xref: /openbmc/linux/kernel/fork.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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/mnt_namespace.h>
21 #include <linux/personality.h>
22 #include <linux/mempolicy.h>
23 #include <linux/sem.h>
24 #include <linux/file.h>
25 #include <linux/key.h>
26 #include <linux/binfmts.h>
27 #include <linux/mman.h>
28 #include <linux/fs.h>
29 #include <linux/nsproxy.h>
30 #include <linux/capability.h>
31 #include <linux/cpu.h>
32 #include <linux/cpuset.h>
33 #include <linux/security.h>
34 #include <linux/swap.h>
35 #include <linux/syscalls.h>
36 #include <linux/jiffies.h>
37 #include <linux/futex.h>
38 #include <linux/task_io_accounting_ops.h>
39 #include <linux/rcupdate.h>
40 #include <linux/ptrace.h>
41 #include <linux/mount.h>
42 #include <linux/audit.h>
43 #include <linux/profile.h>
44 #include <linux/rmap.h>
45 #include <linux/acct.h>
46 #include <linux/tsacct_kern.h>
47 #include <linux/cn_proc.h>
48 #include <linux/delayacct.h>
49 #include <linux/taskstats_kern.h>
50 #include <linux/random.h>
51 
52 #include <asm/pgtable.h>
53 #include <asm/pgalloc.h>
54 #include <asm/uaccess.h>
55 #include <asm/mmu_context.h>
56 #include <asm/cacheflush.h>
57 #include <asm/tlbflush.h>
58 
59 /*
60  * Protected counters by write_lock_irq(&tasklist_lock)
61  */
62 unsigned long total_forks;	/* Handle normal Linux uptimes. */
63 int nr_threads; 		/* The idle threads do not count.. */
64 
65 int max_threads;		/* tunable limit on nr_threads */
66 
67 DEFINE_PER_CPU(unsigned long, process_counts) = 0;
68 
69 __cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
70 
71 int nr_processes(void)
72 {
73 	int cpu;
74 	int total = 0;
75 
76 	for_each_online_cpu(cpu)
77 		total += per_cpu(process_counts, cpu);
78 
79 	return total;
80 }
81 
82 #ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
83 # define alloc_task_struct()	kmem_cache_alloc(task_struct_cachep, GFP_KERNEL)
84 # define free_task_struct(tsk)	kmem_cache_free(task_struct_cachep, (tsk))
85 static struct kmem_cache *task_struct_cachep;
86 #endif
87 
88 /* SLAB cache for signal_struct structures (tsk->signal) */
89 static struct kmem_cache *signal_cachep;
90 
91 /* SLAB cache for sighand_struct structures (tsk->sighand) */
92 struct kmem_cache *sighand_cachep;
93 
94 /* SLAB cache for files_struct structures (tsk->files) */
95 struct kmem_cache *files_cachep;
96 
97 /* SLAB cache for fs_struct structures (tsk->fs) */
98 struct kmem_cache *fs_cachep;
99 
100 /* SLAB cache for vm_area_struct structures */
101 struct kmem_cache *vm_area_cachep;
102 
103 /* SLAB cache for mm_struct structures (tsk->mm) */
104 static struct kmem_cache *mm_cachep;
105 
106 void free_task(struct task_struct *tsk)
107 {
108 	free_thread_info(tsk->stack);
109 	rt_mutex_debug_task_free(tsk);
110 	free_task_struct(tsk);
111 }
112 EXPORT_SYMBOL(free_task);
113 
114 void __put_task_struct(struct task_struct *tsk)
115 {
116 	WARN_ON(!(tsk->exit_state & (EXIT_DEAD | EXIT_ZOMBIE)));
117 	WARN_ON(atomic_read(&tsk->usage));
118 	WARN_ON(tsk == current);
119 
120 	security_task_free(tsk);
121 	free_uid(tsk->user);
122 	put_group_info(tsk->group_info);
123 	delayacct_tsk_free(tsk);
124 
125 	if (!profile_handoff_task(tsk))
126 		free_task(tsk);
127 }
128 
129 void __init fork_init(unsigned long mempages)
130 {
131 #ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
132 #ifndef ARCH_MIN_TASKALIGN
133 #define ARCH_MIN_TASKALIGN	L1_CACHE_BYTES
134 #endif
135 	/* create a slab on which task_structs can be allocated */
136 	task_struct_cachep =
137 		kmem_cache_create("task_struct", sizeof(struct task_struct),
138 			ARCH_MIN_TASKALIGN, SLAB_PANIC, NULL, NULL);
139 #endif
140 
141 	/*
142 	 * The default maximum number of threads is set to a safe
143 	 * value: the thread structures can take up at most half
144 	 * of memory.
