xref: /openbmc/linux/kernel/fork.c (revision 5f32c314)
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/nsproxy.h>
32 #include <linux/capability.h>
33 #include <linux/cpu.h>
34 #include <linux/cgroup.h>
35 #include <linux/security.h>
36 #include <linux/hugetlb.h>
37 #include <linux/seccomp.h>
38 #include <linux/swap.h>
39 #include <linux/syscalls.h>
40 #include <linux/jiffies.h>
41 #include <linux/futex.h>
42 #include <linux/compat.h>
43 #include <linux/kthread.h>
44 #include <linux/task_io_accounting_ops.h>
45 #include <linux/rcupdate.h>
46 #include <linux/ptrace.h>
47 #include <linux/mount.h>
48 #include <linux/audit.h>
49 #include <linux/memcontrol.h>
50 #include <linux/ftrace.h>
51 #include <linux/proc_fs.h>
52 #include <linux/profile.h>
53 #include <linux/rmap.h>
54 #include <linux/ksm.h>
55 #include <linux/acct.h>
56 #include <linux/tsacct_kern.h>
57 #include <linux/cn_proc.h>
58 #include <linux/freezer.h>
59 #include <linux/delayacct.h>
60 #include <linux/taskstats_kern.h>
61 #include <linux/random.h>
62 #include <linux/tty.h>
63 #include <linux/blkdev.h>
64 #include <linux/fs_struct.h>
65 #include <linux/magic.h>
66 #include <linux/perf_event.h>
67 #include <linux/posix-timers.h>
68 #include <linux/user-return-notifier.h>
69 #include <linux/oom.h>
70 #include <linux/khugepaged.h>
71 #include <linux/signalfd.h>
72 #include <linux/uprobes.h>
73 #include <linux/aio.h>
74 
75 #include <asm/pgtable.h>
76 #include <asm/pgalloc.h>
77 #include <asm/uaccess.h>
78 #include <asm/mmu_context.h>
79 #include <asm/cacheflush.h>
80 #include <asm/tlbflush.h>
81 
82 #include <trace/events/sched.h>
83 
84 #define CREATE_TRACE_POINTS
85 #include <trace/events/task.h>
86 
87 /*
88  * Protected counters by write_lock_irq(&tasklist_lock)
89  */
90 unsigned long total_forks;	/* Handle normal Linux uptimes. */
91 int nr_threads;			/* The idle threads do not count.. */
92 
93 int max_threads;		/* tunable limit on nr_threads */
94 
95 DEFINE_PER_CPU(unsigned long, process_counts) = 0;
96 
97 __cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
98 
99 #ifdef CONFIG_PROVE_RCU
100 int lockdep_tasklist_lock_is_held(void)
101 {
102 	return lockdep_is_held(&tasklist_lock);
103 }
104 EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
105 #endif /* #ifdef CONFIG_PROVE_RCU */
106 
107 int nr_processes(void)
108 {
109 	int cpu;
110 	int total = 0;
111 
112 	for_each_possible_cpu(cpu)
113 		total += per_cpu(process_counts, cpu);
114 
115 	return total;
116 }
117 
118 void __weak arch_release_task_struct(struct task_struct *tsk)
119 {
120 }
121 
122 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
123 static struct kmem_cache *task_struct_cachep;
124 
125 static inline struct task_struct *alloc_task_struct_node(int node)
126 {
127 	return kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL, node);
128 }
129 
130 static inline void free_task_struct(struct task_struct *tsk)
131 {
132 	kmem_cache_free(task_struct_cachep, tsk);
133 }
134 #endif
135 
136 void __weak arch_release_thread_info(struct thread_info *ti)
137 {
138 }
139 
140 #ifndef CONFIG_ARCH_THREAD_INFO_ALLOCATOR
141 
142 /*
143  * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
144  * kmemcache based allocator.
145  */
146 # if THREAD_SIZE >= PAGE_SIZE
147 static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
148 						  int node)
149 {
150 	struct page *page = alloc_pages_node(node, THREADINFO_GFP_ACCOUNTED,
151 					     THREAD_SIZE_ORDER);
152 
153 	return page ? page_address(page) : NULL;
154 }
155 
156 static inline void free_thread_info(struct thread_info *ti)
157 {
158 	free_memcg_kmem_pages((unsigned long)ti, THREAD_SIZE_ORDER);
159 }
160 # else
161 static struct kmem_cache *thread_info_cache;
162 
163 static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
164 						  int node)
165 {
166 	return kmem_cache_alloc_node(thread_info_cache, THREADINFO_GFP, node);
167 }
168 
169 static void free_thread_info(struct thread_info *ti)
170 {
171 	kmem_cache_free(thread_info_cache, ti);
172 }
173 
174 void thread_info_cache_init(void)
175 {
176 	thread_info_cache = kmem_cache_create("thread_info", THREAD_SIZE,
177 					      THREAD_SIZE, 0, NULL);
178 	BUG_ON(thread_info_cache == NULL);
179 }
180 # endif
181 #endif
182 
183 /* SLAB cache for signal_struct structures (tsk->signal) */
184 static struct kmem_cache *signal_cachep;
185 
186 /* SLAB cache for sighand_struct structures (tsk->sighand) */
187 struct kmem_cache *sighand_cachep;
188 
189 /* SLAB cache for files_struct structures (tsk->files) */
190 struct kmem_cache *files_cachep;
191 
192 /* SLAB cache for fs_struct structures (tsk->fs) */
193 struct kmem_cache *fs_cachep;
194 
195 /* SLAB cache for vm_area_struct structures */
196 struct kmem_cache *vm_area_cachep;
197 
198 /* SLAB cache for mm_struct structures (tsk->mm) */
199 static struct kmem_cache *mm_cachep;
200 
201 static void account_kernel_stack(struct thread_info *ti, int account)
202 {
203 	struct zone *zone = page_zone(virt_to_page(ti));
204 
205 	mod_zone_page_state(zone, NR_KERNEL_STACK, account);
206 }
207 
208 void free_task(struct task_struct *tsk)
209 {
210 	account_kernel_stack(tsk->stack, -1);
211 	arch_release_thread_info(tsk->stack);
212 	free_thread_info(tsk->stack);
213 	rt_mutex_debug_task_free(tsk);
214 	ftrace_graph_exit_task(tsk);
215 	put_seccomp_filter(tsk);
216 	arch_release_task_struct(tsk);
217 	free_task_struct(tsk);
218 }
219 EXPORT_SYMBOL(free_task);
220 
221 static inline void free_signal_struct(struct signal_struct *sig)
222 {
223 	taskstats_tgid_free(sig);
224 	sched_autogroup_exit(sig);
225 	kmem_cache_free(signal_cachep, sig);
226 }
227 
228 static inline void put_signal_struct(struct signal_struct *sig)
229 {
230 	if (atomic_dec_and_test(&sig->sigcnt))
231 		free_signal_struct(sig);
232 }
233 
234 void __put_task_struct(struct task_struct *tsk)
235 {
236 	WARN_ON(!tsk->exit_state);
237 	WARN_ON(atomic_read(&tsk->usage));
238 	WARN_ON(tsk == current);
239 
240 	security_task_free(tsk);
241 	exit_creds(tsk);
242 	delayacct_tsk_free(tsk);
243 	put_signal_struct(tsk->signal);
244 
245 	if (!profile_handoff_task(tsk))
246 		free_task(tsk);
247 }
248 EXPORT_SYMBOL_GPL(__put_task_struct);
249 
250 void __init __weak arch_task_cache_init(void) { }
251 
252 void __init fork_init(unsigned long mempages)
253 {
254 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
255 #ifndef ARCH_MIN_TASKALIGN
256 #define ARCH_MIN_TASKALIGN	L1_CACHE_BYTES
257 #endif
258 	/* create a slab on which task_structs can be allocated */
259 	task_struct_cachep =
260 		kmem_cache_create("task_struct", sizeof(struct task_struct),
261 			ARCH_MIN_TASKALIGN, SLAB_PANIC | SLAB_NOTRACK, NULL);
262 #endif
263 
264 	/* do the arch specific task caches init */
265 	arch_task_cache_init();
266 
267 	/*
268 	 * The default maximum number of threads is set to a safe
269 	 * value: the thread structures can take up at most half
270 	 * of memory.
