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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_pages_node(node, THREADINFO_GFP,
166                                              THREAD_SIZE_ORDER);
167 
168         return page ? page_address(page) : NULL;
169 }
170 
171 static inline void free_thread_stack(unsigned long *stack)
172 {
173         __free_pages(virt_to_page(stack), THREAD_SIZE_ORDER);
174 }
175 # else
176 static struct kmem_cache *thread_stack_cache;
177 
178 static unsigned long *alloc_thread_stack_node(struct task_struct *tsk,
179                                                   int node)
180 {
181         return kmem_cache_alloc_node(thread_stack_cache, THREADINFO_GFP, node);
182 }
183 
184 static void free_thread_stack(unsigned long *stack)
185 {
186         kmem_cache_free(thread_stack_cache, stack);
187 }
188 
189 void thread_stack_cache_init(void)
190 {
191         thread_stack_cache = kmem_cache_create("thread_stack", THREAD_SIZE,
192                                               THREAD_SIZE, 0, NULL);
193         BUG_ON(thread_stack_cache == NULL);
194 }
195 # endif
196 #endif
197 
198 /* SLAB cache for signal_struct structures (tsk->signal) */
199 static struct kmem_cache *signal_cachep;
200 
201 /* SLAB cache for sighand_struct structures (tsk->sighand) */
202 struct kmem_cache *sighand_cachep;
203 
204 /* SLAB cache for files_struct structures (tsk->files) */
205 struct kmem_cache *files_cachep;
206 
207 /* SLAB cache for fs_struct structures (tsk->fs) */
208 struct kmem_cache *fs_cachep;
209 
210 /* SLAB cache for vm_area_struct structures */
211 struct kmem_cache *vm_area_cachep;
212 
213 /* SLAB cache for mm_struct structures (tsk->mm) */
214 static struct kmem_cache *mm_cachep;
215 
216 static void account_kernel_stack(unsigned long *stack, int account)
217 {
218         /* All stack pages are in the same zone and belong to the same memcg. */
219         struct page *first_page = virt_to_page(stack);
220 
221         mod_zone_page_state(page_zone(first_page), NR_KERNEL_STACK_KB,
222                             THREAD_SIZE / 1024 * account);
223 
224         memcg_kmem_update_page_stat(
225                 first_page, MEMCG_KERNEL_STACK_KB,
226                 account * (THREAD_SIZE / 1024));
227 }
228 
229 void free_task(struct task_struct *tsk)
230 {
231         account_kernel_stack(tsk->stack, -1);
232         arch_release_thread_stack(tsk->stack);
233         free_thread_stack(tsk->stack);
234         rt_mutex_debug_task_free(tsk);
235         ftrace_graph_exit_task(tsk);
236         put_seccomp_filter(tsk);
237         arch_release_task_struct(tsk);
238         free_task_struct(tsk);
239 }
240 EXPORT_SYMBOL(free_task);
241 
242 static inline void free_signal_struct(struct signal_struct *sig)
243 {
244         taskstats_tgid_free(sig);
245         sched_autogroup_exit(sig);
246         kmem_cache_free(signal_cachep, sig);
247 }
248 
249 static inline void put_signal_struct(struct signal_struct *sig)
250 {
251         if (atomic_dec_and_test(&sig->sigcnt))
252                 free_signal_struct(sig);
253 }
254 
255 void __put_task_struct(struct task_struct *tsk)
256 {
257         WARN_ON(!tsk->exit_state);
258         WARN_ON(atomic_read(&tsk->usage));
259         WARN_ON(tsk == current);
260 
261         cgroup_free(tsk);
262         task_numa_free(tsk);
263         security_task_free(tsk);
264         exit_creds(tsk);
265         delayacct_tsk_free(tsk);
266         put_signal_struct(tsk->signal);
267 
268         if (!profile_handoff_task(tsk))
269                 free_task(tsk);
270 }
271 EXPORT_SYMBOL_GPL(__put_task_struct);
272 
273 void __init __weak arch_task_cache_init(void) { }
274 
275 /*
276  * set_max_threads
277  */
278 static void set_max_threads(unsigned int max_threads_suggested)
279 {
280         u64 threads;
281 
282         /*
283          * The number of threads shall be limited such that the thread
284          * structures may only consume a small part of the available memory.
285          */
286         if (fls64(totalram_pages) + fls64(PAGE_SIZE) > 64)
287                 threads = MAX_THREADS;
288         else
289                 threads = div64_u64((u64) totalram_pages * (u64) PAGE_SIZE,
290                                     (u64) THREAD_SIZE * 8UL);
291 
292         if (threads > max_threads_suggested)
293                 threads = max_threads_suggested;
294 
295         max_threads = clamp_t(u64, threads, MIN_THREADS, MAX_THREADS);
296 }
297 
298 #ifdef CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT
299 /* Initialized by the architecture: */
300 int arch_task_struct_size __read_mostly;
301 #endif
302 
303 void __init fork_init(void)
304 {
305 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
306 #ifndef ARCH_MIN_TASKALIGN
307 #define ARCH_MIN_TASKALIGN      L1_CACHE_BYTES
308 #endif
309         /* create a slab on which task_structs can be allocated */
310         task_struct_cachep = kmem_cache_create("task_struct",
311                         arch_task_struct_size, ARCH_MIN_TASKALIGN,
312                         SLAB_PANIC|SLAB_NOTRACK|SLAB_ACCOUNT, NULL);
313 #endif
314 
315         /* do the arch specific task caches init */
316         arch_task_cache_init();
317 
318         set_max_threads(MAX_THREADS);
319 
320         init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
321         init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
322         init_task.signal->rlim[RLIMIT_SIGPENDING] =
323                 init_task.signal->rlim[RLIMIT_NPROC];
324 }
325 
326 int __weak arch_dup_task_struct(struct task_struct *dst,
327                                                struct task_struct *src)
328 {
329         *dst = *src;
330         return 0;
331 }
332 
333 void set_task_stack_end_magic(struct task_struct *tsk)
334 {
335         unsigned long *stackend;
336 
337         stackend = end_of_stack(tsk);
338         *stackend = STACK_END_MAGIC;    /* for overflow detection */
339 }
340 
341 static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
342 {
343         struct task_struct *tsk;
344         unsigned long *stack;
345         int err;
346 
347         if (node == NUMA_NO_NODE)
348                 node = tsk_fork_get_node(orig);
349         tsk = alloc_task_struct_node(node);
350         if (!tsk)
351                 return NULL;
352 
353         stack = alloc_thread_stack_node(tsk, node);
354         if (!stack)
355                 goto free_tsk;
356 
357         err = arch_dup_task_struct(tsk, orig);
358         if (err)
359                 goto free_stack;
360 
361         tsk->stack = stack;
362 #ifdef CONFIG_SECCOMP
363         /*
364          * We must handle setting up seccomp filters once we're under
365          * the sighand lock in case orig has changed between now and
366          * then. Until then, filter must be NULL to avoid messing up
367          * the usage counts on the error path calling free_task.