145 	 */
146 	max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
147 
148 	/*
149 	 * we need to allow at least 20 threads to boot a system
150 	 */
151 	if(max_threads < 20)
152 		max_threads = 20;
153 
154 	init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
155 	init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
156 	init_task.signal->rlim[RLIMIT_SIGPENDING] =
157 		init_task.signal->rlim[RLIMIT_NPROC];
158 }
159 
160 static struct task_struct *dup_task_struct(struct task_struct *orig)
161 {
162 	struct task_struct *tsk;
163 	struct thread_info *ti;
164 
165 	prepare_to_copy(orig);
166 
167 	tsk = alloc_task_struct();
168 	if (!tsk)
169 		return NULL;
170 
171 	ti = alloc_thread_info(tsk);
172 	if (!ti) {
173 		free_task_struct(tsk);
174 		return NULL;
175 	}
176 
177 	*tsk = *orig;
178 	tsk->stack = ti;
179 	setup_thread_stack(tsk, orig);
180 
181 #ifdef CONFIG_CC_STACKPROTECTOR
182 	tsk->stack_canary = get_random_int();
183 #endif
184 
185 	/* One for us, one for whoever does the "release_task()" (usually parent) */
186 	atomic_set(&tsk->usage,2);
187 	atomic_set(&tsk->fs_excl, 0);
188 #ifdef CONFIG_BLK_DEV_IO_TRACE
189 	tsk->btrace_seq = 0;
190 #endif
191 	tsk->splice_pipe = NULL;
192 	return tsk;
193 }
194 
195 #ifdef CONFIG_MMU
196 static inline int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
197 {
198 	struct vm_area_struct *mpnt, *tmp, **pprev;
199 	struct rb_node **rb_link, *rb_parent;
200 	int retval;
201 	unsigned long charge;
202 	struct mempolicy *pol;
203 
204 	down_write(&oldmm->mmap_sem);
205 	flush_cache_dup_mm(oldmm);
206 	/*
207 	 * Not linked in yet - no deadlock potential:
208 	 */
209 	down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
210 
211 	mm->locked_vm = 0;
212 	mm->mmap = NULL;
213 	mm->mmap_cache = NULL;
214 	mm->free_area_cache = oldmm->mmap_base;
215 	mm->cached_hole_size = ~0UL;
216 	mm->map_count = 0;
217 	cpus_clear(mm->cpu_vm_mask);
218 	mm->mm_rb = RB_ROOT;
219 	rb_link = &mm->mm_rb.rb_node;
220 	rb_parent = NULL;
221 	pprev = &mm->mmap;
222 
223 	for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
224 		struct file *file;
225 
226 		if (mpnt->vm_flags & VM_DONTCOPY) {
227 			long pages = vma_pages(mpnt);
228 			mm->total_vm -= pages;
229 			vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
230 								-pages);
231 			continue;
232 		}
233 		charge = 0;
234 		if (mpnt->vm_flags & VM_ACCOUNT) {
235 			unsigned int len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
236 			if (security_vm_enough_memory(len))
237 				goto fail_nomem;
238 			charge = len;
239 		}
240 		tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
241 		if (!tmp)
242 			goto fail_nomem;
243 		*tmp = *mpnt;
244 		pol = mpol_copy(vma_policy(mpnt));
245 		retval = PTR_ERR(pol);
246 		if (IS_ERR(pol))
247 			goto fail_nomem_policy;
248 		vma_set_policy(tmp, pol);
249 		tmp->vm_flags &= ~VM_LOCKED;
250 		tmp->vm_mm = mm;
251 		tmp->vm_next = NULL;
252 		anon_vma_link(tmp);
253 		file = tmp->vm_file;
254 		if (file) {
255 			struct inode *inode = file->f_path.dentry->d_inode;
256 			get_file(file);
257 			if (tmp->vm_flags & VM_DENYWRITE)
258 				atomic_dec(&inode->i_writecount);
259 
260 			/* insert tmp into the share list, just after mpnt */
261 			spin_lock(&file->f_mapping->i_mmap_lock);
262 			tmp->vm_truncate_count = mpnt->vm_truncate_count;
263 			flush_dcache_mmap_lock(file->f_mapping);
264 			vma_prio_tree_add(tmp, mpnt);
265 			flush_dcache_mmap_unlock(file->f_mapping);
266 			spin_unlock(&file->f_mapping->i_mmap_lock);
267 		}
268 
269 		/*
270 		 * Link in the new vma and copy the page table entries.