271 	 */
272 	max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
273 
274 	/*
275 	 * we need to allow at least 20 threads to boot a system
276 	 */
277 	if (max_threads < 20)
278 		max_threads = 20;
279 
280 	init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
281 	init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
282 	init_task.signal->rlim[RLIMIT_SIGPENDING] =
283 		init_task.signal->rlim[RLIMIT_NPROC];
284 }
285 
286 int __attribute__((weak)) arch_dup_task_struct(struct task_struct *dst,
287 					       struct task_struct *src)
288 {
289 	*dst = *src;
290 	return 0;
291 }
292 
293 static struct task_struct *dup_task_struct(struct task_struct *orig)
294 {
295 	struct task_struct *tsk;
296 	struct thread_info *ti;
297 	unsigned long *stackend;
298 	int node = tsk_fork_get_node(orig);
299 	int err;
300 
301 	tsk = alloc_task_struct_node(node);
302 	if (!tsk)
303 		return NULL;
304 
305 	ti = alloc_thread_info_node(tsk, node);
306 	if (!ti)
307 		goto free_tsk;
308 
309 	err = arch_dup_task_struct(tsk, orig);
310 	if (err)
311 		goto free_ti;
312 
313 	tsk->stack = ti;
314 
315 	setup_thread_stack(tsk, orig);
316 	clear_user_return_notifier(tsk);
317 	clear_tsk_need_resched(tsk);
318 	stackend = end_of_stack(tsk);
319 	*stackend = STACK_END_MAGIC;	/* for overflow detection */
320 
321 #ifdef CONFIG_CC_STACKPROTECTOR
322 	tsk->stack_canary = get_random_int();
323 #endif
324 
325 	/*
326 	 * One for us, one for whoever does the "release_task()" (usually
327 	 * parent)
328 	 */
329 	atomic_set(&tsk->usage, 2);
330 #ifdef CONFIG_BLK_DEV_IO_TRACE
331 	tsk->btrace_seq = 0;
332 #endif
333 	tsk->splice_pipe = NULL;
334 	tsk->task_frag.page = NULL;
335 
336 	account_kernel_stack(ti, 1);
337 
338 	return tsk;
339 
340 free_ti:
341 	free_thread_info(ti);
342 free_tsk:
343 	free_task_struct(tsk);
344 	return NULL;
345 }
346 
347 #ifdef CONFIG_MMU
348 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
349 {
350 	struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
351 	struct rb_node **rb_link, *rb_parent;
352 	int retval;
353 	unsigned long charge;
354 
355 	uprobe_start_dup_mmap();
356 	down_write(&oldmm->mmap_sem);
357 	flush_cache_dup_mm(oldmm);
358 	uprobe_dup_mmap(oldmm, mm);
359 	/*
360 	 * Not linked in yet - no deadlock potential:
361 	 */
362 	down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
363 
364 	mm->locked_vm = 0;
365 	mm->mmap = NULL;
366 	mm->mmap_cache = NULL;
367 	mm->map_count = 0;
368 	cpumask_clear(mm_cpumask(mm));
369 	mm->mm_rb = RB_ROOT;
370 	rb_link = &mm->mm_rb.rb_node;
371 	rb_parent = NULL;
372 	pprev = &mm->mmap;
373 	retval = ksm_fork(mm, oldmm);
374 	if (retval)
375 		goto out;
376 	retval = khugepaged_fork(mm, oldmm);
377 	if (retval)
378 		goto out;
379 
380 	prev = NULL;
381 	for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
382 		struct file *file;
383 
384 		if (mpnt->vm_flags & VM_DONTCOPY) {
385 			vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
386 							-vma_pages(mpnt));
387 			continue;
388 		}
389 		charge = 0;
390 		if (mpnt->vm_flags & VM_ACCOUNT) {
391 			unsigned long len = vma_pages(mpnt);
392 
393 			if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
394 				goto fail_nomem;
395 			charge = len;
396 		}
397 		tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
398 		if (!tmp)
399 			goto fail_nomem;
400 		*tmp = *mpnt;
401 		INIT_LIST_HEAD(&tmp->anon_vma_chain);
402 		retval = vma_dup_policy(mpnt, tmp);
403 		if (retval)
404 			goto fail_nomem_policy;
405 		tmp->vm_mm = mm;
406 		if (anon_vma_fork(tmp, mpnt))
407 			goto fail_nomem_anon_vma_fork;
408 		tmp->vm_flags &= ~VM_LOCKED;
409 		tmp->vm_next = tmp->vm_prev = NULL;
410 		file = tmp->vm_file;
411 		if (file) {
412 			struct inode *inode = file_inode(file);
413 			struct address_space *mapping = file->f_mapping;
414 
415 			get_file(file);
416 			if (tmp->vm_flags & VM_DENYWRITE)
417 				atomic_dec(&inode->i_writecount);
418 			mutex_lock(&mapping->i_mmap_mutex);
419 			if (tmp->vm_flags & VM_SHARED)
420 				mapping->i_mmap_writable++;
421 			flush_dcache_mmap_lock(mapping);
422 			/* insert tmp into the share list, just after mpnt */
423 			if (unlikely(tmp->vm_flags & VM_NONLINEAR))
424 				vma_nonlinear_insert(tmp,
425 						&mapping->i_mmap_nonlinear);
426 			else
427 				vma_interval_tree_insert_after(tmp, mpnt,
428 							&mapping->i_mmap);
429 			flush_dcache_mmap_unlock(mapping);
430 			mutex_unlock(&mapping->i_mmap_mutex);
431 		}
432 
433 		/*
434 		 * Clear hugetlb-related page reserves for children. This only
435 		 * affects MAP_PRIVATE mappings. Faults generated by the child
436 		 * are not guaranteed to succeed, even if read-only
437 		 */
438 		if (is_vm_hugetlb_page(tmp))
439 			reset_vma_resv_huge_pages(tmp);
440 
441 		/*
442 		 * Link in the new vma and copy the page table entries.
443 		 */
444 		*pprev = tmp;
445 		pprev = &tmp->vm_next;
446 		tmp->vm_prev = prev;
447 		prev = tmp;
448 
449 		__vma_link_rb(mm, tmp, rb_link, rb_parent);
450 		rb_link = &tmp->vm_rb.rb_right;
451 		rb_parent = &tmp->vm_rb;
452 
453 		mm->map_count++;
454 		retval = copy_page_range(mm, oldmm, mpnt);
455 
456 		if (tmp->vm_ops && tmp->vm_ops->open)
457 			tmp->vm_ops->open(tmp);
458 
459 		if (retval)
460 			goto out;
461 	}
462 	/* a new mm has just been created */
463 	arch_dup_mmap(oldmm, mm);
464 	retval = 0;
465 out:
466 	up_write(&mm->mmap_sem);
467 	flush_tlb_mm(oldmm);
468 	up_write(&oldmm->mmap_sem);
469 	uprobe_end_dup_mmap();
470 	return retval;
471 fail_nomem_anon_vma_fork:
472 	mpol_put(vma_policy(tmp));
473 fail_nomem_policy:
474 	kmem_cache_free(vm_area_cachep, tmp);
475 fail_nomem:
476 	retval = -ENOMEM;
477 	vm_unacct_memory(charge);
478 	goto out;
479 }
480 
481 static inline int mm_alloc_pgd(struct mm_struct *mm)
482 {
483 	mm->pgd = pgd_alloc(mm);
484 	if (unlikely(!mm->pgd))
485 		return -ENOMEM;
486 	return 0;
487 }
488 
489 static inline void mm_free_pgd(struct mm_struct *mm)
490 {
491 	pgd_free(mm, mm->pgd);
492 }
493 #else
494 #define dup_mmap(mm, oldmm)	(0)
495 #define mm_alloc_pgd(mm)	(0)
496 #define mm_free_pgd(mm)
497 #endif /* CONFIG_MMU */
498 
499 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
500 
501 #define allocate_mm()	(kmem_cache_alloc(mm_cachep, GFP_KERNEL))
502 #define free_mm(mm)	(kmem_cache_free(mm_cachep, (mm)))
503 
504 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
505 
506 static int __init coredump_filter_setup(char *s)
507 {
508 	default_dump_filter =
509 		(simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
510 		MMF_DUMP_FILTER_MASK;
511 	return 1;
512 }
513 
514 __setup("coredump_filter=", coredump_filter_setup);
515 
516 #include <linux/init_task.h>
517 
518 static void mm_init_aio(struct mm_struct *mm)
519 {
520 #ifdef CONFIG_AIO
521 	spin_lock_init(&mm->ioctx_lock);
522 	mm->ioctx_table = NULL;
523 #endif
524 }
525 
526 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
527 {
528 	atomic_set(&mm->mm_users, 1);
529 	atomic_set(&mm->mm_count, 1);
530 	init_rwsem(&mm->mmap_sem);
531 	INIT_LIST_HEAD(&mm->mmlist);
532 	mm->flags = (current->mm) ?