368          */
369         tsk->seccomp.filter = NULL;
370 #endif
371 
372         setup_thread_stack(tsk, orig);
373         clear_user_return_notifier(tsk);
374         clear_tsk_need_resched(tsk);
375         set_task_stack_end_magic(tsk);
376 
377 #ifdef CONFIG_CC_STACKPROTECTOR
378         tsk->stack_canary = get_random_int();
379 #endif
380 
381         /*
382          * One for us, one for whoever does the "release_task()" (usually
383          * parent)
384          */
385         atomic_set(&tsk->usage, 2);
386 #ifdef CONFIG_BLK_DEV_IO_TRACE
387         tsk->btrace_seq = 0;
388 #endif
389         tsk->splice_pipe = NULL;
390         tsk->task_frag.page = NULL;
391         tsk->wake_q.next = NULL;
392 
393         account_kernel_stack(stack, 1);
394 
395         kcov_task_init(tsk);
396 
397         return tsk;
398 
399 free_stack:
400         free_thread_stack(stack);
401 free_tsk:
402         free_task_struct(tsk);
403         return NULL;
404 }
405 
406 #ifdef CONFIG_MMU
407 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
408 {
409         struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
410         struct rb_node **rb_link, *rb_parent;
411         int retval;
412         unsigned long charge;
413 
414         uprobe_start_dup_mmap();
415         if (down_write_killable(&oldmm->mmap_sem)) {
416                 retval = -EINTR;
417                 goto fail_uprobe_end;
418         }
419         flush_cache_dup_mm(oldmm);
420         uprobe_dup_mmap(oldmm, mm);
421         /*
422          * Not linked in yet - no deadlock potential:
423          */
424         down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
425 
426         /* No ordering required: file already has been exposed. */
427         RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
428 
429         mm->total_vm = oldmm->total_vm;
430         mm->data_vm = oldmm->data_vm;
431         mm->exec_vm = oldmm->exec_vm;
432         mm->stack_vm = oldmm->stack_vm;
433 
434         rb_link = &mm->mm_rb.rb_node;
435         rb_parent = NULL;
436         pprev = &mm->mmap;
437         retval = ksm_fork(mm, oldmm);
438         if (retval)
439                 goto out;
440         retval = khugepaged_fork(mm, oldmm);
441         if (retval)
442                 goto out;
443 
444         prev = NULL;
445         for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
446                 struct file *file;
447 
448                 if (mpnt->vm_flags & VM_DONTCOPY) {
449                         vm_stat_account(mm, mpnt->vm_flags, -vma_pages(mpnt));
450                         continue;
451                 }
452                 charge = 0;
453                 if (mpnt->vm_flags & VM_ACCOUNT) {
454                         unsigned long len = vma_pages(mpnt);
455 
456                         if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
457                                 goto fail_nomem;
458                         charge = len;
459                 }
460                 tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
461                 if (!tmp)
462                         goto fail_nomem;
463                 *tmp = *mpnt;
464                 INIT_LIST_HEAD(&tmp->anon_vma_chain);
465                 retval = vma_dup_policy(mpnt, tmp);
466                 if (retval)
467                         goto fail_nomem_policy;
468                 tmp->vm_mm = mm;
469                 if (anon_vma_fork(tmp, mpnt))
470                         goto fail_nomem_anon_vma_fork;
471                 tmp->vm_flags &=
472                         ~(VM_LOCKED|VM_LOCKONFAULT|VM_UFFD_MISSING|VM_UFFD_WP);
473                 tmp->vm_next = tmp->vm_prev = NULL;
474                 tmp->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
475                 file = tmp->vm_file;
476                 if (file) {
477                         struct inode *inode = file_inode(file);
478                         struct address_space *mapping = file->f_mapping;
479 
480                         get_file(file);
481                         if (tmp->vm_flags & VM_DENYWRITE)
482                                 atomic_dec(&inode->i_writecount);
483                         i_mmap_lock_write(mapping);
484                         if (tmp->vm_flags & VM_SHARED)
485                                 atomic_inc(&mapping->i_mmap_writable);
486                         flush_dcache_mmap_lock(mapping);
487                         /* insert tmp into the share list, just after mpnt */
488                         vma_interval_tree_insert_after(tmp, mpnt,
489                                         &mapping->i_mmap);
490                         flush_dcache_mmap_unlock(mapping);
491                         i_mmap_unlock_write(mapping);
492                 }
493 
494                 /*
495                  * Clear hugetlb-related page reserves for children. This only
496                  * affects MAP_PRIVATE mappings. Faults generated by the child
497                  * are not guaranteed to succeed, even if read-only
498                  */
499                 if (is_vm_hugetlb_page(tmp))
500                         reset_vma_resv_huge_pages(tmp);
501 
502                 /*
503                  * Link in the new vma and copy the page table entries.
504                  */
505                 *pprev = tmp;
506                 pprev = &tmp->vm_next;
507                 tmp->vm_prev = prev;
508                 prev = tmp;
509 
510                 __vma_link_rb(mm, tmp, rb_link, rb_parent);
511                 rb_link = &tmp->vm_rb.rb_right;
512                 rb_parent = &tmp->vm_rb;
513 
514                 mm->map_count++;
515                 retval = copy_page_range(mm, oldmm, mpnt);
516 
517                 if (tmp->vm_ops && tmp->vm_ops->open)
518                         tmp->vm_ops->open(tmp);
519 
520                 if (retval)
521                         goto out;
522         }
523         /* a new mm has just been created */
524         arch_dup_mmap(oldmm, mm);
525         retval = 0;
526 out:
527         up_write(&mm->mmap_sem);
528         flush_tlb_mm(oldmm);
529         up_write(&oldmm->mmap_sem);
530 fail_uprobe_end:
531         uprobe_end_dup_mmap();
532         return retval;
533 fail_nomem_anon_vma_fork:
534         mpol_put(vma_policy(tmp));
535 fail_nomem_policy:
536         kmem_cache_free(vm_area_cachep, tmp);
537 fail_nomem:
538         retval = -ENOMEM;
539         vm_unacct_memory(charge);
540         goto out;
541 }
542 
543 static inline int mm_alloc_pgd(struct mm_struct *mm)
544 {
545         mm->pgd = pgd_alloc(mm);
546         if (unlikely(!mm->pgd))
547                 return -ENOMEM;
548         return 0;
549 }
550 
551 static inline void mm_free_pgd(struct mm_struct *mm)
552 {
553         pgd_free(mm, mm->pgd);
554 }
555 #else
556 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
557 {
558         down_write(&oldmm->mmap_sem);
559         RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
560         up_write(&oldmm->mmap_sem);
561         return 0;
562 }
563 #define mm_alloc_pgd(mm)        (0)
564 #define mm_free_pgd(mm)
565 #endif /* CONFIG_MMU */
566 
567 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
568 
569 #define allocate_mm()   (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
570 #define free_mm(mm)     (kmem_cache_free(mm_cachep, (mm)))
571 
572 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
573 
574 static int __init coredump_filter_setup(char *s)
575 {
576         default_dump_filter =
577                 (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
578                 MMF_DUMP_FILTER_MASK;
579         return 1;
580 }
581 
582 __setup("coredump_filter=", coredump_filter_setup);
583 
584 #include <linux/init_task.h>
585 
586 static void mm_init_aio(struct mm_struct *mm)
587 {
588 #ifdef CONFIG_AIO
589         spin_lock_init(&mm->ioctx_lock);
590         mm->ioctx_table = NULL;
591 #endif
592 }
593 
594 static void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
595 {
596 #ifdef CONFIG_MEMCG
597         mm->owner = p;
598 #endif
599 }
600 
601 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
602 {
603         mm->mmap = NULL;
604         mm->mm_rb = RB_ROOT;
605         mm->vmacache_seqnum = 0;
606         atomic_set(&mm->mm_users, 1);
607         atomic_set(&mm->mm_count, 1);
608         init_rwsem(&mm->mmap_sem);
609         INIT_LIST_HEAD(&mm->mmlist);
610         mm->core_state = NULL;
611         atomic_long_set(&mm->nr_ptes, 0);
612         mm_nr_pmds_init(mm);
613         mm->map_count = 0;
614         mm->locked_vm = 0;
615         mm->pinned_vm = 0;
616         memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
617         spin_lock_init(&mm->page_table_lock);
618         mm_init_cpumask(mm);
619         mm_init_aio(mm);
620         mm_init_owner(mm, p);
621         mmu_notifier_mm_init(mm);
622         clear_tlb_flush_pending(mm);
623 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
624         mm->pmd_huge_pte = NULL;
625 #endif
626 
627         if (current->mm) {
628                 mm->flags = current->mm->flags & MMF_INIT_MASK;
629                 mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
630         } else {
631                 mm->flags = default_dump_filter;
632                 mm->def_flags = 0;
633         }
634 
635         if (mm_alloc_pgd(mm))
636                 goto fail_nopgd;
637 
638         if (init_new_context(p, mm))
639                 goto fail_nocontext;
640 
641         return mm;
642 
643 fail_nocontext:
644         mm_free_pgd(mm);
645 fail_nopgd:
646         free_mm(mm);
647         return NULL;
648 }
649 
650 static void check_mm(struct mm_struct *mm)
651 {
652         int i;
653 
654         for (i = 0; i < NR_MM_COUNTERS; i++) {
655                 long x = atomic_long_read(&mm->rss_stat.count[i]);
656 
657                 if (unlikely(x))
658                         printk(KERN_ALERT "BUG: Bad rss-counter state "
659                                           "mm:%p idx:%d val:%ld\n", mm, i, x);
660         }
661 
662         if (atomic_long_read(&mm->nr_ptes))
663                 pr_alert("BUG: non-zero nr_ptes on freeing mm: %ld\n",
664                                 atomic_long_read(&mm->nr_ptes));
665         if (mm_nr_pmds(mm))
666                 pr_alert("BUG: non-zero nr_pmds on freeing mm: %ld\n",
667                                 mm_nr_pmds(mm));
668 
669 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
670         VM_BUG_ON_MM(mm->pmd_huge_pte, mm);
671 #endif
672 }
673 
674 /*
675  * Allocate and initialize an mm_struct.
