Version:  2.0.40 2.2.26 2.4.37 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19

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

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