xref: /openbmc/linux/kernel/fork.c (revision b34e08d5)
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_pages_node(node, THREADINFO_GFP_ACCOUNTED,
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_memcg_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 static struct task_struct *dup_task_struct(struct task_struct *orig)
298 {
299 	struct task_struct *tsk;
300 	struct thread_info *ti;
301 	unsigned long *stackend;
302 	int node = tsk_fork_get_node(orig);
303 	int err;
304 
305 	tsk = alloc_task_struct_node(node);
306 	if (!tsk)
307 		return NULL;
308 
309 	ti = alloc_thread_info_node(tsk, node);
310 	if (!ti)
311 		goto free_tsk;
312 
313 	err = arch_dup_task_struct(tsk, orig);
314 	if (err)
315 		goto free_ti;
316 
317 	tsk->stack = ti;
318 
319 	setup_thread_stack(tsk, orig);
320 	clear_user_return_notifier(tsk);
321 	clear_tsk_need_resched(tsk);
322 	stackend = end_of_stack(tsk);
323 	*stackend = STACK_END_MAGIC;	/* for overflow detection */
324 
325 #ifdef CONFIG_CC_STACKPROTECTOR
326 	tsk->stack_canary = get_random_int();
327 #endif
328 
329 	/*
330 	 * One for us, one for whoever does the "release_task()" (usually
331 	 * parent)
332 	 */
333 	atomic_set(&tsk->usage, 2);
334 #ifdef CONFIG_BLK_DEV_IO_TRACE
335 	tsk->btrace_seq = 0;
336 #endif
337 	tsk->splice_pipe = NULL;
338 	tsk->task_frag.page = NULL;
339 
340 	account_kernel_stack(ti, 1);
341 
342 	return tsk;
343 
344 free_ti:
345 	free_thread_info(ti);
346 free_tsk:
347 	free_task_struct(tsk);
348 	return NULL;
349 }
350 
351 #ifdef CONFIG_MMU
352 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
353 {
354 	struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
355 	struct rb_node **rb_link, *rb_parent;
356 	int retval;
357 	unsigned long charge;
358 
359 	uprobe_start_dup_mmap();
360 	down_write(&oldmm->mmap_sem);
361 	flush_cache_dup_mm(oldmm);
362 	uprobe_dup_mmap(oldmm, mm);
363 	/*
364 	 * Not linked in yet - no deadlock potential:
365 	 */
366 	down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
367 
368 	mm->locked_vm = 0;
369 	mm->mmap = NULL;
370 	mm->vmacache_seqnum = 0;
371 	mm->map_count = 0;
372 	cpumask_clear(mm_cpumask(mm));
373 	mm->mm_rb = RB_ROOT;
374 	rb_link = &mm->mm_rb.rb_node;
375 	rb_parent = NULL;
376 	pprev = &mm->mmap;
377 	retval = ksm_fork(mm, oldmm);
378 	if (retval)
379 		goto out;
380 	retval = khugepaged_fork(mm, oldmm);
381 	if (retval)
382 		goto out;
383 
384 	prev = NULL;
385 	for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
386 		struct file *file;
387 
388 		if (mpnt->vm_flags & VM_DONTCOPY) {
389 			vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
390 							-vma_pages(mpnt));
391 			continue;
392 		}
393 		charge = 0;
394 		if (mpnt->vm_flags & VM_ACCOUNT) {
395 			unsigned long len = vma_pages(mpnt);
396 
397 			if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
398 				goto fail_nomem;
399 			charge = len;
400 		}
401 		tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
402 		if (!tmp)
403 			goto fail_nomem;
404 		*tmp = *mpnt;
405 		INIT_LIST_HEAD(&tmp->anon_vma_chain);
406 		retval = vma_dup_policy(mpnt, tmp);
407 		if (retval)
408 			goto fail_nomem_policy;
409 		tmp->vm_mm = mm;
410 		if (anon_vma_fork(tmp, mpnt))
411 			goto fail_nomem_anon_vma_fork;
412 		tmp->vm_flags &= ~VM_LOCKED;
413 		tmp->vm_next = tmp->vm_prev = NULL;
414 		file = tmp->vm_file;
415 		if (file) {
416 			struct inode *inode = file_inode(file);
417 			struct address_space *mapping = file->f_mapping;
418 
419 			get_file(file);
420 			if (tmp->vm_flags & VM_DENYWRITE)
421 				atomic_dec(&inode->i_writecount);
422 			mutex_lock(&mapping->i_mmap_mutex);
423 			if (tmp->vm_flags & VM_SHARED)
424 				mapping->i_mmap_writable++;
425 			flush_dcache_mmap_lock(mapping);
426 			/* insert tmp into the share list, just after mpnt */
427 			if (unlikely(tmp->vm_flags & VM_NONLINEAR))
428 				vma_nonlinear_insert(tmp,
429 						&mapping->i_mmap_nonlinear);
430 			else
431 				vma_interval_tree_insert_after(tmp, mpnt,
432 							&mapping->i_mmap);
433 			flush_dcache_mmap_unlock(mapping);
434 			mutex_unlock(&mapping->i_mmap_mutex);
435 		}
436 
437 		/*
438 		 * Clear hugetlb-related page reserves for children. This only
439 		 * affects MAP_PRIVATE mappings. Faults generated by the child
440 		 * are not guaranteed to succeed, even if read-only
441 		 */
442 		if (is_vm_hugetlb_page(tmp))
443 			reset_vma_resv_huge_pages(tmp);
444 
445 		/*
446 		 * Link in the new vma and copy the page table entries.