676  */
677 struct mm_struct *mm_alloc(void)
678 {
679         struct mm_struct *mm;
680 
681         mm = allocate_mm();
682         if (!mm)
683                 return NULL;
684 
685         memset(mm, 0, sizeof(*mm));
686         return mm_init(mm, current);
687 }
688 
689 /*
690  * Called when the last reference to the mm
691  * is dropped: either by a lazy thread or by
692  * mmput. Free the page directory and the mm.
693  */
694 void __mmdrop(struct mm_struct *mm)
695 {
696         BUG_ON(mm == &init_mm);
697         mm_free_pgd(mm);
698         destroy_context(mm);
699         mmu_notifier_mm_destroy(mm);
700         check_mm(mm);
701         free_mm(mm);
702 }
703 EXPORT_SYMBOL_GPL(__mmdrop);
704 
705 static inline void __mmput(struct mm_struct *mm)
706 {
707         VM_BUG_ON(atomic_read(&mm->mm_users));
708 
709         uprobe_clear_state(mm);
710         exit_aio(mm);
711         ksm_exit(mm);
712         khugepaged_exit(mm); /* must run before exit_mmap */
713         exit_mmap(mm);
714         set_mm_exe_file(mm, NULL);
715         if (!list_empty(&mm->mmlist)) {
716                 spin_lock(&mmlist_lock);
717                 list_del(&mm->mmlist);
718                 spin_unlock(&mmlist_lock);
719         }
720         if (mm->binfmt)
721                 module_put(mm->binfmt->module);
722         mmdrop(mm);
723 }
724 
725 /*
726  * Decrement the use count and release all resources for an mm.
727  */
728 void mmput(struct mm_struct *mm)
729 {
730         might_sleep();
731 
732         if (atomic_dec_and_test(&mm->mm_users))
733                 __mmput(mm);
734 }
735 EXPORT_SYMBOL_GPL(mmput);
736 
737 #ifdef CONFIG_MMU
738 static void mmput_async_fn(struct work_struct *work)
739 {
740         struct mm_struct *mm = container_of(work, struct mm_struct, async_put_work);
741         __mmput(mm);
742 }
743 
744 void mmput_async(struct mm_struct *mm)
745 {
746         if (atomic_dec_and_test(&mm->mm_users)) {
747                 INIT_WORK(&mm->async_put_work, mmput_async_fn);
748                 schedule_work(&mm->async_put_work);
749         }
750 }
751 #endif
752 
753 /**
754  * set_mm_exe_file - change a reference to the mm's executable file
755  *
756  * This changes mm's executable file (shown as symlink /proc/[pid]/exe).
757  *
758  * Main users are mmput() and sys_execve(). Callers prevent concurrent
759  * invocations: in mmput() nobody alive left, in execve task is single
760  * threaded. sys_prctl(PR_SET_MM_MAP/EXE_FILE) also needs to set the
761  * mm->exe_file, but does so without using set_mm_exe_file() in order
762  * to do avoid the need for any locks.
763  */
764 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
765 {
766         struct file *old_exe_file;
767 
768         /*
769          * It is safe to dereference the exe_file without RCU as
770          * this function is only called if nobody else can access
771          * this mm -- see comment above for justification.
772          */
773         old_exe_file = rcu_dereference_raw(mm->exe_file);
774 
775         if (new_exe_file)
776                 get_file(new_exe_file);
777         rcu_assign_pointer(mm->exe_file, new_exe_file);
778         if (old_exe_file)
779                 fput(old_exe_file);
780 }
781 
782 /**
783  * get_mm_exe_file - acquire a reference to the mm's executable file
784  *
785  * Returns %NULL if mm has no associated executable file.
786  * User must release file via fput().
787  */
788 struct file *get_mm_exe_file(struct mm_struct *mm)
789 {
790         struct file *exe_file;
791 
792         rcu_read_lock();
793         exe_file = rcu_dereference(mm->exe_file);
794         if (exe_file && !get_file_rcu(exe_file))
795                 exe_file = NULL;
796         rcu_read_unlock();
797         return exe_file;
798 }
799 EXPORT_SYMBOL(get_mm_exe_file);
800 
801 /**
802  * get_task_exe_file - acquire a reference to the task's executable file
803  *
804  * Returns %NULL if task's mm (if any) has no associated executable file or
805  * this is a kernel thread with borrowed mm (see the comment above get_task_mm).
806  * User must release file via fput().
807  */
808 struct file *get_task_exe_file(struct task_struct *task)
809 {
810         struct file *exe_file = NULL;
811         struct mm_struct *mm;
812 
813         task_lock(task);
814         mm = task->mm;
815         if (mm) {
816                 if (!(task->flags & PF_KTHREAD))
817                         exe_file = get_mm_exe_file(mm);
818         }
819         task_unlock(task);
820         return exe_file;
821 }
822 EXPORT_SYMBOL(get_task_exe_file);
823 
824 /**
825  * get_task_mm - acquire a reference to the task's mm
826  *
827  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
828  * this kernel workthread has transiently adopted a user mm with use_mm,
829  * to do its AIO) is not set and if so returns a reference to it, after
830  * bumping up the use count.  User must release the mm via mmput()
831  * after use.  Typically used by /proc and ptrace.
832  */
833 struct mm_struct *get_task_mm(struct task_struct *task)
834 {
835         struct mm_struct *mm;
836 
837         task_lock(task);
838         mm = task->mm;
839         if (mm) {
840                 if (task->flags & PF_KTHREAD)
841                         mm = NULL;
842                 else
843                         atomic_inc(&mm->mm_users);
844         }
845         task_unlock(task);
846         return mm;
847 }
848 EXPORT_SYMBOL_GPL(get_task_mm);
849 
850 struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
851 {
852         struct mm_struct *mm;
853         int err;
854 
855         err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
856         if (err)
857                 return ERR_PTR(err);
858 
859         mm = get_task_mm(task);
860         if (mm && mm != current->mm &&
861                         !ptrace_may_access(task, mode)) {
862                 mmput(mm);
863                 mm = ERR_PTR(-EACCES);
864         }
865         mutex_unlock(&task->signal->cred_guard_mutex);
866 
867         return mm;
868 }
869 
870 static void complete_vfork_done(struct task_struct *tsk)
871 {
872         struct completion *vfork;
873 
874         task_lock(tsk);
875         vfork = tsk->vfork_done;
876         if (likely(vfork)) {
877                 tsk->vfork_done = NULL;
878                 complete(vfork);
879         }
880         task_unlock(tsk);
881 }
882 
883 static int wait_for_vfork_done(struct task_struct *child,
884                                 struct completion *vfork)
885 {
886         int killed;
887 
888         freezer_do_not_count();
889         killed = wait_for_completion_killable(vfork);
890         freezer_count();
891 
892         if (killed) {
893                 task_lock(child);
894                 child->vfork_done = NULL;
895                 task_unlock(child);
896         }
897 
898         put_task_struct(child);
899         return killed;
900 }
901 
902 /* Please note the differences between mmput and mm_release.
903  * mmput is called whenever we stop holding onto a mm_struct,
904  * error success whatever.
905  *
906  * mm_release is called after a mm_struct has been removed
907  * from the current process.
908  *
909  * This difference is important for error handling, when we
910  * only half set up a mm_struct for a new process and need to restore
911  * the old one.  Because we mmput the new mm_struct before
912  * restoring the old one. . .
913  * Eric Biederman 10 January 1998
914  */
915 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
916 {
917         /* Get rid of any futexes when releasing the mm */
918 #ifdef CONFIG_FUTEX
919         if (unlikely(tsk->robust_list)) {
920                 exit_robust_list(tsk);
921                 tsk->robust_list = NULL;
922         }
923 #ifdef CONFIG_COMPAT
924         if (unlikely(tsk->compat_robust_list)) {
925                 compat_exit_robust_list(tsk);
926                 tsk->compat_robust_list = NULL;
927         }
928 #endif
929         if (unlikely(!list_empty(&tsk->pi_state_list)))
930                 exit_pi_state_list(tsk);
931 #endif
932 
933         uprobe_free_utask(tsk);
934 
935         /* Get rid of any cached register state */
936         deactivate_mm(tsk, mm);
937 
938         /*
939          * Signal userspace if we're not exiting with a core dump
940          * because we want to leave the value intact for debugging
941          * purposes.