271 		 */
272 		*pprev = tmp;
273 		pprev = &tmp->vm_next;
274 
275 		__vma_link_rb(mm, tmp, rb_link, rb_parent);
276 		rb_link = &tmp->vm_rb.rb_right;
277 		rb_parent = &tmp->vm_rb;
278 
279 		mm->map_count++;
280 		retval = copy_page_range(mm, oldmm, mpnt);
281 
282 		if (tmp->vm_ops && tmp->vm_ops->open)
283 			tmp->vm_ops->open(tmp);
284 
285 		if (retval)
286 			goto out;
287 	}
288 	/* a new mm has just been created */
289 	arch_dup_mmap(oldmm, mm);
290 	retval = 0;
291 out:
292 	up_write(&mm->mmap_sem);
293 	flush_tlb_mm(oldmm);
294 	up_write(&oldmm->mmap_sem);
295 	return retval;
296 fail_nomem_policy:
297 	kmem_cache_free(vm_area_cachep, tmp);
298 fail_nomem:
299 	retval = -ENOMEM;
300 	vm_unacct_memory(charge);
301 	goto out;
302 }
303 
304 static inline int mm_alloc_pgd(struct mm_struct * mm)
305 {
306 	mm->pgd = pgd_alloc(mm);
307 	if (unlikely(!mm->pgd))
308 		return -ENOMEM;
309 	return 0;
310 }
311 
312 static inline void mm_free_pgd(struct mm_struct * mm)
313 {
314 	pgd_free(mm->pgd);
315 }
316 #else
317 #define dup_mmap(mm, oldmm)	(0)
318 #define mm_alloc_pgd(mm)	(0)
319 #define mm_free_pgd(mm)
320 #endif /* CONFIG_MMU */
321 
322  __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
323 
324 #define allocate_mm()	(kmem_cache_alloc(mm_cachep, GFP_KERNEL))
325 #define free_mm(mm)	(kmem_cache_free(mm_cachep, (mm)))
326 
327 #include <linux/init_task.h>
328 
329 static struct mm_struct * mm_init(struct mm_struct * mm)
330 {
331 	atomic_set(&mm->mm_users, 1);
332 	atomic_set(&mm->mm_count, 1);
333 	init_rwsem(&mm->mmap_sem);
334 	INIT_LIST_HEAD(&mm->mmlist);
335 	mm->core_waiters = 0;
336 	mm->nr_ptes = 0;
337 	set_mm_counter(mm, file_rss, 0);
338 	set_mm_counter(mm, anon_rss, 0);
339 	spin_lock_init(&mm->page_table_lock);
340 	rwlock_init(&mm->ioctx_list_lock);
341 	mm->ioctx_list = NULL;
342 	mm->free_area_cache = TASK_UNMAPPED_BASE;
343 	mm->cached_hole_size = ~0UL;
344 
345 	if (likely(!mm_alloc_pgd(mm))) {
346 		mm->def_flags = 0;
347 		return mm;
348 	}
349 	free_mm(mm);
350 	return NULL;
351 }
352 
353 /*
354  * Allocate and initialize an mm_struct.
355  */
356 struct mm_struct * mm_alloc(void)
357 {
358 	struct mm_struct * mm;
359 
360 	mm = allocate_mm();
361 	if (mm) {
362 		memset(mm, 0, sizeof(*mm));
363 		mm = mm_init(mm);
364 	}
365 	return mm;
366 }
367 
368 /*
369  * Called when the last reference to the mm
370  * is dropped: either by a lazy thread or by
371  * mmput. Free the page directory and the mm.
372  */
373 void fastcall __mmdrop(struct mm_struct *mm)
374 {
375 	BUG_ON(mm == &init_mm);
376 	mm_free_pgd(mm);
377 	destroy_context(mm);
378 	free_mm(mm);
379 }
380 
381 /*
382  * Decrement the use count and release all resources for an mm.