447 		 */
448 		*pprev = tmp;
449 		pprev = &tmp->vm_next;
450 		tmp->vm_prev = prev;
451 		prev = tmp;
452 
453 		__vma_link_rb(mm, tmp, rb_link, rb_parent);
454 		rb_link = &tmp->vm_rb.rb_right;
455 		rb_parent = &tmp->vm_rb;
456 
457 		mm->map_count++;
458 		retval = copy_page_range(mm, oldmm, mpnt);
459 
460 		if (tmp->vm_ops && tmp->vm_ops->open)
461 			tmp->vm_ops->open(tmp);
462 
463 		if (retval)
464 			goto out;
465 	}
466 	/* a new mm has just been created */
467 	arch_dup_mmap(oldmm, mm);
468 	retval = 0;
469 out:
470 	up_write(&mm->mmap_sem);
471 	flush_tlb_mm(oldmm);
472 	up_write(&oldmm->mmap_sem);
473 	uprobe_end_dup_mmap();
474 	return retval;
475 fail_nomem_anon_vma_fork:
476 	mpol_put(vma_policy(tmp));
477 fail_nomem_policy:
478 	kmem_cache_free(vm_area_cachep, tmp);
479 fail_nomem:
480 	retval = -ENOMEM;
481 	vm_unacct_memory(charge);
482 	goto out;
483 }
484 
485 static inline int mm_alloc_pgd(struct mm_struct *mm)
486 {
487 	mm->pgd = pgd_alloc(mm);
488 	if (unlikely(!mm->pgd))
489 		return -ENOMEM;
490 	return 0;
491 }
492 
493 static inline void mm_free_pgd(struct mm_struct *mm)
494 {
495 	pgd_free(mm, mm->pgd);
496 }
497 #else
498 #define dup_mmap(mm, oldmm)	(0)
499 #define mm_alloc_pgd(mm)	(0)
500 #define mm_free_pgd(mm)
501 #endif /* CONFIG_MMU */
502 
503 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
504 
505 #define allocate_mm()	(kmem_cache_alloc(mm_cachep, GFP_KERNEL))
506 #define free_mm(mm)	(kmem_cache_free(mm_cachep, (mm)))
507 
508 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
509 
510 static int __init coredump_filter_setup(char *s)
511 {
512 	default_dump_filter =
513 		(simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
514 		MMF_DUMP_FILTER_MASK;
515 	return 1;
516 }
517 
518 __setup("coredump_filter=", coredump_filter_setup);
519 
520 #include <linux/init_task.h>
521 
522 static void mm_init_aio(struct mm_struct *mm)
523 {
524 #ifdef CONFIG_AIO
525 	spin_lock_init(&mm->ioctx_lock);
526 	mm->ioctx_table = NULL;
527 #endif
528 }
529 
530 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
531 {
532 	atomic_set(&mm->mm_users, 1);
533 	atomic_set(&mm->mm_count, 1);
534 	init_rwsem(&mm->mmap_sem);
535 	INIT_LIST_HEAD(&mm->mmlist);
536 	mm->core_state = NULL;
537 	atomic_long_set(&mm->nr_ptes, 0);
538 	memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
539 	spin_lock_init(&mm->page_table_lock);
540 	mm_init_aio(mm);
541 	mm_init_owner(mm, p);
542 	clear_tlb_flush_pending(mm);
543 
544 	if (current->mm) {
545 		mm->flags = current->mm->flags & MMF_INIT_MASK;
546 		mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
547 	} else {
548 		mm->flags = default_dump_filter;
549 		mm->def_flags = 0;
550 	}
551 
552 	if (likely(!mm_alloc_pgd(mm))) {
553 		mmu_notifier_mm_init(mm);
554 		return mm;
555 	}
556 
557 	free_mm(mm);
558 	return NULL;
559 }
560 
561 static void check_mm(struct mm_struct *mm)
562 {
563 	int i;
564 
565 	for (i = 0; i < NR_MM_COUNTERS; i++) {
566 		long x = atomic_long_read(&mm->rss_stat.count[i]);
567 
568 		if (unlikely(x))
569 			printk(KERN_ALERT "BUG: Bad rss-counter state "
570 					  "mm:%p idx:%d val:%ld\n", mm, i, x);
571 	}
572 
573 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
574 	VM_BUG_ON(mm->pmd_huge_pte);
575 #endif
576 }
577 
578 /*
579  * Allocate and initialize an mm_struct.
580  */
581 struct mm_struct *mm_alloc(void)
582 {
583 	struct mm_struct *mm;
584 
585 	mm = allocate_mm();
586 	if (!mm)
587 		return NULL;
588 
589 	memset(mm, 0, sizeof(*mm));
590 	mm_init_cpumask(mm);
591 	return mm_init(mm, current);
592 }
593 
594 /*
595  * Called when the last reference to the mm
596  * is dropped: either by a lazy thread or by
597  * mmput. Free the page directory and the mm.
598  */
599 void __mmdrop(struct mm_struct *mm)
600 {
601 	BUG_ON(mm == &init_mm);
602 	mm_free_pgd(mm);
603 	destroy_context(mm);
604 	mmu_notifier_mm_destroy(mm);
605 	check_mm(mm);
606 	free_mm(mm);
607 }
608 EXPORT_SYMBOL_GPL(__mmdrop);
609 
610 /*
611  * Decrement the use count and release all resources for an mm.
612  */
613 void mmput(struct mm_struct *mm)
614 {
615 	might_sleep();
616 
617 	if (atomic_dec_and_test(&mm->mm_users)) {
618 		uprobe_clear_state(mm);
619 		exit_aio(mm);
620 		ksm_exit(mm);
621 		khugepaged_exit(mm); /* must run before exit_mmap */
622 		exit_mmap(mm);
623 		set_mm_exe_file(mm, NULL);
624 		if (!list_empty(&mm->mmlist)) {
625 			spin_lock(&mmlist_lock);
626 			list_del(&mm->mmlist);
627 			spin_unlock(&mmlist_lock);
628 		}
629 		if (mm->binfmt)
630 			module_put(mm->binfmt->module);
631 		mmdrop(mm);
632 	}
633 }
634 EXPORT_SYMBOL_GPL(mmput);
635 
636 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
637 {
638 	if (new_exe_file)
639 		get_file(new_exe_file);
640 	if (mm->exe_file)
641 		fput(mm->exe_file);
642 	mm->exe_file = new_exe_file;
643 }
644 
645 struct file *get_mm_exe_file(struct mm_struct *mm)
646 {
647 	struct file *exe_file;
648 
649 	/* We need mmap_sem to protect against races with removal of exe_file */
650 	down_read(&mm->mmap_sem);
651 	exe_file = mm->exe_file;
652 	if (exe_file)
653 		get_file(exe_file);
654 	up_read(&mm->mmap_sem);
655 	return exe_file;
656 }
657 
658 static void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
659 {
660 	/* It's safe to write the exe_file pointer without exe_file_lock because
661 	 * this is called during fork when the task is not yet in /proc */
662 	newmm->exe_file = get_mm_exe_file(oldmm);
663 }
664 
665 /**
666  * get_task_mm - acquire a reference to the task's mm
667  *
668  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
669  * this kernel workthread has transiently adopted a user mm with use_mm,
670  * to do its AIO) is not set and if so returns a reference to it, after
671  * bumping up the use count.  User must release the mm via mmput()
672  * after use.  Typically used by /proc and ptrace.
673  */
674 struct mm_struct *get_task_mm(struct task_struct *task)
675 {
676 	struct mm_struct *mm;
677 
678 	task_lock(task);
679 	mm = task->mm;
680 	if (mm) {
681 		if (task->flags & PF_KTHREAD)
682 			mm = NULL;
683 		else
684 			atomic_inc(&mm->mm_users);
685 	}
686 	task_unlock(task);
687 	return mm;
688 }
689 EXPORT_SYMBOL_GPL(get_task_mm);
690 
691 struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
692 {
693 	struct mm_struct *mm;
694 	int err;
695 
696 	err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
697 	if (err)
698 		return ERR_PTR(err);
699 
700 	mm = get_task_mm(task);
701 	if (mm && mm != current->mm &&
702 			!ptrace_may_access(task, mode)) {
703 		mmput(mm);
704 		mm = ERR_PTR(-EACCES);
705 	}
706 	mutex_unlock(&task->signal->cred_guard_mutex);
707 
708 	return mm;
709 }
710 
711 static void complete_vfork_done(struct task_struct *tsk)
712 {
713 	struct completion *vfork;
714 
715 	task_lock(tsk);
716 	vfork = tsk->vfork_done;
717 	if (likely(vfork)) {
718 		tsk->vfork_done = NULL;
719 		complete(vfork);
720 	}
721 	task_unlock(tsk);
722 }
723 
724 static int wait_for_vfork_done(struct task_struct *child,
725 				struct completion *vfork)
726 {
727 	int killed;
728 
729 	freezer_do_not_count();
730 	killed = wait_for_completion_killable(vfork);
731 	freezer_count();
732 
733 	if (killed) {
734 		task_lock(child);
735 		child->vfork_done = NULL;
736 		task_unlock(child);
737 	}
738 
739 	put_task_struct(child);
740 	return killed;
741 }
742 
743 /* Please note the differences between mmput and mm_release.