533 		(current->mm->flags & MMF_INIT_MASK) : default_dump_filter;
534 	mm->core_state = NULL;
535 	atomic_long_set(&mm->nr_ptes, 0);
536 	memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
537 	spin_lock_init(&mm->page_table_lock);
538 	mm_init_aio(mm);
539 	mm_init_owner(mm, p);
540 	clear_tlb_flush_pending(mm);
541 
542 	if (likely(!mm_alloc_pgd(mm))) {
543 		mm->def_flags = 0;
544 		mmu_notifier_mm_init(mm);
545 		return mm;
546 	}
547 
548 	free_mm(mm);
549 	return NULL;
550 }
551 
552 static void check_mm(struct mm_struct *mm)
553 {
554 	int i;
555 
556 	for (i = 0; i < NR_MM_COUNTERS; i++) {
557 		long x = atomic_long_read(&mm->rss_stat.count[i]);
558 
559 		if (unlikely(x))
560 			printk(KERN_ALERT "BUG: Bad rss-counter state "
561 					  "mm:%p idx:%d val:%ld\n", mm, i, x);
562 	}
563 
564 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
565 	VM_BUG_ON(mm->pmd_huge_pte);
566 #endif
567 }
568 
569 /*
570  * Allocate and initialize an mm_struct.
571  */
572 struct mm_struct *mm_alloc(void)
573 {
574 	struct mm_struct *mm;
575 
576 	mm = allocate_mm();
577 	if (!mm)
578 		return NULL;
579 
580 	memset(mm, 0, sizeof(*mm));
581 	mm_init_cpumask(mm);
582 	return mm_init(mm, current);
583 }
584 
585 /*
586  * Called when the last reference to the mm
587  * is dropped: either by a lazy thread or by
588  * mmput. Free the page directory and the mm.
589  */
590 void __mmdrop(struct mm_struct *mm)
591 {
592 	BUG_ON(mm == &init_mm);
593 	mm_free_pgd(mm);
594 	destroy_context(mm);
595 	mmu_notifier_mm_destroy(mm);
596 	check_mm(mm);
597 	free_mm(mm);
598 }
599 EXPORT_SYMBOL_GPL(__mmdrop);
600 
601 /*
602  * Decrement the use count and release all resources for an mm.
603  */
604 void mmput(struct mm_struct *mm)
605 {
606 	might_sleep();
607 
608 	if (atomic_dec_and_test(&mm->mm_users)) {
609 		uprobe_clear_state(mm);
610 		exit_aio(mm);
611 		ksm_exit(mm);
612 		khugepaged_exit(mm); /* must run before exit_mmap */
613 		exit_mmap(mm);
614 		set_mm_exe_file(mm, NULL);
615 		if (!list_empty(&mm->mmlist)) {
616 			spin_lock(&mmlist_lock);
617 			list_del(&mm->mmlist);
618 			spin_unlock(&mmlist_lock);
619 		}
620 		if (mm->binfmt)
621 			module_put(mm->binfmt->module);
622 		mmdrop(mm);
623 	}
624 }
625 EXPORT_SYMBOL_GPL(mmput);
626 
627 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
628 {
629 	if (new_exe_file)
630 		get_file(new_exe_file);
631 	if (mm->exe_file)
632 		fput(mm->exe_file);
633 	mm->exe_file = new_exe_file;
634 }
635 
636 struct file *get_mm_exe_file(struct mm_struct *mm)
637 {
638 	struct file *exe_file;
639 
640 	/* We need mmap_sem to protect against races with removal of exe_file */
641 	down_read(&mm->mmap_sem);
642 	exe_file = mm->exe_file;
643 	if (exe_file)
644 		get_file(exe_file);
645 	up_read(&mm->mmap_sem);
646 	return exe_file;
647 }
648 
649 static void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
650 {
651 	/* It's safe to write the exe_file pointer without exe_file_lock because
652 	 * this is called during fork when the task is not yet in /proc */
653 	newmm->exe_file = get_mm_exe_file(oldmm);
654 }
655 
656 /**
657  * get_task_mm - acquire a reference to the task's mm
658  *
659  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
660  * this kernel workthread has transiently adopted a user mm with use_mm,
661  * to do its AIO) is not set and if so returns a reference to it, after
662  * bumping up the use count.  User must release the mm via mmput()
663  * after use.  Typically used by /proc and ptrace.
664  */
665 struct mm_struct *get_task_mm(struct task_struct *task)
666 {
667 	struct mm_struct *mm;
668 
669 	task_lock(task);
670 	mm = task->mm;
671 	if (mm) {
672 		if (task->flags & PF_KTHREAD)
673 			mm = NULL;
674 		else
675 			atomic_inc(&mm->mm_users);
676 	}
677 	task_unlock(task);
678 	return mm;
679 }
680 EXPORT_SYMBOL_GPL(get_task_mm);
681 
682 struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
683 {
684 	struct mm_struct *mm;
685 	int err;
686 
687 	err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
688 	if (err)
689 		return ERR_PTR(err);
690 
691 	mm = get_task_mm(task);
692 	if (mm && mm != current->mm &&
693 			!ptrace_may_access(task, mode)) {
694 		mmput(mm);
695 		mm = ERR_PTR(-EACCES);
696 	}
697 	mutex_unlock(&task->signal->cred_guard_mutex);
698 
699 	return mm;
700 }
701 
702 static void complete_vfork_done(struct task_struct *tsk)
703 {
704 	struct completion *vfork;
705 
706 	task_lock(tsk);
707 	vfork = tsk->vfork_done;
708 	if (likely(vfork)) {
709 		tsk->vfork_done = NULL;
710 		complete(vfork);
711 	}
712 	task_unlock(tsk);
713 }
714 
715 static int wait_for_vfork_done(struct task_struct *child,
716 				struct completion *vfork)
717 {
718 	int killed;
719 
720 	freezer_do_not_count();
721 	killed = wait_for_completion_killable(vfork);
722 	freezer_count();
723 
724 	if (killed) {
725 		task_lock(child);
726 		child->vfork_done = NULL;
727 		task_unlock(child);
728 	}
729 
730 	put_task_struct(child);
731 	return killed;
732 }
733 
734 /* Please note the differences between mmput and mm_release.
735  * mmput is called whenever we stop holding onto a mm_struct,
736  * error success whatever.
737  *
738  * mm_release is called after a mm_struct has been removed
739  * from the current process.
740  *
741  * This difference is important for error handling, when we
742  * only half set up a mm_struct for a new process and need to restore
743  * the old one.  Because we mmput the new mm_struct before
744  * restoring the old one. . .
745  * Eric Biederman 10 January 1998
746  */
747 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
748 {
749 	/* Get rid of any futexes when releasing the mm */
750 #ifdef CONFIG_FUTEX
751 	if (unlikely(tsk->robust_list)) {
752 		exit_robust_list(tsk);
753 		tsk->robust_list = NULL;
754 	}
755 #ifdef CONFIG_COMPAT
756 	if (unlikely(tsk->compat_robust_list)) {
757 		compat_exit_robust_list(tsk);
758 		tsk->compat_robust_list = NULL;
759 	}
760 #endif
761 	if (unlikely(!list_empty(&tsk->pi_state_list)))
762 		exit_pi_state_list(tsk);
763 #endif
764 
765 	uprobe_free_utask(tsk);
766 
767 	/* Get rid of any cached register state */
768 	deactivate_mm(tsk, mm);
769 
770 	/*
771 	 * If we're exiting normally, clear a user-space tid field if
772 	 * requested.  We leave this alone when dying by signal, to leave
773 	 * the value intact in a core dump, and to save the unnecessary
774 	 * trouble, say, a killed vfork parent shouldn't touch this mm.