383  */
384 void mmput(struct mm_struct *mm)
385 {
386 	might_sleep();
387 
388 	if (atomic_dec_and_test(&mm->mm_users)) {
389 		exit_aio(mm);
390 		exit_mmap(mm);
391 		if (!list_empty(&mm->mmlist)) {
392 			spin_lock(&mmlist_lock);
393 			list_del(&mm->mmlist);
394 			spin_unlock(&mmlist_lock);
395 		}
396 		put_swap_token(mm);
397 		mmdrop(mm);
398 	}
399 }
400 EXPORT_SYMBOL_GPL(mmput);
401 
402 /**
403  * get_task_mm - acquire a reference to the task's mm
404  *
405  * Returns %NULL if the task has no mm.  Checks PF_BORROWED_MM (meaning
406  * this kernel workthread has transiently adopted a user mm with use_mm,
407  * to do its AIO) is not set and if so returns a reference to it, after
408  * bumping up the use count.  User must release the mm via mmput()
409  * after use.  Typically used by /proc and ptrace.
410  */
411 struct mm_struct *get_task_mm(struct task_struct *task)
412 {
413 	struct mm_struct *mm;
414 
415 	task_lock(task);
416 	mm = task->mm;
417 	if (mm) {
418 		if (task->flags & PF_BORROWED_MM)
419 			mm = NULL;
420 		else
421 			atomic_inc(&mm->mm_users);
422 	}
423 	task_unlock(task);
424 	return mm;
425 }
426 EXPORT_SYMBOL_GPL(get_task_mm);
427 
428 /* Please note the differences between mmput and mm_release.
429  * mmput is called whenever we stop holding onto a mm_struct,
430  * error success whatever.
431  *
432  * mm_release is called after a mm_struct has been removed
433  * from the current process.
434  *
435  * This difference is important for error handling, when we
436  * only half set up a mm_struct for a new process and need to restore
437  * the old one.  Because we mmput the new mm_struct before
438  * restoring the old one. . .
439  * Eric Biederman 10 January 1998
440  */
441 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
442 {
443 	struct completion *vfork_done = tsk->vfork_done;
444 
445 	/* Get rid of any cached register state */
446 	deactivate_mm(tsk, mm);
447 
448 	/* notify parent sleeping on vfork() */
449 	if (vfork_done) {
450 		tsk->vfork_done = NULL;
451 		complete(vfork_done);
452 	}
453 
454 	/*
455 	 * If we're exiting normally, clear a user-space tid field if
456 	 * requested.  We leave this alone when dying by signal, to leave
457 	 * the value intact in a core dump, and to save the unnecessary
458 	 * trouble otherwise.  Userland only wants this done for a sys_exit.
459 	 */
460 	if (tsk->clear_child_tid
461 	    && !(tsk->flags & PF_SIGNALED)
462 	    && atomic_read(&mm->mm_users) > 1) {
463 		u32 __user * tidptr = tsk->clear_child_tid;
464 		tsk->clear_child_tid = NULL;
465 
466 		/*
467 		 * We don't check the error code - if userspace has
468 		 * not set up a proper pointer then tough luck.
469 		 */
470 		put_user(0, tidptr);
471 		sys_futex(tidptr, FUTEX_WAKE, 1, NULL, NULL, 0);
472 	}
473 }
474 
475 /*
476  * Allocate a new mm structure and copy contents from the
477  * mm structure of the passed in task structure.