744  * mmput is called whenever we stop holding onto a mm_struct,
745  * error success whatever.
746  *
747  * mm_release is called after a mm_struct has been removed
748  * from the current process.
749  *
750  * This difference is important for error handling, when we
751  * only half set up a mm_struct for a new process and need to restore
752  * the old one.  Because we mmput the new mm_struct before
753  * restoring the old one. . .
754  * Eric Biederman 10 January 1998
755  */
756 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
757 {
758 	/* Get rid of any futexes when releasing the mm */
759 #ifdef CONFIG_FUTEX
760 	if (unlikely(tsk->robust_list)) {
761 		exit_robust_list(tsk);
762 		tsk->robust_list = NULL;
763 	}
764 #ifdef CONFIG_COMPAT
765 	if (unlikely(tsk->compat_robust_list)) {
766 		compat_exit_robust_list(tsk);
767 		tsk->compat_robust_list = NULL;
768 	}
769 #endif
770 	if (unlikely(!list_empty(&tsk->pi_state_list)))
771 		exit_pi_state_list(tsk);
772 #endif
773 
774 	uprobe_free_utask(tsk);
775 
776 	/* Get rid of any cached register state */
777 	deactivate_mm(tsk, mm);
778 
779 	/*
780 	 * If we're exiting normally, clear a user-space tid field if
781 	 * requested.  We leave this alone when dying by signal, to leave
782 	 * the value intact in a core dump, and to save the unnecessary
783 	 * trouble, say, a killed vfork parent shouldn't touch this mm.
784 	 * Userland only wants this done for a sys_exit.
785 	 */
786 	if (tsk->clear_child_tid) {
787 		if (!(tsk->flags & PF_SIGNALED) &&
788 		    atomic_read(&mm->mm_users) > 1) {
789 			/*
790 			 * We don't check the error code - if userspace has
791 			 * not set up a proper pointer then tough luck.
792 			 */
793 			put_user(0, tsk->clear_child_tid);
794 			sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
795 					1, NULL, NULL, 0);
796 		}
797 		tsk->clear_child_tid = NULL;
798 	}
799 
800 	/*
801 	 * All done, finally we can wake up parent and return this mm to him.
802 	 * Also kthread_stop() uses this completion for synchronization.
803 	 */
804 	if (tsk->vfork_done)
805 		complete_vfork_done(tsk);
806 }
807 
808 /*
809  * Allocate a new mm structure and copy contents from the
810  * mm structure of the passed in task structure.
811  */
812 static struct mm_struct *dup_mm(struct task_struct *tsk)
813 {
814 	struct mm_struct *mm, *oldmm = current->mm;
815 	int err;
816 
817 	mm = allocate_mm();
818 	if (!mm)
819 		goto fail_nomem;
820 
821 	memcpy(mm, oldmm, sizeof(*mm));
822 	mm_init_cpumask(mm);
823 
824 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
825 	mm->pmd_huge_pte = NULL;
826 #endif
827 	if (!mm_init(mm, tsk))
828 		goto fail_nomem;
829 
830 	if (init_new_context(tsk, mm))
831 		goto fail_nocontext;
832 
833 	dup_mm_exe_file(oldmm, mm);
834 
835 	err = dup_mmap(mm, oldmm);
836 	if (err)
837 		goto free_pt;
838 
839 	mm->hiwater_rss = get_mm_rss(mm);
840 	mm->hiwater_vm = mm->total_vm;
841 
842 	if (mm->binfmt && !try_module_get(mm->binfmt->module))
843 		goto free_pt;
844 
845 	return mm;
846 
847 free_pt:
848 	/* don't put binfmt in mmput, we haven't got module yet */
849 	mm->binfmt = NULL;
850 	mmput(mm);
851 
852 fail_nomem:
853 	return NULL;
854 
855 fail_nocontext:
856 	/*
857 	 * If init_new_context() failed, we cannot use mmput() to free the mm
858 	 * because it calls destroy_context()
859 	 */
860 	mm_free_pgd(mm);
861 	free_mm(mm);
862 	return NULL;
863 }
864 
865 static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
866 {
867 	struct mm_struct *mm, *oldmm;
868 	int retval;
869 
870 	tsk->min_flt = tsk->maj_flt = 0;
871 	tsk->nvcsw = tsk->nivcsw = 0;
872 #ifdef CONFIG_DETECT_HUNG_TASK
873 	tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
874 #endif
875 
876 	tsk->mm = NULL;
877 	tsk->active_mm = NULL;
878 
879 	/*
880 	 * Are we cloning a kernel thread?
881 	 *
882 	 * We need to steal a active VM for that..
883 	 */
884 	oldmm = current->mm;
885 	if (!oldmm)
886 		return 0;
887 
888 	/* initialize the new vmacache entries */
889 	vmacache_flush(tsk);
890 
891 	if (clone_flags & CLONE_VM) {
892 		atomic_inc(&oldmm->mm_users);
893 		mm = oldmm;
894 		goto good_mm;
895 	}
896 
897 	retval = -ENOMEM;
898 	mm = dup_mm(tsk);
899 	if (!mm)
900 		goto fail_nomem;
901 
902 good_mm:
903 	tsk->mm = mm;
904 	tsk->active_mm = mm;
905 	return 0;
906 
907 fail_nomem:
908 	return retval;
909 }
910 
911 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
912 {
913 	struct fs_struct *fs = current->fs;
914 	if (clone_flags & CLONE_FS) {
915 		/* tsk->fs is already what we want */
916 		spin_lock(&fs->lock);
917 		if (fs->in_exec) {
918 			spin_unlock(&fs->lock);
919 			return -EAGAIN;
920 		}
921 		fs->users++;
922 		spin_unlock(&fs->lock);
923 		return 0;
924 	}
925 	tsk->fs = copy_fs_struct(fs);
926 	if (!tsk->fs)
927 		return -ENOMEM;
928 	return 0;
929 }
930 
931 static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
932 {
933 	struct files_struct *oldf, *newf;
934 	int error = 0;
935 
936 	/*
937 	 * A background process may not have any files ...