942          */
943         if (tsk->clear_child_tid) {
944                 if (!(tsk->signal->flags & SIGNAL_GROUP_COREDUMP) &&
945                     atomic_read(&mm->mm_users) > 1) {
946                         /*
947                          * We don't check the error code - if userspace has
948                          * not set up a proper pointer then tough luck.
949                          */
950                         put_user(0, tsk->clear_child_tid);
951                         sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
952                                         1, NULL, NULL, 0);
953                 }
954                 tsk->clear_child_tid = NULL;
955         }
956 
957         /*
958          * All done, finally we can wake up parent and return this mm to him.
959          * Also kthread_stop() uses this completion for synchronization.
960          */
961         if (tsk->vfork_done)
962                 complete_vfork_done(tsk);
963 }
964 
965 /*
966  * Allocate a new mm structure and copy contents from the
967  * mm structure of the passed in task structure.
968  */
969 static struct mm_struct *dup_mm(struct task_struct *tsk)
970 {
971         struct mm_struct *mm, *oldmm = current->mm;
972         int err;
973 
974         mm = allocate_mm();
975         if (!mm)
976                 goto fail_nomem;
977 
978         memcpy(mm, oldmm, sizeof(*mm));
979 
980         if (!mm_init(mm, tsk))
981                 goto fail_nomem;
982 
983         err = dup_mmap(mm, oldmm);
984         if (err)
985                 goto free_pt;
986 
987         mm->hiwater_rss = get_mm_rss(mm);
988         mm->hiwater_vm = mm->total_vm;
989 
990         if (mm->binfmt && !try_module_get(mm->binfmt->module))
991                 goto free_pt;
992 
993         return mm;
994 
995 free_pt:
996         /* don't put binfmt in mmput, we haven't got module yet */
997         mm->binfmt = NULL;
998         mmput(mm);
999 
1000 fail_nomem:
1001         return NULL;
1002 }
1003 
1004 static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
1005 {
1006         struct mm_struct *mm, *oldmm;
1007         int retval;
1008 
1009         tsk->min_flt = tsk->maj_flt = 0;
1010         tsk->nvcsw = tsk->nivcsw = 0;
1011 #ifdef CONFIG_DETECT_HUNG_TASK
1012         tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
1013 #endif
1014 
1015         tsk->mm = NULL;
1016         tsk->active_mm = NULL;
1017 
1018         /*
1019          * Are we cloning a kernel thread?
1020          *
1021          * We need to steal a active VM for that..
1022          */
1023         oldmm = current->mm;
1024         if (!oldmm)
1025                 return 0;
1026 
1027         /* initialize the new vmacache entries */
1028         vmacache_flush(tsk);
1029 
1030         if (clone_flags & CLONE_VM) {
1031                 atomic_inc(&oldmm->mm_users);
1032                 mm = oldmm;
1033                 goto good_mm;
1034         }
1035 
1036         retval = -ENOMEM;
1037         mm = dup_mm(tsk);
1038         if (!mm)
1039                 goto fail_nomem;
1040 
1041 good_mm:
1042         tsk->mm = mm;
1043         tsk->active_mm = mm;
1044         return 0;
1045 
1046 fail_nomem:
1047         return retval;
1048 }
1049 
1050 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
1051 {
1052         struct fs_struct *fs = current->fs;
1053         if (clone_flags & CLONE_FS) {
1054                 /* tsk->fs is already what we want */
1055                 spin_lock(&fs->lock);
1056                 if (fs->in_exec) {
1057                         spin_unlock(&fs->lock);
1058                         return -EAGAIN;
1059                 }
1060                 fs->users++;
1061                 spin_unlock(&fs->lock);
1062                 return 0;
1063         }
1064         tsk->fs = copy_fs_struct(fs);
1065         if (!tsk->fs)
1066                 return -ENOMEM;
1067         return 0;
1068 }
1069 
1070 static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
1071 {
1072         struct files_struct *oldf, *newf;
1073         int error = 0;
1074 
1075         /*
1076          * A background process may not have any files ...
1077          */
1078         oldf = current->files;
1079         if (!oldf)
1080                 goto out;
1081 
1082         if (clone_flags & CLONE_FILES) {
1083                 atomic_inc(&oldf->count);
1084                 goto out;
1085         }
1086 
1087         newf = dup_fd(oldf, &error);
1088         if (!newf)
1089                 goto out;
1090 
1091         tsk->files = newf;
1092         error = 0;
1093 out:
1094         return error;
1095 }
1096 
1097 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
1098 {
1099 #ifdef CONFIG_BLOCK
1100         struct io_context *ioc = current->io_context;
1101         struct io_context *new_ioc;
1102 
1103         if (!ioc)
1104                 return 0;
1105         /*
1106          * Share io context with parent, if CLONE_IO is set
1107          */
1108         if (clone_flags & CLONE_IO) {
1109                 ioc_task_link(ioc);
1110                 tsk->io_context = ioc;
1111         } else if (ioprio_valid(ioc->ioprio)) {
1112                 new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
1113                 if (unlikely(!new_ioc))
1114                         return -ENOMEM;
1115 
1116                 new_ioc->ioprio = ioc->ioprio;
1117                 put_io_context(new_ioc);
1118         }
1119 #endif
1120         return 0;
1121 }
1122 
1123 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
1124 {
1125         struct sighand_struct *sig;
1126 
1127         if (clone_flags & CLONE_SIGHAND) {
1128                 atomic_inc(&current->sighand->count);
1129                 return 0;
1130         }
1131         sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
1132         rcu_assign_pointer(tsk->sighand, sig);
1133         if (!sig)
1134                 return -ENOMEM;
1135 
1136         atomic_set(&sig->count, 1);
1137         memcpy(sig->action, current->sighand->action, sizeof(sig->action));
1138         return 0;
1139 }
1140 
1141 void __cleanup_sighand(struct sighand_struct *sighand)
1142 {
1143         if (atomic_dec_and_test(&sighand->count)) {
1144                 signalfd_cleanup(sighand);
1145                 /*
1146                  * sighand_cachep is SLAB_DESTROY_BY_RCU so we can free it
1147                  * without an RCU grace period, see __lock_task_sighand().
1148                  */
1149                 kmem_cache_free(sighand_cachep, sighand);
1150         }
1151 }
1152 
1153 /*
1154  * Initialize POSIX timer handling for a thread group.
1155  */
1156 static void posix_cpu_timers_init_group(struct signal_struct *sig)
1157 {
1158         unsigned long cpu_limit;
1159 
1160         cpu_limit = READ_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1161         if (cpu_limit != RLIM_INFINITY) {
1162                 sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
1163                 sig->cputimer.running = true;
1164         }
1165 
1166         /* The timer lists. */
1167         INIT_LIST_HEAD(&sig->cpu_timers[0]);
1168         INIT_LIST_HEAD(&sig->cpu_timers[1]);
1169         INIT_LIST_HEAD(&sig->cpu_timers[2]);
1170 }
1171 
1172 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1173 {
1174         struct signal_struct *sig;
1175 
1176         if (clone_flags & CLONE_THREAD)
1177                 return 0;
1178 
1179         sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1180         tsk->signal = sig;
1181         if (!sig)
1182                 return -ENOMEM;
1183 
1184         sig->nr_threads = 1;
1185         atomic_set(&sig->live, 1);
1186         atomic_set(&sig->sigcnt, 1);
1187 
1188         /* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */
1189         sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node);
1190         tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);
1191 
1192         init_waitqueue_head(&sig->wait_chldexit);
1193         sig->curr_target = tsk;
1194         init_sigpending(&sig->shared_pending);
1195         INIT_LIST_HEAD(&sig->posix_timers);
1196         seqlock_init(&sig->stats_lock);
1197         prev_cputime_init(&sig->prev_cputime);
1198 
1199         hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1200         sig->real_timer.function = it_real_fn;
1201 
1202         task_lock(current->group_leader);
1203         memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1204         task_unlock(current->group_leader);
1205 
1206         posix_cpu_timers_init_group(sig);
1207 
1208         tty_audit_fork(sig);
1209         sched_autogroup_fork(sig);
1210 
1211         sig->oom_score_adj = current->signal->oom_score_adj;
1212         sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1213 
1214         sig->has_child_subreaper = current->signal->has_child_subreaper ||
1215                                    current->signal->is_child_subreaper;
1216 
1217         mutex_init(&sig->cred_guard_mutex);
1218 
1219         return 0;
1220 }
1221 
1222 static void copy_seccomp(struct task_struct *p)
1223 {
1224 #ifdef CONFIG_SECCOMP
1225         /*
1226          * Must be called with sighand->lock held, which is common to
1227          * all threads in the group. Holding cred_guard_mutex is not
1228          * needed because this new task is not yet running and cannot
1229          * be racing exec.