478  */
479 static struct mm_struct *dup_mm(struct task_struct *tsk)
480 {
481 	struct mm_struct *mm, *oldmm = current->mm;
482 	int err;
483 
484 	if (!oldmm)
485 		return NULL;
486 
487 	mm = allocate_mm();
488 	if (!mm)
489 		goto fail_nomem;
490 
491 	memcpy(mm, oldmm, sizeof(*mm));
492 
493 	/* Initializing for Swap token stuff */
494 	mm->token_priority = 0;
495 	mm->last_interval = 0;
496 
497 	if (!mm_init(mm))
498 		goto fail_nomem;
499 
500 	if (init_new_context(tsk, mm))
501 		goto fail_nocontext;
502 
503 	err = dup_mmap(mm, oldmm);
504 	if (err)
505 		goto free_pt;
506 
507 	mm->hiwater_rss = get_mm_rss(mm);
508 	mm->hiwater_vm = mm->total_vm;
509 
510 	return mm;
511 
512 free_pt:
513 	mmput(mm);
514 
515 fail_nomem:
516 	return NULL;
517 
518 fail_nocontext:
519 	/*
520 	 * If init_new_context() failed, we cannot use mmput() to free the mm
521 	 * because it calls destroy_context()
522 	 */
523 	mm_free_pgd(mm);
524 	free_mm(mm);
525 	return NULL;
526 }
527 
528 static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
529 {
530 	struct mm_struct * mm, *oldmm;
531 	int retval;
532 
533 	tsk->min_flt = tsk->maj_flt = 0;
534 	tsk->nvcsw = tsk->nivcsw = 0;
535 
536 	tsk->mm = NULL;
537 	tsk->active_mm = NULL;
538 
539 	/*
540 	 * Are we cloning a kernel thread?
541 	 *
542 	 * We need to steal a active VM for that..
543 	 */
544 	oldmm = current->mm;
545 	if (!oldmm)
546 		return 0;
547 
548 	if (clone_flags & CLONE_VM) {
549 		atomic_inc(&oldmm->mm_users);
550 		mm = oldmm;
551 		goto good_mm;
552 	}
553 
554 	retval = -ENOMEM;
555 	mm = dup_mm(tsk);
556 	if (!mm)
557 		goto fail_nomem;
558 
559 good_mm:
560 	/* Initializing for Swap token stuff */
561 	mm->token_priority = 0;
562 	mm->last_interval = 0;
563 
564 	tsk->mm = mm;
565 	tsk->active_mm = mm;
566 	return 0;
567 
568 fail_nomem:
569 	return retval;
570 }
571 
572 static inline struct fs_struct *__copy_fs_struct(struct fs_struct *old)
573 {
574 	struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
575 	/* We don't need to lock fs - think why ;-) */
576 	if (fs) {
577 		atomic_set(&fs->count, 1);
578 		rwlock_init(&fs->lock);
579 		fs->umask = old->umask;
580 		read_lock(&old->lock);
581 		fs->rootmnt = mntget(old->rootmnt);
582 		fs->root = dget(old->root);
583 		fs->pwdmnt = mntget(old->pwdmnt);
584 		fs->pwd = dget(old->pwd);
585 		if (old->altroot) {
586 			fs->altrootmnt = mntget(old->altrootmnt);
587 			fs->altroot = dget(old->altroot);
588 		} else {
589 			fs->altrootmnt = NULL;
590 			fs->altroot = NULL;
591 		}
592 		read_unlock(&old->lock);
593 	}
594 	return fs;
595 }
596 
597 struct fs_struct *copy_fs_struct(struct fs_struct *old)
598 {
599 	return __copy_fs_struct(old);
600 }
601 
602 EXPORT_SYMBOL_GPL(copy_fs_struct);
603 
604 static inline int copy_fs(unsigned long clone_flags, struct task_struct * tsk)
605 {
606 	if (clone_flags & CLONE_FS) {
607 		atomic_inc(&current->fs->count);
608 		return 0;
609 	}
610 	tsk->fs = __copy_fs_struct(current->fs);
611 	if (!tsk->fs)
612 		return -ENOMEM;
613 	return 0;
614 }
615 
616 static int count_open_files(struct fdtable *fdt)
617 {
618 	int size = fdt->max_fds;
619 	int i;
620 
621 	/* Find the last open fd */
622 	for (i = size/(8*sizeof(long)); i > 0; ) {
623 		if (fdt->open_fds->fds_bits[--i])
624 			break;
625 	}
626 	i = (i+1) * 8 * sizeof(long);
627 	return i;
628 }
629 
630 static struct files_struct *alloc_files(void)
631 {
632 	struct files_struct *newf;
633 	struct fdtable *fdt;
634 
635 	newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
636 	if (!newf)
637 		goto out;
638 
639 	atomic_set(&newf->count, 1);
640 
641 	spin_lock_init(&newf->file_lock);
642 	newf->next_fd = 0;
643 	fdt = &newf->fdtab;
644 	fdt->max_fds = NR_OPEN_DEFAULT;
645 	fdt->close_on_exec = (fd_set *)&newf->close_on_exec_init;
646 	fdt->open_fds = (fd_set *)&newf->open_fds_init;
647 	fdt->fd = &newf->fd_array[0];
648 	INIT_RCU_HEAD(&fdt->rcu);
649 	fdt->next = NULL;
650 	rcu_assign_pointer(newf->fdt, fdt);
651 out:
652 	return newf;
653 }
654 
655 /*
656  * Allocate a new files structure and copy contents from the
657  * passed in files structure.