938 	 */
939 	oldf = current->files;
940 	if (!oldf)
941 		goto out;
942 
943 	if (clone_flags & CLONE_FILES) {
944 		atomic_inc(&oldf->count);
945 		goto out;
946 	}
947 
948 	newf = dup_fd(oldf, &error);
949 	if (!newf)
950 		goto out;
951 
952 	tsk->files = newf;
953 	error = 0;
954 out:
955 	return error;
956 }
957 
958 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
959 {
960 #ifdef CONFIG_BLOCK
961 	struct io_context *ioc = current->io_context;
962 	struct io_context *new_ioc;
963 
964 	if (!ioc)
965 		return 0;
966 	/*
967 	 * Share io context with parent, if CLONE_IO is set
968 	 */
969 	if (clone_flags & CLONE_IO) {
970 		ioc_task_link(ioc);
971 		tsk->io_context = ioc;
972 	} else if (ioprio_valid(ioc->ioprio)) {
973 		new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
974 		if (unlikely(!new_ioc))
975 			return -ENOMEM;
976 
977 		new_ioc->ioprio = ioc->ioprio;
978 		put_io_context(new_ioc);
979 	}
980 #endif
981 	return 0;
982 }
983 
984 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
985 {
986 	struct sighand_struct *sig;
987 
988 	if (clone_flags & CLONE_SIGHAND) {
989 		atomic_inc(&current->sighand->count);
990 		return 0;
991 	}
992 	sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
993 	rcu_assign_pointer(tsk->sighand, sig);
994 	if (!sig)
995 		return -ENOMEM;
996 	atomic_set(&sig->count, 1);
997 	memcpy(sig->action, current->sighand->action, sizeof(sig->action));
998 	return 0;
999 }
1000 
1001 void __cleanup_sighand(struct sighand_struct *sighand)
1002 {
1003 	if (atomic_dec_and_test(&sighand->count)) {
1004 		signalfd_cleanup(sighand);
1005 		kmem_cache_free(sighand_cachep, sighand);
1006 	}
1007 }
1008 
1009 
1010 /*
1011  * Initialize POSIX timer handling for a thread group.
1012  */
1013 static void posix_cpu_timers_init_group(struct signal_struct *sig)
1014 {
1015 	unsigned long cpu_limit;
1016 
1017 	/* Thread group counters. */
1018 	thread_group_cputime_init(sig);
1019 
1020 	cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1021 	if (cpu_limit != RLIM_INFINITY) {
1022 		sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
1023 		sig->cputimer.running = 1;
1024 	}
1025 
1026 	/* The timer lists. */
1027 	INIT_LIST_HEAD(&sig->cpu_timers[0]);
1028 	INIT_LIST_HEAD(&sig->cpu_timers[1]);
1029 	INIT_LIST_HEAD(&sig->cpu_timers[2]);
1030 }
1031 
1032 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1033 {
1034 	struct signal_struct *sig;
1035 
1036 	if (clone_flags & CLONE_THREAD)
1037 		return 0;
1038 
1039 	sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1040 	tsk->signal = sig;
1041 	if (!sig)
1042 		return -ENOMEM;
1043 
1044 	sig->nr_threads = 1;
1045 	atomic_set(&sig->live, 1);
1046 	atomic_set(&sig->sigcnt, 1);
1047 
1048 	/* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */
1049 	sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node);
1050 	tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);
1051 
1052 	init_waitqueue_head(&sig->wait_chldexit);
1053 	sig->curr_target = tsk;
1054 	init_sigpending(&sig->shared_pending);
1055 	INIT_LIST_HEAD(&sig->posix_timers);
1056 
1057 	hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1058 	sig->real_timer.function = it_real_fn;
1059 
1060 	task_lock(current->group_leader);
1061 	memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1062 	task_unlock(current->group_leader);
1063 
1064 	posix_cpu_timers_init_group(sig);
1065 
1066 	tty_audit_fork(sig);
1067 	sched_autogroup_fork(sig);
1068 
1069 #ifdef CONFIG_CGROUPS
1070 	init_rwsem(&sig->group_rwsem);
1071 #endif
1072 
1073 	sig->oom_score_adj = current->signal->oom_score_adj;
1074 	sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1075 
1076 	sig->has_child_subreaper = current->signal->has_child_subreaper ||
1077 				   current->signal->is_child_subreaper;
1078 
1079 	mutex_init(&sig->cred_guard_mutex);
1080 
1081 	return 0;
1082 }
1083 
1084 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1085 {
1086 	current->clear_child_tid = tidptr;
1087 
1088 	return task_pid_vnr(current);
1089 }
1090 
1091 static void rt_mutex_init_task(struct task_struct *p)
1092 {
1093 	raw_spin_lock_init(&p->pi_lock);
1094 #ifdef CONFIG_RT_MUTEXES
1095 	p->pi_waiters = RB_ROOT;
1096 	p->pi_waiters_leftmost = NULL;
1097 	p->pi_blocked_on = NULL;
1098 	p->pi_top_task = NULL;
1099 #endif
1100 }
1101 
1102 #ifdef CONFIG_MM_OWNER
1103 void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
1104 {
1105 	mm->owner = p;
1106 }
1107 #endif /* CONFIG_MM_OWNER */
1108 
1109 /*
1110  * Initialize POSIX timer handling for a single task.
1111  */
1112 static void posix_cpu_timers_init(struct task_struct *tsk)
1113 {
1114 	tsk->cputime_expires.prof_exp = 0;
1115 	tsk->cputime_expires.virt_exp = 0;
1116 	tsk->cputime_expires.sched_exp = 0;
1117 	INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1118 	INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1119 	INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1120 }
1121 
1122 static inline void
1123 init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
1124 {
1125 	 task->pids[type].pid = pid;
1126 }
1127 
1128 /*
1129  * This creates a new process as a copy of the old one,
1130  * but does not actually start it yet.
1131  *
1132  * It copies the registers, and all the appropriate
1133  * parts of the process environment (as per the clone
1134  * flags). The actual kick-off is left to the caller.
1135  */
1136 static struct task_struct *copy_process(unsigned long clone_flags,
1137 					unsigned long stack_start,
1138 					unsigned long stack_size,
1139 					int __user *child_tidptr,
1140 					struct pid *pid,
1141 					int trace)
1142 {
1143 	int retval;
1144 	struct task_struct *p;
1145 
1146 	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1147 		return ERR_PTR(-EINVAL);
1148 
1149 	if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
1150 		return ERR_PTR(-EINVAL);
1151 
1152 	/*
1153 	 * Thread groups must share signals as well, and detached threads
1154 	 * can only be started up within the thread group.
1155 	 */
1156 	if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1157 		return ERR_PTR(-EINVAL);
1158 
1159 	/*
1160 	 * Shared signal handlers imply shared VM. By way of the above,
1161 	 * thread groups also imply shared VM. Blocking this case allows
1162 	 * for various simplifications in other code.
1163 	 */
1164 	if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1165 		return ERR_PTR(-EINVAL);
1166 
1167 	/*
1168 	 * Siblings of global init remain as zombies on exit since they are
1169 	 * not reaped by their parent (swapper). To solve this and to avoid
1170 	 * multi-rooted process trees, prevent global and container-inits
1171 	 * from creating siblings.