1230          */
1231         assert_spin_locked(&current->sighand->siglock);
1232 
1233         /* Ref-count the new filter user, and assign it. */
1234         get_seccomp_filter(current);
1235         p->seccomp = current->seccomp;
1236 
1237         /*
1238          * Explicitly enable no_new_privs here in case it got set
1239          * between the task_struct being duplicated and holding the
1240          * sighand lock. The seccomp state and nnp must be in sync.
1241          */
1242         if (task_no_new_privs(current))
1243                 task_set_no_new_privs(p);
1244 
1245         /*
1246          * If the parent gained a seccomp mode after copying thread
1247          * flags and between before we held the sighand lock, we have
1248          * to manually enable the seccomp thread flag here.
1249          */
1250         if (p->seccomp.mode != SECCOMP_MODE_DISABLED)
1251                 set_tsk_thread_flag(p, TIF_SECCOMP);
1252 #endif
1253 }
1254 
1255 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1256 {
1257         current->clear_child_tid = tidptr;
1258 
1259         return task_pid_vnr(current);
1260 }
1261 
1262 static void rt_mutex_init_task(struct task_struct *p)
1263 {
1264         raw_spin_lock_init(&p->pi_lock);
1265 #ifdef CONFIG_RT_MUTEXES
1266         p->pi_waiters = RB_ROOT;
1267         p->pi_waiters_leftmost = NULL;
1268         p->pi_blocked_on = NULL;
1269 #endif
1270 }
1271 
1272 /*
1273  * Initialize POSIX timer handling for a single task.
1274  */
1275 static void posix_cpu_timers_init(struct task_struct *tsk)
1276 {
1277         tsk->cputime_expires.prof_exp = 0;
1278         tsk->cputime_expires.virt_exp = 0;
1279         tsk->cputime_expires.sched_exp = 0;
1280         INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1281         INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1282         INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1283 }
1284 
1285 static inline void
1286 init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
1287 {
1288          task->pids[type].pid = pid;
1289 }
1290 
1291 /*
1292  * This creates a new process as a copy of the old one,
1293  * but does not actually start it yet.
1294  *
1295  * It copies the registers, and all the appropriate
1296  * parts of the process environment (as per the clone
1297  * flags). The actual kick-off is left to the caller.
1298  */
1299 static struct task_struct *copy_process(unsigned long clone_flags,
1300                                         unsigned long stack_start,
1301                                         unsigned long stack_size,
1302                                         int __user *child_tidptr,
1303                                         struct pid *pid,
1304                                         int trace,
1305                                         unsigned long tls,
1306                                         int node)
1307 {
1308         int retval;
1309         struct task_struct *p;
1310 
1311         if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1312                 return ERR_PTR(-EINVAL);
1313 
1314         if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
1315                 return ERR_PTR(-EINVAL);
1316 
1317         /*
1318          * Thread groups must share signals as well, and detached threads
1319          * can only be started up within the thread group.
1320          */
1321         if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1322                 return ERR_PTR(-EINVAL);
1323 
1324         /*
1325          * Shared signal handlers imply shared VM. By way of the above,
1326          * thread groups also imply shared VM. Blocking this case allows
1327          * for various simplifications in other code.
1328          */
1329         if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1330                 return ERR_PTR(-EINVAL);
1331 
1332         /*
1333          * Siblings of global init remain as zombies on exit since they are
1334          * not reaped by their parent (swapper). To solve this and to avoid
1335          * multi-rooted process trees, prevent global and container-inits
1336          * from creating siblings.
1337          */
1338         if ((clone_flags & CLONE_PARENT) &&
1339                                 current->signal->flags & SIGNAL_UNKILLABLE)
1340                 return ERR_PTR(-EINVAL);
1341 
1342         /*
1343          * If the new process will be in a different pid or user namespace
1344          * do not allow it to share a thread group with the forking task.
1345          */
1346         if (clone_flags & CLONE_THREAD) {
1347                 if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
1348                     (task_active_pid_ns(current) !=
1349                                 current->nsproxy->pid_ns_for_children))
1350                         return ERR_PTR(-EINVAL);
1351         }
1352 
1353         retval = security_task_create(clone_flags);
1354         if (retval)
1355                 goto fork_out;
1356 
1357         retval = -ENOMEM;
1358         p = dup_task_struct(current, node);
1359         if (!p)
1360                 goto fork_out;
1361 
1362         ftrace_graph_init_task(p);
1363 
1364         rt_mutex_init_task(p);
1365 
1366 #ifdef CONFIG_PROVE_LOCKING
1367         DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1368         DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1369 #endif
1370         retval = -EAGAIN;
1371         if (atomic_read(&p->real_cred->user->processes) >=
1372                         task_rlimit(p, RLIMIT_NPROC)) {
1373                 if (p->real_cred->user != INIT_USER &&
1374                     !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
1375                         goto bad_fork_free;
1376         }
1377         current->flags &= ~PF_NPROC_EXCEEDED;
1378 
1379         retval = copy_creds(p, clone_flags);
1380         if (retval < 0)
1381                 goto bad_fork_free;
1382 
1383         /*
1384          * If multiple threads are within copy_process(), then this check
1385          * triggers too late. This doesn't hurt, the check is only there
1386          * to stop root fork bombs.
1387          */
1388         retval = -EAGAIN;
1389         if (nr_threads >= max_threads)
1390                 goto bad_fork_cleanup_count;
1391 
1392         delayacct_tsk_init(p);  /* Must remain after dup_task_struct() */
1393         p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
1394         p->flags |= PF_FORKNOEXEC;
1395         INIT_LIST_HEAD(&p->children);
1396         INIT_LIST_HEAD(&p->sibling);
1397         rcu_copy_process(p);
1398         p->vfork_done = NULL;
1399         spin_lock_init(&p->alloc_lock);
1400 
1401         init_sigpending(&p->pending);
1402 
1403         p->utime = p->stime = p->gtime = 0;
1404         p->utimescaled = p->stimescaled = 0;
1405         prev_cputime_init(&p->prev_cputime);
1406 
1407 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
1408         seqcount_init(&p->vtime_seqcount);
1409         p->vtime_snap = 0;
1410         p->vtime_snap_whence = VTIME_INACTIVE;
1411 #endif
1412 
1413 #if defined(SPLIT_RSS_COUNTING)
1414         memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1415 #endif
1416 
1417         p->default_timer_slack_ns = current->timer_slack_ns;
1418 
1419         task_io_accounting_init(&p->ioac);
1420         acct_clear_integrals(p);
1421 
1422         posix_cpu_timers_init(p);
1423 
1424         p->start_time = ktime_get_ns();
1425         p->real_start_time = ktime_get_boot_ns();