658  * errorp will be valid only when the returned files_struct is NULL.
659  */
660 static struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
661 {
662 	struct files_struct *newf;
663 	struct file **old_fds, **new_fds;
664 	int open_files, size, i;
665 	struct fdtable *old_fdt, *new_fdt;
666 
667 	*errorp = -ENOMEM;
668 	newf = alloc_files();
669 	if (!newf)
670 		goto out;
671 
672 	spin_lock(&oldf->file_lock);
673 	old_fdt = files_fdtable(oldf);
674 	new_fdt = files_fdtable(newf);
675 	open_files = count_open_files(old_fdt);
676 
677 	/*
678 	 * Check whether we need to allocate a larger fd array and fd set.
679 	 * Note: we're not a clone task, so the open count won't change.
680 	 */
681 	if (open_files > new_fdt->max_fds) {
682 		new_fdt->max_fds = 0;
683 		spin_unlock(&oldf->file_lock);
684 		spin_lock(&newf->file_lock);
685 		*errorp = expand_files(newf, open_files-1);
686 		spin_unlock(&newf->file_lock);
687 		if (*errorp < 0)
688 			goto out_release;
689 		new_fdt = files_fdtable(newf);
690 		/*
691 		 * Reacquire the oldf lock and a pointer to its fd table
692 		 * who knows it may have a new bigger fd table. We need
693 		 * the latest pointer.
694 		 */
695 		spin_lock(&oldf->file_lock);
696 		old_fdt = files_fdtable(oldf);
697 	}
698 
699 	old_fds = old_fdt->fd;
700 	new_fds = new_fdt->fd;
701 
702 	memcpy(new_fdt->open_fds->fds_bits,
703 		old_fdt->open_fds->fds_bits, open_files/8);
704 	memcpy(new_fdt->close_on_exec->fds_bits,
705 		old_fdt->close_on_exec->fds_bits, open_files/8);
706 
707 	for (i = open_files; i != 0; i--) {
708 		struct file *f = *old_fds++;
709 		if (f) {
710 			get_file(f);
711 		} else {
712 			/*
713 			 * The fd may be claimed in the fd bitmap but not yet
714 			 * instantiated in the files array if a sibling thread
715 			 * is partway through open().  So make sure that this
716 			 * fd is available to the new process.
717 			 */
718 			FD_CLR(open_files - i, new_fdt->open_fds);
719 		}
720 		rcu_assign_pointer(*new_fds++, f);
721 	}
722 	spin_unlock(&oldf->file_lock);
723 
724 	/* compute the remainder to be cleared */
725 	size = (new_fdt->max_fds - open_files) * sizeof(struct file *);
726 
727 	/* This is long word aligned thus could use a optimized version */
728 	memset(new_fds, 0, size);
729 
730 	if (new_fdt->max_fds > open_files) {
731 		int left = (new_fdt->max_fds-open_files)/8;
732 		int start = open_files / (8 * sizeof(unsigned long));
733 
734 		memset(&new_fdt->open_fds->fds_bits[start], 0, left);
735 		memset(&new_fdt->close_on_exec->fds_bits[start], 0, left);
736 	}
737 
738 	return newf;
739 
740 out_release:
741 	kmem_cache_free(files_cachep, newf);
742 out:
743 	return NULL;
744 }
745 
746 static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
747 {
748 	struct files_struct *oldf, *newf;
749 	int error = 0;
750 
751 	/*
752 	 * A background process may not have any files ...
753 	 */
754 	oldf = current->files;
755 	if (!oldf)
756 		goto out;
757 
758 	if (clone_flags & CLONE_FILES) {
759 		atomic_inc(&oldf->count);
760 		goto out;
761 	}
762 
763 	/*
764 	 * Note: we may be using current for both targets (See exec.c)
765 	 * This works because we cache current->files (old) as oldf. Don't
766 	 * break this.