1172 	 */
1173 	if ((clone_flags & CLONE_PARENT) &&
1174 				current->signal->flags & SIGNAL_UNKILLABLE)
1175 		return ERR_PTR(-EINVAL);
1176 
1177 	/*
1178 	 * If the new process will be in a different pid or user namespace
1179 	 * do not allow it to share a thread group or signal handlers or
1180 	 * parent with the forking task.
1181 	 */
1182 	if (clone_flags & CLONE_SIGHAND) {
1183 		if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
1184 		    (task_active_pid_ns(current) !=
1185 				current->nsproxy->pid_ns_for_children))
1186 			return ERR_PTR(-EINVAL);
1187 	}
1188 
1189 	retval = security_task_create(clone_flags);
1190 	if (retval)
1191 		goto fork_out;
1192 
1193 	retval = -ENOMEM;
1194 	p = dup_task_struct(current);
1195 	if (!p)
1196 		goto fork_out;
1197 
1198 	ftrace_graph_init_task(p);
1199 	get_seccomp_filter(p);
1200 
1201 	rt_mutex_init_task(p);
1202 
1203 #ifdef CONFIG_PROVE_LOCKING
1204 	DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1205 	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1206 #endif
1207 	retval = -EAGAIN;
1208 	if (atomic_read(&p->real_cred->user->processes) >=
1209 			task_rlimit(p, RLIMIT_NPROC)) {
1210 		if (p->real_cred->user != INIT_USER &&
1211 		    !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
1212 			goto bad_fork_free;
1213 	}
1214 	current->flags &= ~PF_NPROC_EXCEEDED;
1215 
1216 	retval = copy_creds(p, clone_flags);
1217 	if (retval < 0)
1218 		goto bad_fork_free;
1219 
1220 	/*
1221 	 * If multiple threads are within copy_process(), then this check
1222 	 * triggers too late. This doesn't hurt, the check is only there
1223 	 * to stop root fork bombs.
1224 	 */
1225 	retval = -EAGAIN;
1226 	if (nr_threads >= max_threads)
1227 		goto bad_fork_cleanup_count;
1228 
1229 	if (!try_module_get(task_thread_info(p)->exec_domain->module))
1230 		goto bad_fork_cleanup_count;
1231 
1232 	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */
1233 	p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
1234 	p->flags |= PF_FORKNOEXEC;
1235 	INIT_LIST_HEAD(&p->children);
1236 	INIT_LIST_HEAD(&p->sibling);
1237 	rcu_copy_process(p);
1238 	p->vfork_done = NULL;
1239 	spin_lock_init(&p->alloc_lock);
1240 
1241 	init_sigpending(&p->pending);
1242 
1243 	p->utime = p->stime = p->gtime = 0;
1244 	p->utimescaled = p->stimescaled = 0;
1245 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
1246 	p->prev_cputime.utime = p->prev_cputime.stime = 0;
1247 #endif
1248 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
1249 	seqlock_init(&p->vtime_seqlock);
1250 	p->vtime_snap = 0;
1251 	p->vtime_snap_whence = VTIME_SLEEPING;
1252 #endif
1253 
1254 #if defined(SPLIT_RSS_COUNTING)
1255 	memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1256 #endif
1257 
1258 	p->default_timer_slack_ns = current->timer_slack_ns;
1259 
1260 	task_io_accounting_init(&p->ioac);
1261 	acct_clear_integrals(p);
1262 
1263 	posix_cpu_timers_init(p);
1264 
1265 	do_posix_clock_monotonic_gettime(&p->start_time);
1266 	p->real_start_time = p->start_time;
1267 	monotonic_to_bootbased(&p->real_start_time);
1268 	p->io_context = NULL;
1269 	p->audit_context = NULL;
1270 	if (clone_flags & CLONE_THREAD)
1271 		threadgroup_change_begin(current);
1272 	cgroup_fork(p);
1273 #ifdef CONFIG_NUMA
1274 	p->mempolicy = mpol_dup(p->mempolicy);
1275 	if (IS_ERR(p->mempolicy)) {
1276 		retval = PTR_ERR(p->mempolicy);
1277 		p->mempolicy = NULL;
1278 		goto bad_fork_cleanup_threadgroup_lock;
1279 	}
1280 #endif
1281 #ifdef CONFIG_CPUSETS
1282 	p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
1283 	p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
1284 	seqcount_init(&p->mems_allowed_seq);
1285 #endif
1286 #ifdef CONFIG_TRACE_IRQFLAGS
1287 	p->irq_events = 0;
1288 	p->hardirqs_enabled = 0;
1289 	p->hardirq_enable_ip = 0;
1290 	p->hardirq_enable_event = 0;
1291 	p->hardirq_disable_ip = _THIS_IP_;
1292 	p->hardirq_disable_event = 0;
1293 	p->softirqs_enabled = 1;
1294 	p->softirq_enable_ip = _THIS_IP_;
1295 	p->softirq_enable_event = 0;
1296 	p->softirq_disable_ip = 0;
1297 	p->softirq_disable_event = 0;
1298 	p->hardirq_context = 0;
1299 	p->softirq_context = 0;
1300 #endif
1301 #ifdef CONFIG_LOCKDEP
1302 	p->lockdep_depth = 0; /* no locks held yet */
1303 	p->curr_chain_key = 0;
1304 	p->lockdep_recursion = 0;
1305 #endif
1306 
1307 #ifdef CONFIG_DEBUG_MUTEXES
1308 	p->blocked_on = NULL; /* not blocked yet */
1309 #endif
1310 #ifdef CONFIG_MEMCG
1311 	p->memcg_batch.do_batch = 0;
1312 	p->memcg_batch.memcg = NULL;
1313 #endif
1314 #ifdef CONFIG_BCACHE
1315 	p->sequential_io	= 0;
1316 	p->sequential_io_avg	= 0;
1317 #endif
1318 
1319 	/* Perform scheduler related setup. Assign this task to a CPU. */
1320 	retval = sched_fork(clone_flags, p);
1321 	if (retval)
1322 		goto bad_fork_cleanup_policy;
1323 
1324 	retval = perf_event_init_task(p);
1325 	if (retval)
1326 		goto bad_fork_cleanup_policy;
1327 	retval = audit_alloc(p);
1328 	if (retval)
1329 		goto bad_fork_cleanup_policy;
1330 	/* copy all the process information */
1331 	retval = copy_semundo(clone_flags, p);
1332 	if (retval)
1333 		goto bad_fork_cleanup_audit;
1334 	retval = copy_files(clone_flags, p);
1335 	if (retval)
1336 		goto bad_fork_cleanup_semundo;
1337 	retval = copy_fs(clone_flags, p);
1338 	if (retval)
1339 		goto bad_fork_cleanup_files;
1340 	retval = copy_sighand(clone_flags, p);
1341 	if (retval)
1342 		goto bad_fork_cleanup_fs;
1343 	retval = copy_signal(clone_flags, p);
1344 	if (retval)
1345 		goto bad_fork_cleanup_sighand;
1346 	retval = copy_mm(clone_flags, p);
1347 	if (retval)
1348 		goto bad_fork_cleanup_signal;
1349 	retval = copy_namespaces(clone_flags, p);
1350 	if (retval)
1351 		goto bad_fork_cleanup_mm;
1352 	retval = copy_io(clone_flags, p);
1353 	if (retval)
1354 		goto bad_fork_cleanup_namespaces;
1355 	retval = copy_thread(clone_flags, stack_start, stack_size, p);
1356 	if (retval)
1357 		goto bad_fork_cleanup_io;
1358 
1359 	if (pid != &init_struct_pid) {
1360 		retval = -ENOMEM;
1361 		pid = alloc_pid(p->nsproxy->pid_ns_for_children);
1362 		if (!pid)
1363 			goto bad_fork_cleanup_io;
1364 	}
1365 
1366 	p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1367 	/*
1368 	 * Clear TID on mm_release()?