775 	 * Userland only wants this done for a sys_exit.
776 	 */
777 	if (tsk->clear_child_tid) {
778 		if (!(tsk->flags & PF_SIGNALED) &&
779 		    atomic_read(&mm->mm_users) > 1) {
780 			/*
781 			 * We don't check the error code - if userspace has
782 			 * not set up a proper pointer then tough luck.
783 			 */
784 			put_user(0, tsk->clear_child_tid);
785 			sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
786 					1, NULL, NULL, 0);
787 		}
788 		tsk->clear_child_tid = NULL;
789 	}
790 
791 	/*
792 	 * All done, finally we can wake up parent and return this mm to him.
793 	 * Also kthread_stop() uses this completion for synchronization.
794 	 */
795 	if (tsk->vfork_done)
796 		complete_vfork_done(tsk);
797 }
798 
799 /*
800  * Allocate a new mm structure and copy contents from the
801  * mm structure of the passed in task structure.
802  */
803 static struct mm_struct *dup_mm(struct task_struct *tsk)
804 {
805 	struct mm_struct *mm, *oldmm = current->mm;
806 	int err;
807 
808 	mm = allocate_mm();
809 	if (!mm)
810 		goto fail_nomem;
811 
812 	memcpy(mm, oldmm, sizeof(*mm));
813 	mm_init_cpumask(mm);
814 
815 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
816 	mm->pmd_huge_pte = NULL;
817 #endif
818 	if (!mm_init(mm, tsk))
819 		goto fail_nomem;
820 
821 	if (init_new_context(tsk, mm))
822 		goto fail_nocontext;
823 
824 	dup_mm_exe_file(oldmm, mm);
825 
826 	err = dup_mmap(mm, oldmm);
827 	if (err)
828 		goto free_pt;
829 
830 	mm->hiwater_rss = get_mm_rss(mm);
831 	mm->hiwater_vm = mm->total_vm;
832 
833 	if (mm->binfmt && !try_module_get(mm->binfmt->module))
834 		goto free_pt;
835 
836 	return mm;
837 
838 free_pt:
839 	/* don't put binfmt in mmput, we haven't got module yet */
840 	mm->binfmt = NULL;
841 	mmput(mm);
842 
843 fail_nomem:
844 	return NULL;
845 
846 fail_nocontext:
847 	/*
848 	 * If init_new_context() failed, we cannot use mmput() to free the mm
849 	 * because it calls destroy_context()
850 	 */
851 	mm_free_pgd(mm);
852 	free_mm(mm);
853 	return NULL;
854 }
855 
856 static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
857 {
858 	struct mm_struct *mm, *oldmm;
859 	int retval;
860 
861 	tsk->min_flt = tsk->maj_flt = 0;
862 	tsk->nvcsw = tsk->nivcsw = 0;
863 #ifdef CONFIG_DETECT_HUNG_TASK
864 	tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
865 #endif
866 
867 	tsk->mm = NULL;
868 	tsk->active_mm = NULL;
869 
870 	/*
871 	 * Are we cloning a kernel thread?
872 	 *
873 	 * We need to steal a active VM for that..
874 	 */
875 	oldmm = current->mm;
876 	if (!oldmm)
877 		return 0;
878 
879 	if (clone_flags & CLONE_VM) {
880 		atomic_inc(&oldmm->mm_users);
881 		mm = oldmm;
882 		goto good_mm;
883 	}
884 
885 	retval = -ENOMEM;
886 	mm = dup_mm(tsk);
887 	if (!mm)
888 		goto fail_nomem;
889 
890 good_mm:
891 	tsk->mm = mm;
892 	tsk->active_mm = mm;
893 	return 0;
894 
895 fail_nomem:
896 	return retval;
897 }
898 
899 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
900 {
901 	struct fs_struct *fs = current->fs;
902 	if (clone_flags & CLONE_FS) {
903 		/* tsk->fs is already what we want */
904 		spin_lock(&fs->lock);
905 		if (fs->in_exec) {
906 			spin_unlock(&fs->lock);
907 			return -EAGAIN;
908 		}
909 		fs->users++;
910 		spin_unlock(&fs->lock);
911 		return 0;
912 	}
913 	tsk->fs = copy_fs_struct(fs);
914 	if (!tsk->fs)
915 		return -ENOMEM;
916 	return 0;
917 }
918 
919 static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
920 {
921 	struct files_struct *oldf, *newf;
922 	int error = 0;
923 
924 	/*
925 	 * A background process may not have any files ...
926 	 */
927 	oldf = current->files;
928 	if (!oldf)
929 		goto out;
930 
931 	if (clone_flags & CLONE_FILES) {
932 		atomic_inc(&oldf->count);
933 		goto out;
934 	}
935 
936 	newf = dup_fd(oldf, &error);
937 	if (!newf)
938 		goto out;
939 
940 	tsk->files = newf;
941 	error = 0;
942 out:
943 	return error;
944 }
945 
946 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
947 {
948 #ifdef CONFIG_BLOCK
949 	struct io_context *ioc = current->io_context;
950 	struct io_context *new_ioc;
951 
952 	if (!ioc)
953 		return 0;
954 	/*
955 	 * Share io context with parent, if CLONE_IO is set
956 	 */
957 	if (clone_flags & CLONE_IO) {
958 		ioc_task_link(ioc);
959 		tsk->io_context = ioc;
960 	} else if (ioprio_valid(ioc->ioprio)) {
961 		new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
962 		if (unlikely(!new_ioc))
963 			return -ENOMEM;
964 
965 		new_ioc->ioprio = ioc->ioprio;
966 		put_io_context(new_ioc);
967 	}
968 #endif
969 	return 0;
970 }
971 
972 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
973 {
974 	struct sighand_struct *sig;
975 
976 	if (clone_flags & CLONE_SIGHAND) {
977 		atomic_inc(&current->sighand->count);
978 		return 0;
979 	}
980 	sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
981 	rcu_assign_pointer(tsk->sighand, sig);
982 	if (!sig)
983 		return -ENOMEM;
984 	atomic_set(&sig->count, 1);
985 	memcpy(sig->action, current->sighand->action, sizeof(sig->action));
986 	return 0;
987 }
988 
989 void __cleanup_sighand(struct sighand_struct *sighand)
990 {
991 	if (atomic_dec_and_test(&sighand->count)) {
992 		signalfd_cleanup(sighand);
993 		kmem_cache_free(sighand_cachep, sighand);
994 	}
995 }
996 
997 
998 /*
999  * Initialize POSIX timer handling for a thread group.
