {
1979         struct files_struct *fd = current->files;
1980         int error = 0;
1981 
1982         if ((unshare_flags & CLONE_FILES) &&
1983             (fd && atomic_read(&fd->count) > 1)) {
1984                 *new_fdp = dup_fd(fd, &error);
1985                 if (!*new_fdp)
1986                         return error;
1987         }
1988 
1989         return 0;
1990 }
1991 
1992 /*
1993  * unshare allows a process to 'unshare' part of the process
1994  * context which was originally shared using clone.  copy_*
1995  * functions used by do_fork() cannot be used here directly
1996  * because they modify an inactive task_struct that is being
1997  * constructed. Here we are modifying the current, active,
1998  * task_struct.
1999  */
2000 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
2001 {
2002         struct fs_struct *fs, *new_fs = NULL;
2003         struct files_struct *fd, *new_fd = NULL;
2004         struct cred *new_cred = NULL;
2005         struct nsproxy *new_nsproxy = NULL;
2006         int do_sysvsem = 0;
2007         int err;
2008 
2009         /*
2010          * If unsharing a user namespace must also unshare the thread group
2011          * and unshare the filesystem root and working directories.
2012          */
2013         if (unshare_flags & CLONE_NEWUSER)
2014                 unshare_flags |= CLONE_THREAD | CLONE_FS;
2015         /*
2016          * If unsharing vm, must also unshare signal handlers.
2017          */
2018         if (unshare_flags & CLONE_VM)
2019                 unshare_flags |= CLONE_SIGHAND;
2020         /*
2021          * If unsharing a signal handlers, must also unshare the signal queues.
2022          */
2023         if (unshare_flags & CLONE_SIGHAND)
2024                 unshare_flags |= CLONE_THREAD;
2025         /*
2026          * If unsharing namespace, must also unshare filesystem information.
2027          */
2028         if (unshare_flags & CLONE_NEWNS)
2029                 unshare_flags |= CLONE_FS;
2030 
2031         err = check_unshare_flags(unshare_flags);
2032         if (err)
2033                 goto bad_unshare_out;
2034         /*
2035          * CLONE_NEWIPC must also detach from the undolist: after switching
2036          * to a new ipc namespace, the semaphore arrays from the old
2037          * namespace are unreachable.
2038          */
2039         if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
2040                 do_sysvsem = 1;
2041         err = unshare_fs(unshare_flags, &new_fs);
2042         if (err)
2043                 goto bad_unshare_out;
2044         err = unshare_fd(unshare_flags, &new_fd);
2045         if (err)
2046                 goto bad_unshare_cleanup_fs;
2047         err = unshare_userns(unshare_flags, &new_cred);
2048         if (err)
2049                 goto bad_unshare_cleanup_fd;
2050         err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
2051                                          new_cred, new_fs);
2052         if (err)
2053                 goto bad_unshare_cleanup_cred;
2054 
2055         if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
2056                 if (do_sysvsem) {
2057                         /*
2058                          * CLONE_SYSVSEM is equivalent to sys_exit().
2059                          */
2060                         exit_sem(current);
2061                 }
2062                 if (unshare_flags & CLONE_NEWIPC) {
2063                         /* Orphan segments in old ns (see sem above). */
2064                         exit_shm(current);
2065                         shm_init_task(current);
2066                 }
2067 
2068                 if (new_nsproxy)
2069                         switch_task_namespaces(current, new_nsproxy);
2070 
2071                 task_lock(current);
2072 
2073                 if (new_fs) {
2074                         fs = current->fs;
2075                         spin_lock(&fs->lock);
2076                         current->fs = new_fs;
2077                         if (--fs->users)
2078                                 new_fs = NULL;
2079                         else
2080                                 new_fs = fs;
2081                         spin_unlock(&fs->lock);
2082                 }
2083 
2084                 if (new_fd) {
2085                         fd = current->files;
2086                         current->files = new_fd;
2087                         new_fd = fd;
2088                 }
2089 
2090                 task_unlock(current);
2091 
2092                 if (new_cred) {
2093                         /* Install the new user namespace */
2094                         commit_creds(new_cred);
2095                         new_cred = NULL;
2096                 }
2097         }
2098 
2099 bad_unshare_cleanup_cred:
2100         if (new_cred)
2101                 put_cred(new_cred);
2102 bad_unshare_cleanup_fd:
2103         if (new_fd)
2104                 put_files_struct(new_fd);
2105 
2106 bad_unshare_cleanup_fs:
2107         if (new_fs)
2108                 free_fs_struct(new_fs);
2109 
2110 bad_unshare_out:
2111         return err;
2112 }
2113 
2114 /*
2115  *      Helper to unshare the files of the current task.
2116  *      We don't want to expose copy_files internals to
2117  *      the exec layer of the kernel.
2118  */
2119 
2120 int unshare_files(struct files_struct **displaced)
2121 {
2122         struct task_struct *task = current;
2123         struct files_struct *copy = NULL;
2124         int error;
2125 
2126         error = unshare_fd(CLONE_FILES, &copy);
2127         if (error || !copy) {
2128                 *displaced = NULL;
2129                 return error;
2130         }
2131         *displaced = task->files;
2132         task_lock(task);
2133         task->files = copy;
2134         task_unlock(task);
2135         return 0;
2136 }
2137 
2138 int sysctl_max_threads(struct ctl_table *table, int write,
2139                        void __user *buffer, size_t *lenp, loff_t *ppos)
2140 {
2141         struct ctl_table t;
2142         int ret;
2143         int threads = max_threads;
2144         int min = MIN_THREADS;
2145         int max = MAX_THREADS;
2146 
2147         t = *table;
2148         t.data = &threads;
2149         t.extra1 = &min;
2150         t.extra2 = &max;
2151 
2152         ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
2153         if (ret || !write)
2154                 return ret;
2155 
2156         set_max_threads(threads);
2157 
2158         return 0;
2159 }
2160 

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