1426         p->io_context = NULL;
1427         p->audit_context = NULL;
1428         cgroup_fork(p);
1429 #ifdef CONFIG_NUMA
1430         p->mempolicy = mpol_dup(p->mempolicy);
1431         if (IS_ERR(p->mempolicy)) {
1432                 retval = PTR_ERR(p->mempolicy);
1433                 p->mempolicy = NULL;
1434                 goto bad_fork_cleanup_threadgroup_lock;
1435         }
1436 #endif
1437 #ifdef CONFIG_CPUSETS
1438         p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
1439         p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
1440         seqcount_init(&p->mems_allowed_seq);
1441 #endif
1442 #ifdef CONFIG_TRACE_IRQFLAGS
1443         p->irq_events = 0;
1444         p->hardirqs_enabled = 0;
1445         p->hardirq_enable_ip = 0;
1446         p->hardirq_enable_event = 0;
1447         p->hardirq_disable_ip = _THIS_IP_;
1448         p->hardirq_disable_event = 0;
1449         p->softirqs_enabled = 1;
1450         p->softirq_enable_ip = _THIS_IP_;
1451         p->softirq_enable_event = 0;
1452         p->softirq_disable_ip = 0;
1453         p->softirq_disable_event = 0;
1454         p->hardirq_context = 0;
1455         p->softirq_context = 0;
1456 #endif
1457 
1458         p->pagefault_disabled = 0;
1459 
1460 #ifdef CONFIG_LOCKDEP
1461         p->lockdep_depth = 0; /* no locks held yet */
1462         p->curr_chain_key = 0;
1463         p->lockdep_recursion = 0;
1464 #endif
1465 
1466 #ifdef CONFIG_DEBUG_MUTEXES
1467         p->blocked_on = NULL; /* not blocked yet */
1468 #endif
1469 #ifdef CONFIG_BCACHE
1470         p->sequential_io        = 0;
1471         p->sequential_io_avg    = 0;
1472 #endif
1473 
1474         /* Perform scheduler related setup. Assign this task to a CPU. */
1475         retval = sched_fork(clone_flags, p);
1476         if (retval)
1477                 goto bad_fork_cleanup_policy;
1478 
1479         retval = perf_event_init_task(p);
1480         if (retval)
1481                 goto bad_fork_cleanup_policy;
1482         retval = audit_alloc(p);
1483         if (retval)
1484                 goto bad_fork_cleanup_perf;
1485         /* copy all the process information */
1486         shm_init_task(p);
1487         retval = copy_semundo(clone_flags, p);
1488         if (retval)
1489                 goto bad_fork_cleanup_audit;
1490         retval = copy_files(clone_flags, p);
1491         if (retval)
1492                 goto bad_fork_cleanup_semundo;
1493         retval = copy_fs(clone_flags, p);
1494         if (retval)
1495                 goto bad_fork_cleanup_files;
1496         retval = copy_sighand(clone_flags, p);
1497         if (retval)
1498                 goto bad_fork_cleanup_fs;
1499         retval = copy_signal(clone_flags, p);
1500         if (retval)
1501                 goto bad_fork_cleanup_sighand;
1502         retval = copy_mm(clone_flags, p);
1503         if (retval)
1504                 goto bad_fork_cleanup_signal;
1505         retval = copy_namespaces(clone_flags, p);
1506         if (retval)
1507                 goto bad_fork_cleanup_mm;
1508         retval = copy_io(clone_flags, p);
1509         if (retval)
1510                 goto bad_fork_cleanup_namespaces;
1511         retval = copy_thread_tls(clone_flags, stack_start, stack_size, p, tls);
1512         if (retval)
1513                 goto bad_fork_cleanup_io;
1514 
1515         if (pid != &init_struct_pid) {
1516                 pid = alloc_pid(p->nsproxy->pid_ns_for_children);
1517                 if (IS_ERR(pid)) {
1518                         retval = PTR_ERR(pid);
1519                         goto bad_fork_cleanup_thread;
1520                 }
1521         }
1522 
1523         p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1524         /*
1525          * Clear TID on mm_release()?
1526          */
1527         p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
1528 #ifdef CONFIG_BLOCK
1529         p->plug = NULL;
1530 #endif
1531 #ifdef CONFIG_FUTEX
1532         p->robust_list = NULL;
1533 #ifdef CONFIG_COMPAT
1534         p->compat_robust_list = NULL;
1535 #endif
1536         INIT_LIST_HEAD(&p->pi_state_list);
1537         p->pi_state_cache = NULL;
1538 #endif
1539         /*
1540          * sigaltstack should be cleared when sharing the same VM
1541          */
1542         if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1543                 sas_ss_reset(p);
1544 
1545         /*
1546          * Syscall tracing and stepping should be turned off in the
1547          * child regardless of CLONE_PTRACE.
1548          */
1549         user_disable_single_step(p);
1550         clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1551 #ifdef TIF_SYSCALL_EMU
1552         clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1553 #endif
1554         clear_all_latency_tracing(p);
1555 
1556         /* ok, now we should be set up.. */
1557         p->pid = pid_nr(pid);
1558         if (clone_flags & CLONE_THREAD) {
1559                 p->exit_signal = -1;
1560                 p->group_leader = current->group_leader;
1561                 p->tgid = current->tgid;
1562         } else {
1563                 if (clone_flags & CLONE_PARENT)
1564                         p->exit_signal = current->group_leader->exit_signal;
1565                 else
1566                         p->exit_signal = (clone_flags & CSIGNAL);
1567                 p->group_leader = p;
1568                 p->tgid = p->pid;
1569         }
1570 
1571         p->nr_dirtied = 0;
1572         p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
1573         p->dirty_paused_when = 0;
1574 
1575         p->pdeath_signal = 0;
1576         INIT_LIST_HEAD(&p->thread_group);
1577         p->task_works = NULL;
1578 
1579         threadgroup_change_begin(current);
1580         /*
1581          * Ensure that the cgroup subsystem policies allow the new process to be
1582          * forked. It should be noted the the new process's css_set can be changed
1583          * between here and cgroup_post_fork() if an organisation operation is in
1584          * progress.
1585          */
1586         retval = cgroup_can_fork(p);
1587         if (retval)
1588                 goto bad_fork_free_pid;
1589 
1590         /*
1591          * Make it visible to the rest of the system, but dont wake it up yet.
1592          * Need tasklist lock for parent etc handling!
1593          */
1594         write_lock_irq(&tasklist_lock);
1595 
1596         /* CLONE_PARENT re-uses the old parent */
1597         if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1598                 p->real_parent = current->real_parent;
1599                 p->parent_exec_id = current->parent_exec_id;
1600         } else {
1601                 p->real_parent = current;
1602                 p->parent_exec_id = current->self_exec_id;
1603         }
1604 
1605         spin_lock(&current->sighand->siglock);
1606 
1607         /*
1608          * Copy seccomp details explicitly here, in case they were changed
1609          * before holding sighand lock.
1610          */
1611         copy_seccomp(p);
1612 
1613         /*
1614          * Process group and session signals need to be delivered to just the
1615          * parent before the fork or both the parent and the child after the
1616          * fork. Restart if a signal comes in before we add the new process to
1617          * it's process group.
1618          * A fatal signal pending means that current will exit, so the new
1619          * thread can't slip out of an OOM kill (or normal SIGKILL).