1000  */
1001 static void posix_cpu_timers_init_group(struct signal_struct *sig)
1002 {
1003 	unsigned long cpu_limit;
1004 
1005 	/* Thread group counters. */
1006 	thread_group_cputime_init(sig);
1007 
1008 	cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1009 	if (cpu_limit != RLIM_INFINITY) {
1010 		sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
1011 		sig->cputimer.running = 1;
1012 	}
1013 
1014 	/* The timer lists. */
1015 	INIT_LIST_HEAD(&sig->cpu_timers[0]);
1016 	INIT_LIST_HEAD(&sig->cpu_timers[1]);
1017 	INIT_LIST_HEAD(&sig->cpu_timers[2]);
1018 }
1019 
1020 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1021 {
1022 	struct signal_struct *sig;
1023 
1024 	if (clone_flags & CLONE_THREAD)
1025 		return 0;
1026 
1027 	sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1028 	tsk->signal = sig;
1029 	if (!sig)
1030 		return -ENOMEM;
1031 
1032 	sig->nr_threads = 1;
1033 	atomic_set(&sig->live, 1);
1034 	atomic_set(&sig->sigcnt, 1);
1035 
1036 	/* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */
1037 	sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node);
1038 	tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);
1039 
1040 	init_waitqueue_head(&sig->wait_chldexit);
1041 	sig->curr_target = tsk;
1042 	init_sigpending(&sig->shared_pending);
1043 	INIT_LIST_HEAD(&sig->posix_timers);
1044 
1045 	hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1046 	sig->real_timer.function = it_real_fn;
1047 
1048 	task_lock(current->group_leader);
1049 	memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1050 	task_unlock(current->group_leader);
1051 
1052 	posix_cpu_timers_init_group(sig);
1053 
1054 	tty_audit_fork(sig);
1055 	sched_autogroup_fork(sig);
1056 
1057 #ifdef CONFIG_CGROUPS
1058 	init_rwsem(&sig->group_rwsem);
1059 #endif
1060 
1061 	sig->oom_score_adj = current->signal->oom_score_adj;
1062 	sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1063 
1064 	sig->has_child_subreaper = current->signal->has_child_subreaper ||
1065 				   current->signal->is_child_subreaper;
1066 
1067 	mutex_init(&sig->cred_guard_mutex);
1068 
1069 	return 0;
1070 }
1071 
1072 static void copy_flags(unsigned long clone_flags, struct task_struct *p)
1073 {
1074 	unsigned long new_flags = p->flags;
1075 
1076 	new_flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
1077 	new_flags |= PF_FORKNOEXEC;
1078 	p->flags = new_flags;
1079 }
1080 
1081 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1082 {
1083 	current->clear_child_tid = tidptr;
1084 
1085 	return task_pid_vnr(current);
1086 }
1087 
1088 static void rt_mutex_init_task(struct task_struct *p)
1089 {
1090 	raw_spin_lock_init(&p->pi_lock);
1091 #ifdef CONFIG_RT_MUTEXES
1092 	p->pi_waiters = RB_ROOT;
1093 	p->pi_waiters_leftmost = NULL;
1094 	p->pi_blocked_on = NULL;
1095 	p->pi_top_task = NULL;
1096 #endif
1097 }
1098 
1099 #ifdef CONFIG_MM_OWNER
1100 void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
1101 {
1102 	mm->owner = p;
1103 }
1104 #endif /* CONFIG_MM_OWNER */
1105 
1106 /*
1107  * Initialize POSIX timer handling for a single task.
1108  */
1109 static void posix_cpu_timers_init(struct task_struct *tsk)
1110 {
1111 	tsk->cputime_expires.prof_exp = 0;
1112 	tsk->cputime_expires.virt_exp = 0;
1113 	tsk->cputime_expires.sched_exp = 0;
1114 	INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1115 	INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1116 	INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1117 }
1118 
1119 static inline void
1120 init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
1121 {
1122 	 task->pids[type].pid = pid;
1123 }
1124 
1125 /*
1126  * This creates a new process as a copy of the old one,
1127  * but does not actually start it yet.
1128  *
1129  * It copies the registers, and all the appropriate
1130  * parts of the process environment (as per the clone
1131  * flags). The actual kick-off is left to the caller.
1132  */
1133 static struct task_struct *copy_process(unsigned long clone_flags,
1134 					unsigned long stack_start,
1135 					unsigned long stack_size,
1136 					int __user *child_tidptr,
1137 					struct pid *pid,
1138 					int trace)
1139 {
1140 	int retval;
1141 	struct task_struct *p;
1142 
1143 	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1144 		return ERR_PTR(-EINVAL);
1145 
1146 	if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
1147 		return ERR_PTR(-EINVAL);
1148 
1149 	/*
1150 	 * Thread groups must share signals as well, and detached threads
1151 	 * can only be started up within the thread group.
1152 	 */
1153 	if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1154 		return ERR_PTR(-EINVAL);
1155 
1156 	/*
1157 	 * Shared signal handlers imply shared VM. By way of the above,
1158 	 * thread groups also imply shared VM. Blocking this case allows
1159 	 * for various simplifications in other code.
1160 	 */
1161 	if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1162 		return ERR_PTR(-EINVAL);
1163 
1164 	/*
1165 	 * Siblings of global init remain as zombies on exit since they are
1166 	 * not reaped by their parent (swapper). To solve this and to avoid
1167 	 * multi-rooted process trees, prevent global and container-inits
1168 	 * from creating siblings.
1169 	 */
1170 	if ((clone_flags & CLONE_PARENT) &&
1171 				current->signal->flags & SIGNAL_UNKILLABLE)
1172 		return ERR_PTR(-EINVAL);
1173 
1174 	/*
1175 	 * If the new process will be in a different pid or user namespace
1176 	 * do not allow it to share a thread group or signal handlers or
1177 	 * parent with the forking task.
1178 	 */
1179 	if (clone_flags & CLONE_SIGHAND) {
1180 		if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
1181 		    (task_active_pid_ns(current) !=
1182 				current->nsproxy->pid_ns_for_children))
1183 			return ERR_PTR(-EINVAL);
1184 	}
1185 
1186 	retval = security_task_create(clone_flags);
1187 	if (retval)
1188 		goto fork_out;
1189 
1190 	retval = -ENOMEM;
1191 	p = dup_task_struct(current);
1192 	if (!p)
1193 		goto fork_out;
1194 
1195 	ftrace_graph_init_task(p);
1196 	get_seccomp_filter(p);
1197 
1198 	rt_mutex_init_task(p);
1199 
1200 #ifdef CONFIG_PROVE_LOCKING
1201 	DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1202 	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1203 #endif
1204 	retval = -EAGAIN;
1205 	if (atomic_read(&p->real_cred->user->processes) >=
1206 			task_rlimit(p, RLIMIT_NPROC)) {
1207 		if (p->real_cred->user != INIT_USER &&
1208 		    !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
1209 			goto bad_fork_free;
1210 	}
1211 	current->flags &= ~PF_NPROC_EXCEEDED;
1212 
1213 	retval = copy_creds(p, clone_flags);
1214 	if (retval < 0)
1215 		goto bad_fork_free;
1216 
1217 	/*
1218 	 * If multiple threads are within copy_process(), then this check
1219 	 * triggers too late. This doesn't hurt, the check is only there
1220 	 * to stop root fork bombs.
