Version:  2.0.40 2.2.26 2.4.37 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4

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

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