1620         */
1621         recalc_sigpending();
1622         if (signal_pending(current)) {
1623                 spin_unlock(&current->sighand->siglock);
1624                 write_unlock_irq(&tasklist_lock);
1625                 retval = -ERESTARTNOINTR;
1626                 goto bad_fork_cancel_cgroup;
1627         }
1628 
1629         if (likely(p->pid)) {
1630                 ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
1631 
1632                 init_task_pid(p, PIDTYPE_PID, pid);
1633                 if (thread_group_leader(p)) {
1634                         init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
1635                         init_task_pid(p, PIDTYPE_SID, task_session(current));
1636 
1637                         if (is_child_reaper(pid)) {
1638                                 ns_of_pid(pid)->child_reaper = p;
1639                                 p->signal->flags |= SIGNAL_UNKILLABLE;
1640                         }
1641 
1642                         p->signal->leader_pid = pid;
1643                         p->signal->tty = tty_kref_get(current->signal->tty);
1644                         list_add_tail(&p->sibling, &p->real_parent->children);
1645                         list_add_tail_rcu(&p->tasks, &init_task.tasks);
1646                         attach_pid(p, PIDTYPE_PGID);
1647                         attach_pid(p, PIDTYPE_SID);
1648                         __this_cpu_inc(process_counts);
1649                 } else {
1650                         current->signal->nr_threads++;
1651                         atomic_inc(&current->signal->live);
1652                         atomic_inc(&current->signal->sigcnt);
1653                         list_add_tail_rcu(&p->thread_group,
1654                                           &p->group_leader->thread_group);
1655                         list_add_tail_rcu(&p->thread_node,
1656                                           &p->signal->thread_head);
1657                 }
1658                 attach_pid(p, PIDTYPE_PID);
1659                 nr_threads++;
1660         }
1661 
1662         total_forks++;
1663         spin_unlock(&current->sighand->siglock);
1664         syscall_tracepoint_update(p);
1665         write_unlock_irq(&tasklist_lock);
1666 
1667         proc_fork_connector(p);
1668         cgroup_post_fork(p);
1669         threadgroup_change_end(current);
1670         perf_event_fork(p);
1671 
1672         trace_task_newtask(p, clone_flags);
1673         uprobe_copy_process(p, clone_flags);
1674 
1675         return p;
1676 
1677 bad_fork_cancel_cgroup:
1678         cgroup_cancel_fork(p);
1679 bad_fork_free_pid:
1680         threadgroup_change_end(current);
1681         if (pid != &init_struct_pid)
1682                 free_pid(pid);
1683 bad_fork_cleanup_thread:
1684         exit_thread(p);
1685 bad_fork_cleanup_io:
1686         if (p->io_context)
1687                 exit_io_context(p);
1688 bad_fork_cleanup_namespaces:
1689         exit_task_namespaces(p);
1690 bad_fork_cleanup_mm:
1691         if (p->mm)
1692                 mmput(p->mm);
1693 bad_fork_cleanup_signal:
1694         if (!(clone_flags & CLONE_THREAD))
1695                 free_signal_struct(p->signal);
1696 bad_fork_cleanup_sighand:
1697         __cleanup_sighand(p->sighand);
1698 bad_fork_cleanup_fs:
1699         exit_fs(p); /* blocking */
1700 bad_fork_cleanup_files:
1701         exit_files(p); /* blocking */
1702 bad_fork_cleanup_semundo:
1703         exit_sem(p);
1704 bad_fork_cleanup_audit:
1705         audit_free(p);
1706 bad_fork_cleanup_perf:
1707         perf_event_free_task(p);
1708 bad_fork_cleanup_policy:
1709 #ifdef CONFIG_NUMA
1710         mpol_put(p->mempolicy);
1711 bad_fork_cleanup_threadgroup_lock:
1712 #endif
1713         delayacct_tsk_free(p);
1714 bad_fork_cleanup_count:
1715         atomic_dec(&p->cred->user->processes);
1716         exit_creds(p);
1717 bad_fork_free:
1718         free_task(p);
1719 fork_out:
1720         return ERR_PTR(retval);
1721 }
1722 
1723 static inline void init_idle_pids(struct pid_link *links)
1724 {
1725         enum pid_type type;
1726 
1727         for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1728                 INIT_HLIST_NODE(&links[type].node); /* not really needed */
1729                 links[type].pid = &init_struct_pid;
1730         }
1731 }
1732 
1733 struct task_struct *fork_idle(int cpu)
1734 {
1735         struct task_struct *task;
1736         task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0, 0,
1737                             cpu_to_node(cpu));
1738         if (!IS_ERR(task)) {
1739                 init_idle_pids(task->pids);
1740                 init_idle(task, cpu);
1741         }
1742 
1743         return task;
1744 }
1745 
1746 /*
1747  *  Ok, this is the main fork-routine.
1748  *
1749  * It copies the process, and if successful kick-starts
1750  * it and waits for it to finish using the VM if required.
1751  */
1752 long _do_fork(unsigned long clone_flags,
1753               unsigned long stack_start,
1754               unsigned long stack_size,
1755               int __user *parent_tidptr,
1756               int __user *child_tidptr,
1757               unsigned long tls)
1758 {
1759         struct task_struct *p;
1760         int trace = 0;
1761         long nr;
1762 
1763         /*
1764          * Determine whether and which event to report to ptracer.  When
1765          * called from kernel_thread or CLONE_UNTRACED is explicitly
1766          * requested, no event is reported; otherwise, report if the event
1767          * for the type of forking is enabled.
1768          */
1769         if (!(clone_flags & CLONE_UNTRACED)) {
1770                 if (clone_flags & CLONE_VFORK)
1771                         trace = PTRACE_EVENT_VFORK;
1772                 else if ((clone_flags & CSIGNAL) != SIGCHLD)
1773                         trace = PTRACE_EVENT_CLONE;
1774                 else
1775                         trace = PTRACE_EVENT_FORK;
1776 
1777                 if (likely(!ptrace_event_enabled(current, trace)))
1778                         trace = 0;
1779         }
1780 
1781         p = copy_process(clone_flags, stack_start, stack_size,
1782                          child_tidptr, NULL, trace, tls, NUMA_NO_NODE);
1783         /*
1784          * Do this prior waking up the new thread - the thread pointer
1785          * might get invalid after that point, if the thread exits quickly.
1786          */
1787         if (!IS_ERR(p)) {
1788                 struct completion vfork;
1789                 struct pid *pid;
1790 
1791                 trace_sched_process_fork(current, p);
1792 
1793                 pid = get_task_pid(p, PIDTYPE_PID);
1794                 nr = pid_vnr(pid);
1795 
1796                 if (clone_flags & CLONE_PARENT_SETTID)
1797                         put_user(nr, parent_tidptr);
1798 
1799                 if (clone_flags & CLONE_VFORK) {
1800                         p->vfork_done = &vfork;
1801                         init_completion(&vfork);
1802                         get_task_struct(p);
1803                 }
1804 
1805                 wake_up_new_task(p);
1806 
1807                 /* forking complete and child started to run, tell ptracer */
1808                 if (unlikely(trace))
1809                         ptrace_event_pid(trace, pid);
1810 
1811                 if (clone_flags & CLONE_VFORK) {
1812                         if (!wait_for_vfork_done(p, &vfork))
1813                                 ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
1814                 }
1815 
1816                 put_pid(pid);
1817         } else {
1818                 nr = PTR_ERR(p);
1819         }
1820         return nr;
1821 }
1822 
1823 #ifndef CONFIG_HAVE_COPY_THREAD_TLS
1824 /* For compatibility with architectures that call do_fork directly rather than
1825  * using the syscall entry points below. */
1826 long do_fork(unsigned long clone_flags,
1827               unsigned long stack_start,
1828               unsigned long stack_size,
1829               int __user *parent_tidptr,
1830               int __user *child_tidptr)
1831 {
1832         return _do_fork(clone_flags, stack_start, stack_size,
1833                         parent_tidptr, child_tidptr, 0);
1834 }
1835 #endif
1836 
1837 /*
1838  * Create a kernel thread.
1839  */
1840 pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
1841 {
1842         return _do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
1843                 (unsigned long)arg, NULL, NULL, 0);
1844 }
1845 
1846 #ifdef __ARCH_WANT_SYS_FORK
1847 SYSCALL_DEFINE0(fork)
1848 {
1849 #ifdef CONFIG_MMU
1850         return _do_fork(SIGCHLD, 0, 0, NULL, NULL, 0);
1851 #else
1852         /* can not support in nommu mode */
1853         return -EINVAL;
1854 #endif
1855 }
1856 #endif
1857 
1858 #ifdef __ARCH_WANT_SYS_VFORK
1859 SYSCALL_DEFINE0(vfork)
1860 {
1861         return _do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0,
1862                         0, NULL, NULL, 0);
1863 }
1864 #endif
1865 
1866 #ifdef __ARCH_WANT_SYS_CLONE
1867 #ifdef CONFIG_CLONE_BACKWARDS
1868 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1869                  int __user *, parent_tidptr,
1870                  unsigned long, tls,
1871                  int __user *, child_tidptr)
1872 #elif defined(CONFIG_CLONE_BACKWARDS2)
1873 SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
1874                  int __user *, parent_tidptr,
1875                  int __user *, child_tidptr,
1876                  unsigned long, tls)
1877 #elif defined(CONFIG_CLONE_BACKWARDS3)
1878 SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
1879                 int, stack_size,
1880                 int __user *, parent_tidptr,
1881                 int __user *, child_tidptr,
1882                 unsigned long, tls)
1883 #else
1884 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1885                  int __user *, parent_tidptr,
1886                  int __user *, child_tidptr,
1887                  unsigned long, tls)
1888 #endif
1889 {
1890         return _do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr, tls);
1891 }
1892 #endif
1893 
1894 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1895 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1896 #endif
1897 
1898 static void sighand_ctor(void *data)
1899 {
1900         struct sighand_struct *sighand = data;
1901 
1902         spin_lock_init(&sighand->siglock);
1903         init_waitqueue_head(&sighand->signalfd_wqh);
1904 }
1905 
1906 void __init proc_caches_init(void)
1907 {
1908         sighand_cachep = kmem_cache_create("sighand_cache",
1909                         sizeof(struct sighand_struct), 0,
1910                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1911                         SLAB_NOTRACK|SLAB_ACCOUNT, sighand_ctor);
1912         signal_cachep = kmem_cache_create("signal_cache",
1913                         sizeof(struct signal_struct), 0,
1914                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK|SLAB_ACCOUNT,
1915                         NULL);
1916         files_cachep = kmem_cache_create("files_cache",
1917                         sizeof(struct files_struct), 0,
1918                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK|SLAB_ACCOUNT,
1919                         NULL);
1920         fs_cachep = kmem_cache_create("fs_cache",
1921                         sizeof(struct fs_struct), 0,
1922                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK|SLAB_ACCOUNT,
1923                         NULL);
1924         /*
1925          * FIXME! The "sizeof(struct mm_struct)" currently includes the
1926          * whole struct cpumask for the OFFSTACK case. We could change
1927          * this to *only* allocate as much of it as required by the
1928          * maximum number of CPU's we can ever have.  The cpumask_allocation
1929          * is at the end of the structure, exactly for that reason.