1221 	 */
1222 	retval = -EAGAIN;
1223 	if (nr_threads >= max_threads)
1224 		goto bad_fork_cleanup_count;
1225 
1226 	if (!try_module_get(task_thread_info(p)->exec_domain->module))
1227 		goto bad_fork_cleanup_count;
1228 
1229 	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */
1230 	copy_flags(clone_flags, p);
1231 	INIT_LIST_HEAD(&p->children);
1232 	INIT_LIST_HEAD(&p->sibling);
1233 	rcu_copy_process(p);
1234 	p->vfork_done = NULL;
1235 	spin_lock_init(&p->alloc_lock);
1236 
1237 	init_sigpending(&p->pending);
1238 
1239 	p->utime = p->stime = p->gtime = 0;
1240 	p->utimescaled = p->stimescaled = 0;
1241 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
1242 	p->prev_cputime.utime = p->prev_cputime.stime = 0;
1243 #endif
1244 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
1245 	seqlock_init(&p->vtime_seqlock);
1246 	p->vtime_snap = 0;
1247 	p->vtime_snap_whence = VTIME_SLEEPING;
1248 #endif
1249 
1250 #if defined(SPLIT_RSS_COUNTING)
1251 	memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1252 #endif
1253 
1254 	p->default_timer_slack_ns = current->timer_slack_ns;
1255 
1256 	task_io_accounting_init(&p->ioac);
1257 	acct_clear_integrals(p);
1258 
1259 	posix_cpu_timers_init(p);
1260 
1261 	do_posix_clock_monotonic_gettime(&p->start_time);
1262 	p->real_start_time = p->start_time;
1263 	monotonic_to_bootbased(&p->real_start_time);
1264 	p->io_context = NULL;
1265 	p->audit_context = NULL;
1266 	if (clone_flags & CLONE_THREAD)
1267 		threadgroup_change_begin(current);
1268 	cgroup_fork(p);
1269 #ifdef CONFIG_NUMA
1270 	p->mempolicy = mpol_dup(p->mempolicy);
1271 	if (IS_ERR(p->mempolicy)) {
1272 		retval = PTR_ERR(p->mempolicy);
1273 		p->mempolicy = NULL;
1274 		goto bad_fork_cleanup_cgroup;
1275 	}
1276 	mpol_fix_fork_child_flag(p);
1277 #endif
1278 #ifdef CONFIG_CPUSETS
1279 	p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
1280 	p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
1281 	seqcount_init(&p->mems_allowed_seq);
1282 #endif
1283 #ifdef CONFIG_TRACE_IRQFLAGS
1284 	p->irq_events = 0;
1285 	p->hardirqs_enabled = 0;
1286 	p->hardirq_enable_ip = 0;
1287 	p->hardirq_enable_event = 0;
1288 	p->hardirq_disable_ip = _THIS_IP_;
1289 	p->hardirq_disable_event = 0;
1290 	p->softirqs_enabled = 1;
1291 	p->softirq_enable_ip = _THIS_IP_;
1292 	p->softirq_enable_event = 0;
1293 	p->softirq_disable_ip = 0;
1294 	p->softirq_disable_event = 0;
1295 	p->hardirq_context = 0;
1296 	p->softirq_context = 0;
1297 #endif
1298 #ifdef CONFIG_LOCKDEP
1299 	p->lockdep_depth = 0; /* no locks held yet */
1300 	p->curr_chain_key = 0;
1301 	p->lockdep_recursion = 0;
1302 #endif
1303 
1304 #ifdef CONFIG_DEBUG_MUTEXES
1305 	p->blocked_on = NULL; /* not blocked yet */
1306 #endif
1307 #ifdef CONFIG_MEMCG
1308 	p->memcg_batch.do_batch = 0;
1309 	p->memcg_batch.memcg = NULL;
1310 #endif
1311 #ifdef CONFIG_BCACHE
1312 	p->sequential_io	= 0;
1313 	p->sequential_io_avg	= 0;
1314 #endif
1315 
1316 	/* Perform scheduler related setup. Assign this task to a CPU. */
1317 	retval = sched_fork(clone_flags, p);
1318 	if (retval)
1319 		goto bad_fork_cleanup_policy;
1320 
1321 	retval = perf_event_init_task(p);
1322 	if (retval)
1323 		goto bad_fork_cleanup_policy;
1324 	retval = audit_alloc(p);
1325 	if (retval)
1326 		goto bad_fork_cleanup_policy;
1327 	/* copy all the process information */
1328 	retval = copy_semundo(clone_flags, p);
1329 	if (retval)
1330 		goto bad_fork_cleanup_audit;
1331 	retval = copy_files(clone_flags, p);
1332 	if (retval)
1333 		goto bad_fork_cleanup_semundo;
1334 	retval = copy_fs(clone_flags, p);
1335 	if (retval)
1336 		goto bad_fork_cleanup_files;
1337 	retval = copy_sighand(clone_flags, p);
1338 	if (retval)
1339 		goto bad_fork_cleanup_fs;
1340 	retval = copy_signal(clone_flags, p);
1341 	if (retval)
1342 		goto bad_fork_cleanup_sighand;
1343 	retval = copy_mm(clone_flags, p);
1344 	if (retval)
1345 		goto bad_fork_cleanup_signal;
1346 	retval = copy_namespaces(clone_flags, p);
1347 	if (retval)
1348 		goto bad_fork_cleanup_mm;
1349 	retval = copy_io(clone_flags, p);
1350 	if (retval)
1351 		goto bad_fork_cleanup_namespaces;
1352 	retval = copy_thread(clone_flags, stack_start, stack_size, p);
1353 	if (retval)
1354 		goto bad_fork_cleanup_io;
1355 
1356 	if (pid != &init_struct_pid) {
1357 		retval = -ENOMEM;
1358 		pid = alloc_pid(p->nsproxy->pid_ns_for_children);
1359 		if (!pid)
1360 			goto bad_fork_cleanup_io;
1361 	}
1362 
1363 	p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1364 	/*
1365 	 * Clear TID on mm_release()?
1366 	 */
1367 	p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
1368 #ifdef CONFIG_BLOCK
1369 	p->plug = NULL;
1370 #endif
1371 #ifdef CONFIG_FUTEX
1372 	p->robust_list = NULL;
1373 #ifdef CONFIG_COMPAT
1374 	p->compat_robust_list = NULL;
1375 #endif
1376 	INIT_LIST_HEAD(&p->pi_state_list);
1377 	p->pi_state_cache = NULL;
1378 #endif
1379 	/*
1380 	 * sigaltstack should be cleared when sharing the same VM
1381 	 */
1382 	if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1383 		p->sas_ss_sp = p->sas_ss_size = 0;
1384 
1385 	/*
1386 	 * Syscall tracing and stepping should be turned off in the
1387 	 * child regardless of CLONE_PTRACE.
1388 	 */
1389 	user_disable_single_step(p);
1390 	clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1391 #ifdef TIF_SYSCALL_EMU
1392 	clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1393 #endif
1394 	clear_all_latency_tracing(p);
1395 
1396 	/* ok, now we should be set up.. */
1397 	p->pid = pid_nr(pid);
1398 	if (clone_flags & CLONE_THREAD) {
1399 		p->exit_signal = -1;
1400 		p->group_leader = current->group_leader;
1401 		p->tgid = current->tgid;
1402 	} else {
1403 		if (clone_flags & CLONE_PARENT)
1404 			p->exit_signal = current->group_leader->exit_signal;
1405 		else
1406 			p->exit_signal = (clone_flags & CSIGNAL);
1407 		p->group_leader = p;
1408 		p->tgid = p->pid;
1409 	}
1410 
1411 	p->nr_dirtied = 0;
1412 	p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
1413 	p->dirty_paused_when = 0;
1414 
1415 	p->pdeath_signal = 0;
1416 	INIT_LIST_HEAD(&p->thread_group);
1417 	p->task_works = NULL;
1418 
1419 	/*
1420 	 * Make it visible to the rest of the system, but dont wake it up yet.
1421 	 * Need tasklist lock for parent etc handling!
1422 	 */
1423 	write_lock_irq(&tasklist_lock);
1424 
1425 	/* CLONE_PARENT re-uses the old parent */
1426 	if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1427 		p->real_parent = current->real_parent;
1428 		p->parent_exec_id = current->parent_exec_id;
1429 	} else {
1430 		p->real_parent = current;
1431 		p->parent_exec_id = current->self_exec_id;
1432 	}
1433 
1434 	spin_lock(&current->sighand->siglock);
1435 
1436 	/*
1437 	 * Process group and session signals need to be delivered to just the
1438 	 * parent before the fork or both the parent and the child after the
1439 	 * fork. Restart if a signal comes in before we add the new process to
1440 	 * it's process group.
1441 	 * A fatal signal pending means that current will exit, so the new
1442 	 * thread can't slip out of an OOM kill (or normal SIGKILL).