1369 	 */
1370 	p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
1371 #ifdef CONFIG_BLOCK
1372 	p->plug = NULL;
1373 #endif
1374 #ifdef CONFIG_FUTEX
1375 	p->robust_list = NULL;
1376 #ifdef CONFIG_COMPAT
1377 	p->compat_robust_list = NULL;
1378 #endif
1379 	INIT_LIST_HEAD(&p->pi_state_list);
1380 	p->pi_state_cache = NULL;
1381 #endif
1382 	/*
1383 	 * sigaltstack should be cleared when sharing the same VM
1384 	 */
1385 	if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1386 		p->sas_ss_sp = p->sas_ss_size = 0;
1387 
1388 	/*
1389 	 * Syscall tracing and stepping should be turned off in the
1390 	 * child regardless of CLONE_PTRACE.
1391 	 */
1392 	user_disable_single_step(p);
1393 	clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1394 #ifdef TIF_SYSCALL_EMU
1395 	clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1396 #endif
1397 	clear_all_latency_tracing(p);
1398 
1399 	/* ok, now we should be set up.. */
1400 	p->pid = pid_nr(pid);
1401 	if (clone_flags & CLONE_THREAD) {
1402 		p->exit_signal = -1;
1403 		p->group_leader = current->group_leader;
1404 		p->tgid = current->tgid;
1405 	} else {
1406 		if (clone_flags & CLONE_PARENT)
1407 			p->exit_signal = current->group_leader->exit_signal;
1408 		else
1409 			p->exit_signal = (clone_flags & CSIGNAL);
1410 		p->group_leader = p;
1411 		p->tgid = p->pid;
1412 	}
1413 
1414 	p->nr_dirtied = 0;
1415 	p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
1416 	p->dirty_paused_when = 0;
1417 
1418 	p->pdeath_signal = 0;
1419 	INIT_LIST_HEAD(&p->thread_group);
1420 	p->task_works = NULL;
1421 
1422 	/*
1423 	 * Make it visible to the rest of the system, but dont wake it up yet.
1424 	 * Need tasklist lock for parent etc handling!
1425 	 */
1426 	write_lock_irq(&tasklist_lock);
1427 
1428 	/* CLONE_PARENT re-uses the old parent */
1429 	if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1430 		p->real_parent = current->real_parent;
1431 		p->parent_exec_id = current->parent_exec_id;
1432 	} else {
1433 		p->real_parent = current;
1434 		p->parent_exec_id = current->self_exec_id;
1435 	}
1436 
1437 	spin_lock(&current->sighand->siglock);
1438 
1439 	/*
1440 	 * Process group and session signals need to be delivered to just the
1441 	 * parent before the fork or both the parent and the child after the
1442 	 * fork. Restart if a signal comes in before we add the new process to
1443 	 * it's process group.
1444 	 * A fatal signal pending means that current will exit, so the new
1445 	 * thread can't slip out of an OOM kill (or normal SIGKILL).
1446 	*/
1447 	recalc_sigpending();
1448 	if (signal_pending(current)) {
1449 		spin_unlock(&current->sighand->siglock);
1450 		write_unlock_irq(&tasklist_lock);
1451 		retval = -ERESTARTNOINTR;
1452 		goto bad_fork_free_pid;
1453 	}
1454 
1455 	if (likely(p->pid)) {
1456 		ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
1457 
1458 		init_task_pid(p, PIDTYPE_PID, pid);
1459 		if (thread_group_leader(p)) {
1460 			init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
1461 			init_task_pid(p, PIDTYPE_SID, task_session(current));
1462 
1463 			if (is_child_reaper(pid)) {
1464 				ns_of_pid(pid)->child_reaper = p;
1465 				p->signal->flags |= SIGNAL_UNKILLABLE;
1466 			}
1467 
1468 			p->signal->leader_pid = pid;
1469 			p->signal->tty = tty_kref_get(current->signal->tty);
1470 			list_add_tail(&p->sibling, &p->real_parent->children);
1471 			list_add_tail_rcu(&p->tasks, &init_task.tasks);
1472 			attach_pid(p, PIDTYPE_PGID);
1473 			attach_pid(p, PIDTYPE_SID);
1474 			__this_cpu_inc(process_counts);
1475 		} else {
1476 			current->signal->nr_threads++;
1477 			atomic_inc(&current->signal->live);
1478 			atomic_inc(&current->signal->sigcnt);
1479 			list_add_tail_rcu(&p->thread_group,
1480 					  &p->group_leader->thread_group);
1481 			list_add_tail_rcu(&p->thread_node,
1482 					  &p->signal->thread_head);
1483 		}
1484 		attach_pid(p, PIDTYPE_PID);
1485 		nr_threads++;
1486 	}
1487 
1488 	total_forks++;
1489 	spin_unlock(&current->sighand->siglock);
1490 	write_unlock_irq(&tasklist_lock);
1491 	proc_fork_connector(p);
1492 	cgroup_post_fork(p);
1493 	if (clone_flags & CLONE_THREAD)
1494 		threadgroup_change_end(current);
1495 	perf_event_fork(p);
1496 
1497 	trace_task_newtask(p, clone_flags);
1498 	uprobe_copy_process(p, clone_flags);
1499 
1500 	return p;
1501 
1502 bad_fork_free_pid:
1503 	if (pid != &init_struct_pid)
1504 		free_pid(pid);
1505 bad_fork_cleanup_io:
1506 	if (p->io_context)
1507 		exit_io_context(p);
1508 bad_fork_cleanup_namespaces:
1509 	exit_task_namespaces(p);
1510 bad_fork_cleanup_mm:
1511 	if (p->mm)
1512 		mmput(p->mm);
1513 bad_fork_cleanup_signal:
1514 	if (!(clone_flags & CLONE_THREAD))
1515 		free_signal_struct(p->signal);
1516 bad_fork_cleanup_sighand:
1517 	__cleanup_sighand(p->sighand);
1518 bad_fork_cleanup_fs:
1519 	exit_fs(p); /* blocking */
1520 bad_fork_cleanup_files:
1521 	exit_files(p); /* blocking */
1522 bad_fork_cleanup_semundo:
1523 	exit_sem(p);
1524 bad_fork_cleanup_audit:
1525 	audit_free(p);
1526 bad_fork_cleanup_policy:
1527 	perf_event_free_task(p);
1528 #ifdef CONFIG_NUMA
1529 	mpol_put(p->mempolicy);
1530 bad_fork_cleanup_threadgroup_lock:
1531 #endif
1532 	if (clone_flags & CLONE_THREAD)
1533 		threadgroup_change_end(current);
1534 	delayacct_tsk_free(p);
1535 	module_put(task_thread_info(p)->exec_domain->module);
1536 bad_fork_cleanup_count:
1537 	atomic_dec(&p->cred->user->processes);
1538 	exit_creds(p);
1539 bad_fork_free:
1540 	free_task(p);
1541 fork_out:
1542 	return ERR_PTR(retval);
1543 }
1544 
1545 static inline void init_idle_pids(struct pid_link *links)
1546 {
1547 	enum pid_type type;
1548 
1549 	for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1550 		INIT_HLIST_NODE(&links[type].node); /* not really needed */
1551 		links[type].pid = &init_struct_pid;
1552 	}
1553 }
1554 
1555 struct task_struct *fork_idle(int cpu)
1556 {
1557 	struct task_struct *task;
1558 	task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0);
1559 	if (!IS_ERR(task)) {
1560 		init_idle_pids(task->pids);
1561 		init_idle(task, cpu);
1562 	}
1563 
1564 	return task;
1565 }
1566 
1567 /*
1568  *  Ok, this is the main fork-routine.