1930          */
1931         mm_cachep = kmem_cache_create("mm_struct",
1932                         sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1933                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK|SLAB_ACCOUNT,
1934                         NULL);
1935         vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_ACCOUNT);
1936         mmap_init();
1937         nsproxy_cache_init();
1938 }
1939 
1940 /*
1941  * Check constraints on flags passed to the unshare system call.
1942  */
1943 static int check_unshare_flags(unsigned long unshare_flags)
1944 {
1945         if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1946                                 CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1947                                 CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
1948                                 CLONE_NEWUSER|CLONE_NEWPID|CLONE_NEWCGROUP))
1949                 return -EINVAL;
1950         /*
1951          * Not implemented, but pretend it works if there is nothing
1952          * to unshare.  Note that unsharing the address space or the
1953          * signal handlers also need to unshare the signal queues (aka
1954          * CLONE_THREAD).
1955          */
1956         if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
1957                 if (!thread_group_empty(current))
1958                         return -EINVAL;
1959         }
1960         if (unshare_flags & (CLONE_SIGHAND | CLONE_VM)) {
1961                 if (atomic_read(&current->sighand->count) > 1)
1962                         return -EINVAL;
1963         }
1964         if (unshare_flags & CLONE_VM) {
1965                 if (!current_is_single_threaded())
1966                         return -EINVAL;
1967         }
1968 
1969         return 0;
1970 }
1971 
1972 /*
1973  * Unshare the filesystem structure if it is being shared
1974  */
1975 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1976 {
1977         struct fs_struct *fs = current->fs;
1978 
1979         if (!(unshare_flags & CLONE_FS) || !fs)
1980                 return 0;
1981 
1982         /* don't need lock here; in the worst case we'll do useless copy */
1983         if (fs->users == 1)
1984                 return 0;
1985 
1986         *new_fsp = copy_fs_struct(fs);
1987         if (!*new_fsp)
1988                 return -ENOMEM;
1989 
1990         return 0;
1991 }
1992 
1993 /*
1994  * Unshare file descriptor table if it is being shared
1995  */
1996 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1997 {
1998         struct files_struct *fd = current->files;
1999         int error = 0;
2000 
2001         if ((unshare_flags & CLONE_FILES) &&
2002             (fd && atomic_read(&fd->count) > 1)) {
2003                 *new_fdp = dup_fd(fd, &error);
2004                 if (!*new_fdp)
2005                         return error;
2006         }
2007 
2008         return 0;
2009 }
2010 
2011 /*
2012  * unshare allows a process to 'unshare' part of the process
2013  * context which was originally shared using clone.  copy_*
2014  * functions used by do_fork() cannot be used here directly
2015  * because they modify an inactive task_struct that is being
2016  * constructed. Here we are modifying the current, active,
2017  * task_struct.
2018  */
2019 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
2020 {
2021         struct fs_struct *fs, *new_fs = NULL;
2022         struct files_struct *fd, *new_fd = NULL;
2023         struct cred *new_cred = NULL;
2024         struct nsproxy *new_nsproxy = NULL;
2025         int do_sysvsem = 0;
2026         int err;
2027 
2028         /*
2029          * If unsharing a user namespace must also unshare the thread group
2030          * and unshare the filesystem root and working directories.
2031          */
2032         if (unshare_flags & CLONE_NEWUSER)
2033                 unshare_flags |= CLONE_THREAD | CLONE_FS;
2034         /*
2035          * If unsharing vm, must also unshare signal handlers.
2036          */
2037         if (unshare_flags & CLONE_VM)
2038                 unshare_flags |= CLONE_SIGHAND;
2039         /*
2040          * If unsharing a signal handlers, must also unshare the signal queues.
2041          */
2042         if (unshare_flags & CLONE_SIGHAND)
2043                 unshare_flags |= CLONE_THREAD;
2044         /*
2045          * If unsharing namespace, must also unshare filesystem information.
2046          */
2047         if (unshare_flags & CLONE_NEWNS)
2048                 unshare_flags |= CLONE_FS;
2049 
2050         err = check_unshare_flags(unshare_flags);
2051         if (err)
2052                 goto bad_unshare_out;
2053         /*
2054          * CLONE_NEWIPC must also detach from the undolist: after switching
2055          * to a new ipc namespace, the semaphore arrays from the old
2056          * namespace are unreachable.
2057          */
2058         if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
2059                 do_sysvsem = 1;
2060         err = unshare_fs(unshare_flags, &new_fs);
2061         if (err)
2062                 goto bad_unshare_out;
2063         err = unshare_fd(unshare_flags, &new_fd);
2064         if (err)
2065                 goto bad_unshare_cleanup_fs;
2066         err = unshare_userns(unshare_flags, &new_cred);
2067         if (err)
2068                 goto bad_unshare_cleanup_fd;
2069         err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
2070                                          new_cred, new_fs);
2071         if (err)
2072                 goto bad_unshare_cleanup_cred;
2073 
2074         if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
2075                 if (do_sysvsem) {
2076                         /*
2077                          * CLONE_SYSVSEM is equivalent to sys_exit().
2078                          */
2079                         exit_sem(current);
2080                 }
2081                 if (unshare_flags & CLONE_NEWIPC) {
2082                         /* Orphan segments in old ns (see sem above). */
2083                         exit_shm(current);
2084                         shm_init_task(current);
2085                 }
2086 
2087                 if (new_nsproxy)
2088                         switch_task_namespaces(current, new_nsproxy);
2089 
2090                 task_lock(current);
2091 
2092                 if (new_fs) {
2093                         fs = current->fs;
2094                         spin_lock(&fs->lock);
2095                         current->fs = new_fs;
2096                         if (--fs->users)
2097                                 new_fs = NULL;
2098                         else
2099                                 new_fs = fs;
2100                         spin_unlock(&fs->lock);
2101                 }
2102 
2103                 if (new_fd) {
2104                         fd = current->files;
2105                         current->files = new_fd;
2106                         new_fd = fd;
2107                 }
2108 
2109                 task_unlock(current);
2110 
2111                 if (new_cred) {
2112                         /* Install the new user namespace */
2113                         commit_creds(new_cred);
2114                         new_cred = NULL;
2115                 }
2116         }
2117 
2118 bad_unshare_cleanup_cred:
2119         if (new_cred)
2120                 put_cred(new_cred);
2121 bad_unshare_cleanup_fd:
2122         if (new_fd)
2123                 put_files_struct(new_fd);
2124 
2125 bad_unshare_cleanup_fs:
2126         if (new_fs)
2127                 free_fs_struct(new_fs);
2128 
2129 bad_unshare_out:
2130         return err;
2131 }
2132 
2133 /*
2134  *      Helper to unshare the files of the current task.
2135  *      We don't want to expose copy_files internals to
2136  *      the exec layer of the kernel.
2137  */
2138 
2139 int unshare_files(struct files_struct **displaced)
2140 {
2141         struct task_struct *task = current;
2142         struct files_struct *copy = NULL;
2143         int error;
2144 
2145         error = unshare_fd(CLONE_FILES, &copy);
2146         if (error || !copy) {
2147                 *displaced = NULL;
2148                 return error;
2149         }
2150         *displaced = task->files;
2151         task_lock(task);
2152         task->files = copy;
2153         task_unlock(task);
2154         return 0;
2155 }
2156 
2157 int sysctl_max_threads(struct ctl_table *table, int write,
2158                        void __user *buffer, size_t *lenp, loff_t *ppos)
2159 {
2160         struct ctl_table t;
2161         int ret;
2162         int threads = max_threads;
2163         int min = MIN_THREADS;
2164         int max = MAX_THREADS;
2165 
2166         t = *table;
2167         t.data = &threads;
2168         t.extra1 = &min;
2169         t.extra2 = &max;
2170 
2171         ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
2172         if (ret || !write)
2173                 return ret;
2174 
2175         set_max_threads(threads);
2176 
2177         return 0;
2178 }
2179 

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