1443 	*/
1444 	recalc_sigpending();
1445 	if (signal_pending(current)) {
1446 		spin_unlock(&current->sighand->siglock);
1447 		write_unlock_irq(&tasklist_lock);
1448 		retval = -ERESTARTNOINTR;
1449 		goto bad_fork_free_pid;
1450 	}
1451 
1452 	if (likely(p->pid)) {
1453 		ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
1454 
1455 		init_task_pid(p, PIDTYPE_PID, pid);
1456 		if (thread_group_leader(p)) {
1457 			init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
1458 			init_task_pid(p, PIDTYPE_SID, task_session(current));
1459 
1460 			if (is_child_reaper(pid)) {
1461 				ns_of_pid(pid)->child_reaper = p;
1462 				p->signal->flags |= SIGNAL_UNKILLABLE;
1463 			}
1464 
1465 			p->signal->leader_pid = pid;
1466 			p->signal->tty = tty_kref_get(current->signal->tty);
1467 			list_add_tail(&p->sibling, &p->real_parent->children);
1468 			list_add_tail_rcu(&p->tasks, &init_task.tasks);
1469 			attach_pid(p, PIDTYPE_PGID);
1470 			attach_pid(p, PIDTYPE_SID);
1471 			__this_cpu_inc(process_counts);
1472 		} else {
1473 			current->signal->nr_threads++;
1474 			atomic_inc(&current->signal->live);
1475 			atomic_inc(&current->signal->sigcnt);
1476 			list_add_tail_rcu(&p->thread_group,
1477 					  &p->group_leader->thread_group);
1478 			list_add_tail_rcu(&p->thread_node,
1479 					  &p->signal->thread_head);
1480 		}
1481 		attach_pid(p, PIDTYPE_PID);
1482 		nr_threads++;
1483 	}
1484 
1485 	total_forks++;
1486 	spin_unlock(&current->sighand->siglock);
1487 	write_unlock_irq(&tasklist_lock);
1488 	proc_fork_connector(p);
1489 	cgroup_post_fork(p);
1490 	if (clone_flags & CLONE_THREAD)
1491 		threadgroup_change_end(current);
1492 	perf_event_fork(p);
1493 
1494 	trace_task_newtask(p, clone_flags);
1495 	uprobe_copy_process(p, clone_flags);
1496 
1497 	return p;
1498 
1499 bad_fork_free_pid:
1500 	if (pid != &init_struct_pid)
1501 		free_pid(pid);
1502 bad_fork_cleanup_io:
1503 	if (p->io_context)
1504 		exit_io_context(p);
1505 bad_fork_cleanup_namespaces:
1506 	exit_task_namespaces(p);
1507 bad_fork_cleanup_mm:
1508 	if (p->mm)
1509 		mmput(p->mm);
1510 bad_fork_cleanup_signal:
1511 	if (!(clone_flags & CLONE_THREAD))
1512 		free_signal_struct(p->signal);
1513 bad_fork_cleanup_sighand:
1514 	__cleanup_sighand(p->sighand);
1515 bad_fork_cleanup_fs:
1516 	exit_fs(p); /* blocking */
1517 bad_fork_cleanup_files:
1518 	exit_files(p); /* blocking */
1519 bad_fork_cleanup_semundo:
1520 	exit_sem(p);
1521 bad_fork_cleanup_audit:
1522 	audit_free(p);
1523 bad_fork_cleanup_policy:
1524 	perf_event_free_task(p);
1525 #ifdef CONFIG_NUMA
1526 	mpol_put(p->mempolicy);
1527 bad_fork_cleanup_cgroup:
1528 #endif
1529 	if (clone_flags & CLONE_THREAD)
1530 		threadgroup_change_end(current);
1531 	cgroup_exit(p, 0);
1532 	delayacct_tsk_free(p);
1533 	module_put(task_thread_info(p)->exec_domain->module);
1534 bad_fork_cleanup_count:
1535 	atomic_dec(&p->cred->user->processes);
1536 	exit_creds(p);
1537 bad_fork_free:
1538 	free_task(p);
1539 fork_out:
1540 	return ERR_PTR(retval);
1541 }
1542 
1543 static inline void init_idle_pids(struct pid_link *links)
1544 {
1545 	enum pid_type type;
1546 
1547 	for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1548 		INIT_HLIST_NODE(&links[type].node); /* not really needed */
1549 		links[type].pid = &init_struct_pid;
1550 	}
1551 }
1552 
1553 struct task_struct *fork_idle(int cpu)
1554 {
1555 	struct task_struct *task;
1556 	task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0);
1557 	if (!IS_ERR(task)) {
1558 		init_idle_pids(task->pids);
1559 		init_idle(task, cpu);
1560 	}
1561 
1562 	return task;
1563 }
1564 
1565 /*
1566  *  Ok, this is the main fork-routine.
1567  *
1568  * It copies the process, and if successful kick-starts
1569  * it and waits for it to finish using the VM if required.
1570  */
1571 long do_fork(unsigned long clone_flags,
1572 	      unsigned long stack_start,
1573 	      unsigned long stack_size,
1574 	      int __user *parent_tidptr,
1575 	      int __user *child_tidptr)
1576 {
1577 	struct task_struct *p;
1578 	int trace = 0;
1579 	long nr;
1580 
1581 	/*
1582 	 * Determine whether and which event to report to ptracer.  When
1583 	 * called from kernel_thread or CLONE_UNTRACED is explicitly
1584 	 * requested, no event is reported; otherwise, report if the event
1585 	 * for the type of forking is enabled.
1586 	 */
1587 	if (!(clone_flags & CLONE_UNTRACED)) {
1588 		if (clone_flags & CLONE_VFORK)
1589 			trace = PTRACE_EVENT_VFORK;
1590 		else if ((clone_flags & CSIGNAL) != SIGCHLD)
1591 			trace = PTRACE_EVENT_CLONE;
1592 		else
1593 			trace = PTRACE_EVENT_FORK;
1594 
1595 		if (likely(!ptrace_event_enabled(current, trace)))
1596 			trace = 0;
1597 	}
1598 
1599 	p = copy_process(clone_flags, stack_start, stack_size,
1600 			 child_tidptr, NULL, trace);
1601 	/*
1602 	 * Do this prior waking up the new thread - the thread pointer
1603 	 * might get invalid after that point, if the thread exits quickly.
1604 	 */
1605 	if (!IS_ERR(p)) {
1606 		struct completion vfork;
1607 
1608 		trace_sched_process_fork(current, p);
1609 
1610 		nr = task_pid_vnr(p);
1611 
1612 		if (clone_flags & CLONE_PARENT_SETTID)
1613 			put_user(nr, parent_tidptr);
1614 
1615 		if (clone_flags & CLONE_VFORK) {
1616 			p->vfork_done = &vfork;
1617 			init_completion(&vfork);
1618 			get_task_struct(p);
1619 		}
1620 
1621 		wake_up_new_task(p);
1622 
1623 		/* forking complete and child started to run, tell ptracer */
1624 		if (unlikely(trace))
1625 			ptrace_event(trace, nr);
1626 
1627 		if (clone_flags & CLONE_VFORK) {
1628 			if (!wait_for_vfork_done(p, &vfork))
1629 				ptrace_event(PTRACE_EVENT_VFORK_DONE, nr);
1630 		}
1631 	} else {
1632 		nr = PTR_ERR(p);
1633 	}
1634 	return nr;
1635 }
1636 
1637 /*
1638  * Create a kernel thread.
1639  */
1640 pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
1641 {
1642 	return do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
1643 		(unsigned long)arg, NULL, NULL);
1644 }
1645 
1646 #ifdef __ARCH_WANT_SYS_FORK
1647 SYSCALL_DEFINE0(fork)
1648 {
1649 #ifdef CONFIG_MMU
1650 	return do_fork(SIGCHLD, 0, 0, NULL, NULL);
1651 #else
1652 	/* can not support in nommu mode */
1653 	return -EINVAL;
1654 #endif
1655 }
1656 #endif
1657 
1658 #ifdef __ARCH_WANT_SYS_VFORK
1659 SYSCALL_DEFINE0(vfork)
1660 {
1661 	return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0,
1662 			0, NULL, NULL);
1663 }
1664 #endif
1665 
1666 #ifdef __ARCH_WANT_SYS_CLONE
1667 #ifdef CONFIG_CLONE_BACKWARDS
1668 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1669 		 int __user *, parent_tidptr,
1670 		 int, tls_val,
1671 		 int __user *, child_tidptr)
1672 #elif defined(CONFIG_CLONE_BACKWARDS2)
1673 SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
1674 		 int __user *, parent_tidptr,
1675 		 int __user *, child_tidptr,
1676 		 int, tls_val)
1677 #elif defined(CONFIG_CLONE_BACKWARDS3)
1678 SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
1679 		int, stack_size,
1680 		int __user *, parent_tidptr,
1681 		int __user *, child_tidptr,
1682 		int, tls_val)
1683 #else
1684 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1685 		 int __user *, parent_tidptr,
1686 		 int __user *, child_tidptr,
1687 		 int, tls_val)
1688 #endif
1689 {
1690 	return do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr);
1691 }
1692 #endif
1693 
1694 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1695 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1696 #endif
1697 
1698 static void sighand_ctor(void *data)
1699 {
1700 	struct sighand_struct *sighand = data;
1701 
1702 	spin_lock_init(&sighand->siglock);
1703 	init_waitqueue_head(&sighand->signalfd_wqh);
1704 }
1705 
1706 void __init proc_caches_init(void)
1707 {
1708 	sighand_cachep = kmem_cache_create("sighand_cache",
1709 			sizeof(struct sighand_struct), 0,
1710 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1711 			SLAB_NOTRACK, sighand_ctor);
1712 	signal_cachep = kmem_cache_create("signal_cache",
1713 			sizeof(struct signal_struct), 0,
1714 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1715 	files_cachep = kmem_cache_create("files_cache",
1716 			sizeof(struct files_struct), 0,
1717 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1718 	fs_cachep = kmem_cache_create("fs_cache",
1719 			sizeof(struct fs_struct), 0,
1720 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1721 	/*
1722 	 * FIXME! The "sizeof(struct mm_struct)" currently includes the
1723 	 * whole struct cpumask for the OFFSTACK case. We could change
1724 	 * this to *only* allocate as much of it as required by the
1725 	 * maximum number of CPU's we can ever have.  The cpumask_allocation
1726 	 * is at the end of the structure, exactly for that reason.