1569  *
1570  * It copies the process, and if successful kick-starts
1571  * it and waits for it to finish using the VM if required.
1572  */
1573 long do_fork(unsigned long clone_flags,
1574 	      unsigned long stack_start,
1575 	      unsigned long stack_size,
1576 	      int __user *parent_tidptr,
1577 	      int __user *child_tidptr)
1578 {
1579 	struct task_struct *p;
1580 	int trace = 0;
1581 	long nr;
1582 
1583 	/*
1584 	 * Determine whether and which event to report to ptracer.  When
1585 	 * called from kernel_thread or CLONE_UNTRACED is explicitly
1586 	 * requested, no event is reported; otherwise, report if the event
1587 	 * for the type of forking is enabled.
1588 	 */
1589 	if (!(clone_flags & CLONE_UNTRACED)) {
1590 		if (clone_flags & CLONE_VFORK)
1591 			trace = PTRACE_EVENT_VFORK;
1592 		else if ((clone_flags & CSIGNAL) != SIGCHLD)
1593 			trace = PTRACE_EVENT_CLONE;
1594 		else
1595 			trace = PTRACE_EVENT_FORK;
1596 
1597 		if (likely(!ptrace_event_enabled(current, trace)))
1598 			trace = 0;
1599 	}
1600 
1601 	p = copy_process(clone_flags, stack_start, stack_size,
1602 			 child_tidptr, NULL, trace);
1603 	/*
1604 	 * Do this prior waking up the new thread - the thread pointer
1605 	 * might get invalid after that point, if the thread exits quickly.
1606 	 */
1607 	if (!IS_ERR(p)) {
1608 		struct completion vfork;
1609 
1610 		trace_sched_process_fork(current, p);
1611 
1612 		nr = task_pid_vnr(p);
1613 
1614 		if (clone_flags & CLONE_PARENT_SETTID)
1615 			put_user(nr, parent_tidptr);
1616 
1617 		if (clone_flags & CLONE_VFORK) {
1618 			p->vfork_done = &vfork;
1619 			init_completion(&vfork);
1620 			get_task_struct(p);
1621 		}
1622 
1623 		wake_up_new_task(p);
1624 
1625 		/* forking complete and child started to run, tell ptracer */
1626 		if (unlikely(trace))
1627 			ptrace_event(trace, nr);
1628 
1629 		if (clone_flags & CLONE_VFORK) {
1630 			if (!wait_for_vfork_done(p, &vfork))
1631 				ptrace_event(PTRACE_EVENT_VFORK_DONE, nr);
1632 		}
1633 	} else {
1634 		nr = PTR_ERR(p);
1635 	}
1636 	return nr;
1637 }
1638 
1639 /*
1640  * Create a kernel thread.
1641  */
1642 pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
1643 {
1644 	return do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
1645 		(unsigned long)arg, NULL, NULL);
1646 }
1647 
1648 #ifdef __ARCH_WANT_SYS_FORK
1649 SYSCALL_DEFINE0(fork)
1650 {
1651 #ifdef CONFIG_MMU
1652 	return do_fork(SIGCHLD, 0, 0, NULL, NULL);
1653 #else
1654 	/* can not support in nommu mode */
1655 	return -EINVAL;
1656 #endif
1657 }
1658 #endif
1659 
1660 #ifdef __ARCH_WANT_SYS_VFORK
1661 SYSCALL_DEFINE0(vfork)
1662 {
1663 	return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0,
1664 			0, NULL, NULL);
1665 }
1666 #endif
1667 
1668 #ifdef __ARCH_WANT_SYS_CLONE
1669 #ifdef CONFIG_CLONE_BACKWARDS
1670 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1671 		 int __user *, parent_tidptr,
1672 		 int, tls_val,
1673 		 int __user *, child_tidptr)
1674 #elif defined(CONFIG_CLONE_BACKWARDS2)
1675 SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
1676 		 int __user *, parent_tidptr,
1677 		 int __user *, child_tidptr,
1678 		 int, tls_val)
1679 #elif defined(CONFIG_CLONE_BACKWARDS3)
1680 SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
1681 		int, stack_size,
1682 		int __user *, parent_tidptr,
1683 		int __user *, child_tidptr,
1684 		int, tls_val)
1685 #else
1686 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1687 		 int __user *, parent_tidptr,
1688 		 int __user *, child_tidptr,
1689 		 int, tls_val)
1690 #endif
1691 {
1692 	return do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr);
1693 }
1694 #endif
1695 
1696 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1697 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1698 #endif
1699 
1700 static void sighand_ctor(void *data)
1701 {
1702 	struct sighand_struct *sighand = data;
1703 
1704 	spin_lock_init(&sighand->siglock);
1705 	init_waitqueue_head(&sighand->signalfd_wqh);
1706 }
1707 
1708 void __init proc_caches_init(void)
1709 {
1710 	sighand_cachep = kmem_cache_create("sighand_cache",
1711 			sizeof(struct sighand_struct), 0,
1712 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1713 			SLAB_NOTRACK, sighand_ctor);
1714 	signal_cachep = kmem_cache_create("signal_cache",
1715 			sizeof(struct signal_struct), 0,
1716 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1717 	files_cachep = kmem_cache_create("files_cache",
1718 			sizeof(struct files_struct), 0,
1719 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1720 	fs_cachep = kmem_cache_create("fs_cache",
1721 			sizeof(struct fs_struct), 0,
1722 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1723 	/*
1724 	 * FIXME! The "sizeof(struct mm_struct)" currently includes the
1725 	 * whole struct cpumask for the OFFSTACK case. We could change
1726 	 * this to *only* allocate as much of it as required by the
1727 	 * maximum number of CPU's we can ever have.  The cpumask_allocation
1728 	 * is at the end of the structure, exactly for that reason.