1727 	 */
1728 	mm_cachep = kmem_cache_create("mm_struct",
1729 			sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1730 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1731 	vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1732 	mmap_init();
1733 	nsproxy_cache_init();
1734 }
1735 
1736 /*
1737  * Check constraints on flags passed to the unshare system call.
1738  */
1739 static int check_unshare_flags(unsigned long unshare_flags)
1740 {
1741 	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1742 				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1743 				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
1744 				CLONE_NEWUSER|CLONE_NEWPID))
1745 		return -EINVAL;
1746 	/*
1747 	 * Not implemented, but pretend it works if there is nothing to
1748 	 * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
1749 	 * needs to unshare vm.
1750 	 */
1751 	if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
1752 		/* FIXME: get_task_mm() increments ->mm_users */
1753 		if (atomic_read(&current->mm->mm_users) > 1)
1754 			return -EINVAL;
1755 	}
1756 
1757 	return 0;
1758 }
1759 
1760 /*
1761  * Unshare the filesystem structure if it is being shared
1762  */
1763 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1764 {
1765 	struct fs_struct *fs = current->fs;
1766 
1767 	if (!(unshare_flags & CLONE_FS) || !fs)
1768 		return 0;
1769 
1770 	/* don't need lock here; in the worst case we'll do useless copy */
1771 	if (fs->users == 1)
1772 		return 0;
1773 
1774 	*new_fsp = copy_fs_struct(fs);
1775 	if (!*new_fsp)
1776 		return -ENOMEM;
1777 
1778 	return 0;
1779 }
1780 
1781 /*
1782  * Unshare file descriptor table if it is being shared
1783  */
1784 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1785 {
1786 	struct files_struct *fd = current->files;
1787 	int error = 0;
1788 
1789 	if ((unshare_flags & CLONE_FILES) &&
1790 	    (fd && atomic_read(&fd->count) > 1)) {
1791 		*new_fdp = dup_fd(fd, &error);
1792 		if (!*new_fdp)
1793 			return error;
1794 	}
1795 
1796 	return 0;
1797 }
1798 
1799 /*
1800  * unshare allows a process to 'unshare' part of the process
1801  * context which was originally shared using clone.  copy_*
1802  * functions used by do_fork() cannot be used here directly
1803  * because they modify an inactive task_struct that is being
1804  * constructed. Here we are modifying the current, active,
1805  * task_struct.
1806  */
1807 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1808 {
1809 	struct fs_struct *fs, *new_fs = NULL;
1810 	struct files_struct *fd, *new_fd = NULL;
1811 	struct cred *new_cred = NULL;
1812 	struct nsproxy *new_nsproxy = NULL;
1813 	int do_sysvsem = 0;
1814 	int err;
1815 
1816 	/*
1817 	 * If unsharing a user namespace must also unshare the thread.
1818 	 */
1819 	if (unshare_flags & CLONE_NEWUSER)
1820 		unshare_flags |= CLONE_THREAD | CLONE_FS;
1821 	/*
1822 	 * If unsharing a thread from a thread group, must also unshare vm.
1823 	 */
1824 	if (unshare_flags & CLONE_THREAD)
1825 		unshare_flags |= CLONE_VM;
1826 	/*
1827 	 * If unsharing vm, must also unshare signal handlers.
1828 	 */
1829 	if (unshare_flags & CLONE_VM)
1830 		unshare_flags |= CLONE_SIGHAND;
1831 	/*
1832 	 * If unsharing namespace, must also unshare filesystem information.
1833 	 */
1834 	if (unshare_flags & CLONE_NEWNS)
1835 		unshare_flags |= CLONE_FS;
1836 
1837 	err = check_unshare_flags(unshare_flags);
1838 	if (err)
1839 		goto bad_unshare_out;
1840 	/*
1841 	 * CLONE_NEWIPC must also detach from the undolist: after switching
1842 	 * to a new ipc namespace, the semaphore arrays from the old
1843 	 * namespace are unreachable.
1844 	 */
1845 	if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1846 		do_sysvsem = 1;
1847 	err = unshare_fs(unshare_flags, &new_fs);
1848 	if (err)
1849 		goto bad_unshare_out;
1850 	err = unshare_fd(unshare_flags, &new_fd);
1851 	if (err)
1852 		goto bad_unshare_cleanup_fs;
1853 	err = unshare_userns(unshare_flags, &new_cred);
1854 	if (err)
1855 		goto bad_unshare_cleanup_fd;
1856 	err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
1857 					 new_cred, new_fs);
1858 	if (err)
1859 		goto bad_unshare_cleanup_cred;
1860 
1861 	if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
1862 		if (do_sysvsem) {
1863 			/*
1864 			 * CLONE_SYSVSEM is equivalent to sys_exit().
1865 			 */
1866 			exit_sem(current);
1867 		}
1868 
1869 		if (new_nsproxy)
1870 			switch_task_namespaces(current, new_nsproxy);
1871 
1872 		task_lock(current);
1873 
1874 		if (new_fs) {
1875 			fs = current->fs;
1876 			spin_lock(&fs->lock);
1877 			current->fs = new_fs;
1878 			if (--fs->users)
1879 				new_fs = NULL;
1880 			else
1881 				new_fs = fs;
1882 			spin_unlock(&fs->lock);
1883 		}
1884 
1885 		if (new_fd) {
1886 			fd = current->files;
1887 			current->files = new_fd;
1888 			new_fd = fd;
1889 		}
1890 
1891 		task_unlock(current);
1892 
1893 		if (new_cred) {
1894 			/* Install the new user namespace */
1895 			commit_creds(new_cred);
1896 			new_cred = NULL;
1897 		}
1898 	}
1899 
1900 bad_unshare_cleanup_cred:
1901 	if (new_cred)
1902 		put_cred(new_cred);
1903 bad_unshare_cleanup_fd:
1904 	if (new_fd)
1905 		put_files_struct(new_fd);
1906 
1907 bad_unshare_cleanup_fs:
1908 	if (new_fs)
1909 		free_fs_struct(new_fs);
1910 
1911 bad_unshare_out:
1912 	return err;
1913 }
1914 
1915 /*
1916  *	Helper to unshare the files of the current task.
1917  *	We don't want to expose copy_files internals to
1918  *	the exec layer of the kernel.
1919  */
1920 
1921 int unshare_files(struct files_struct **displaced)
1922 {
1923 	struct task_struct *task = current;
1924 	struct files_struct *copy = NULL;
1925 	int error;
1926 
1927 	error = unshare_fd(CLONE_FILES, &copy);
1928 	if (error || !copy) {
1929 		*displaced = NULL;
1930 		return error;
1931 	}
1932 	*displaced = task->files;
1933 	task_lock(task);
1934 	task->files = copy;
1935 	task_unlock(task);
1936 	return 0;
1937 }
1938