1729 	 */
1730 	mm_cachep = kmem_cache_create("mm_struct",
1731 			sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1732 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1733 	vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1734 	mmap_init();
1735 	nsproxy_cache_init();
1736 }
1737 
1738 /*
1739  * Check constraints on flags passed to the unshare system call.
1740  */
1741 static int check_unshare_flags(unsigned long unshare_flags)
1742 {
1743 	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1744 				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1745 				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
1746 				CLONE_NEWUSER|CLONE_NEWPID))
1747 		return -EINVAL;
1748 	/*
1749 	 * Not implemented, but pretend it works if there is nothing to
1750 	 * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
1751 	 * needs to unshare vm.
1752 	 */
1753 	if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
1754 		/* FIXME: get_task_mm() increments ->mm_users */
1755 		if (atomic_read(&current->mm->mm_users) > 1)
1756 			return -EINVAL;
1757 	}
1758 
1759 	return 0;
1760 }
1761 
1762 /*
1763  * Unshare the filesystem structure if it is being shared
1764  */
1765 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1766 {
1767 	struct fs_struct *fs = current->fs;
1768 
1769 	if (!(unshare_flags & CLONE_FS) || !fs)
1770 		return 0;
1771 
1772 	/* don't need lock here; in the worst case we'll do useless copy */
1773 	if (fs->users == 1)
1774 		return 0;
1775 
1776 	*new_fsp = copy_fs_struct(fs);
1777 	if (!*new_fsp)
1778 		return -ENOMEM;
1779 
1780 	return 0;
1781 }
1782 
1783 /*
1784  * Unshare file descriptor table if it is being shared
1785  */
1786 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1787 {
1788 	struct files_struct *fd = current->files;
1789 	int error = 0;
1790 
1791 	if ((unshare_flags & CLONE_FILES) &&
1792 	    (fd && atomic_read(&fd->count) > 1)) {
1793 		*new_fdp = dup_fd(fd, &error);
1794 		if (!*new_fdp)
1795 			return error;
1796 	}
1797 
1798 	return 0;
1799 }
1800 
1801 /*
1802  * unshare allows a process to 'unshare' part of the process
1803  * context which was originally shared using clone.  copy_*
1804  * functions used by do_fork() cannot be used here directly
1805  * because they modify an inactive task_struct that is being
1806  * constructed. Here we are modifying the current, active,
1807  * task_struct.
1808  */
1809 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1810 {
1811 	struct fs_struct *fs, *new_fs = NULL;
1812 	struct files_struct *fd, *new_fd = NULL;
1813 	struct cred *new_cred = NULL;
1814 	struct nsproxy *new_nsproxy = NULL;
1815 	int do_sysvsem = 0;
1816 	int err;
1817 
1818 	/*
1819 	 * If unsharing a user namespace must also unshare the thread.
1820 	 */
1821 	if (unshare_flags & CLONE_NEWUSER)
1822 		unshare_flags |= CLONE_THREAD | CLONE_FS;
1823 	/*
1824 	 * If unsharing a thread from a thread group, must also unshare vm.
1825 	 */
1826 	if (unshare_flags & CLONE_THREAD)
1827 		unshare_flags |= CLONE_VM;
1828 	/*
1829 	 * If unsharing vm, must also unshare signal handlers.
1830 	 */
1831 	if (unshare_flags & CLONE_VM)
1832 		unshare_flags |= CLONE_SIGHAND;
1833 	/*
1834 	 * If unsharing namespace, must also unshare filesystem information.
1835 	 */
1836 	if (unshare_flags & CLONE_NEWNS)
1837 		unshare_flags |= CLONE_FS;
1838 
1839 	err = check_unshare_flags(unshare_flags);
1840 	if (err)
1841 		goto bad_unshare_out;
1842 	/*
1843 	 * CLONE_NEWIPC must also detach from the undolist: after switching
1844 	 * to a new ipc namespace, the semaphore arrays from the old
1845 	 * namespace are unreachable.
1846 	 */
1847 	if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1848 		do_sysvsem = 1;
1849 	err = unshare_fs(unshare_flags, &new_fs);
1850 	if (err)
1851 		goto bad_unshare_out;
1852 	err = unshare_fd(unshare_flags, &new_fd);
1853 	if (err)
1854 		goto bad_unshare_cleanup_fs;
1855 	err = unshare_userns(unshare_flags, &new_cred);
1856 	if (err)
1857 		goto bad_unshare_cleanup_fd;
1858 	err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
1859 					 new_cred, new_fs);
1860 	if (err)
1861 		goto bad_unshare_cleanup_cred;
1862 
1863 	if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
1864 		if (do_sysvsem) {
1865 			/*
1866 			 * CLONE_SYSVSEM is equivalent to sys_exit().
1867 			 */
1868 			exit_sem(current);
1869 		}
1870 
1871 		if (new_nsproxy)
1872 			switch_task_namespaces(current, new_nsproxy);
1873 
1874 		task_lock(current);
1875 
1876 		if (new_fs) {
1877 			fs = current->fs;
1878 			spin_lock(&fs->lock);
1879 			current->fs = new_fs;
1880 			if (--fs->users)
1881 				new_fs = NULL;
1882 			else
1883 				new_fs = fs;
1884 			spin_unlock(&fs->lock);
1885 		}
1886 
1887 		if (new_fd) {
1888 			fd = current->files;
1889 			current->files = new_fd;
1890 			new_fd = fd;
1891 		}
1892 
1893 		task_unlock(current);
1894 
1895 		if (new_cred) {
1896 			/* Install the new user namespace */
1897 			commit_creds(new_cred);
1898 			new_cred = NULL;
1899 		}
1900 	}
1901 
1902 bad_unshare_cleanup_cred:
1903 	if (new_cred)
1904 		put_cred(new_cred);
1905 bad_unshare_cleanup_fd:
1906 	if (new_fd)
1907 		put_files_struct(new_fd);
1908 
1909 bad_unshare_cleanup_fs:
1910 	if (new_fs)
1911 		free_fs_struct(new_fs);
1912 
1913 bad_unshare_out:
1914 	return err;
1915 }
1916 
1917 /*
1918  *	Helper to unshare the files of the current task.
1919  *	We don't want to expose copy_files internals to
1920  *	the exec layer of the kernel.
1921  */
1922 
1923 int unshare_files(struct files_struct **displaced)
1924 {
1925 	struct task_struct *task = current;
1926 	struct files_struct *copy = NULL;
1927 	int error;
1928 
1929 	error = unshare_fd(CLONE_FILES, &copy);
1930 	if (error || !copy) {
1931 		*displaced = NULL;
1932 		return error;
1933 	}
1934 	*displaced = task->files;
1935 	task_lock(task);
1936 	task->files = copy;
1937 	task_unlock(task);
1938 	return 0;
1939 }
1940