767 	 */
768 	tsk->files = NULL;
769 	newf = dup_fd(oldf, &error);
770 	if (!newf)
771 		goto out;
772 
773 	tsk->files = newf;
774 	error = 0;
775 out:
776 	return error;
777 }
778 
779 /*
780  *	Helper to unshare the files of the current task.
781  *	We don't want to expose copy_files internals to
782  *	the exec layer of the kernel.
783  */
784 
785 int unshare_files(void)
786 {
787 	struct files_struct *files  = current->files;
788 	int rc;
789 
790 	BUG_ON(!files);
791 
792 	/* This can race but the race causes us to copy when we don't
793 	   need to and drop the copy */
794 	if(atomic_read(&files->count) == 1)
795 	{
796 		atomic_inc(&files->count);
797 		return 0;
798 	}
799 	rc = copy_files(0, current);
800 	if(rc)
801 		current->files = files;
802 	return rc;
803 }
804 
805 EXPORT_SYMBOL(unshare_files);
806 
807 static inline int copy_sighand(unsigned long clone_flags, struct task_struct * tsk)
808 {
809 	struct sighand_struct *sig;
810 
811 	if (clone_flags & (CLONE_SIGHAND | CLONE_THREAD)) {
812 		atomic_inc(&current->sighand->count);
813 		return 0;
814 	}
815 	sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
816 	rcu_assign_pointer(tsk->sighand, sig);
817 	if (!sig)
818 		return -ENOMEM;
819 	atomic_set(&sig->count, 1);
820 	memcpy(sig->action, current->sighand->action, sizeof(sig->action));
821 	return 0;
822 }
823 
824 void __cleanup_sighand(struct sighand_struct *sighand)
825 {
826 	if (atomic_dec_and_test(&sighand->count))
827 		kmem_cache_free(sighand_cachep, sighand);
828 }
829 
830 static inline int copy_signal(unsigned long clone_flags, struct task_struct * tsk)
831 {
832 	struct signal_struct *sig;
833 	int ret;
834 
835 	if (clone_flags & CLONE_THREAD) {
836 		atomic_inc(&current->signal->count);
837 		atomic_inc(&current->signal->live);
838 		return 0;
839 	}
840 	sig = kmem_cache_alloc(signal_cachep, GFP_KERNEL);
841 	tsk->signal = sig;
842 	if (!sig)
843 		return -ENOMEM;
844 
845 	ret = copy_thread_group_keys(tsk);
846 	if (ret < 0) {
847 		kmem_cache_free(signal_cachep, sig);
848 		return ret;
849 	}
850 
851 	atomic_set(&sig->count, 1);
852 	atomic_set(&sig->live, 1);
853 	init_waitqueue_head(&sig->wait_chldexit);
854 	sig->flags = 0;
855 	sig->group_exit_code = 0;
856 	sig->group_exit_task = NULL;
857 	sig->group_stop_count = 0;
858 	sig->curr_target = NULL;
859 	init_sigpending(&sig->shared_pending);
860 	INIT_LIST_HEAD(&sig->posix_timers);
861 
862 	hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
863 	sig->it_real_incr.tv64 = 0;
864 	sig->real_timer.function = it_real_fn;
865 	sig->tsk = tsk;
866 
867 	sig->it_virt_expires = cputime_zero;
868 	sig->it_virt_incr = cputime_zero;
869 	sig->it_prof_expires = cputime_zero;
870 	sig->it_prof_incr = cputime_zero;
871 
872 	sig->leader = 0;	/* session leadership doesn't inherit */
873 	sig->tty_old_pgrp = NULL;
874 
875 	sig->utime = sig->stime = sig->cutime = sig->cstime = cputime_zero;
876 	sig->nvcsw = sig->nivcsw = sig->cnvcsw = sig->cnivcsw = 0;
877 	sig->min_flt = sig->maj_flt = sig->cmin_flt = sig->cmaj_flt = 0;
878 	sig->inblock = sig->oublock = sig->cinblock = sig->coublock = 0;
879 	sig->sched_time = 0;
880 	INIT_LIST_HEAD(&sig->cpu_timers[0]);
881 	INIT_LIST_HEAD(&sig->cpu_timers[1]);
882 	INIT_LIST_HEAD(&sig->cpu_timers[2]);
883 	taskstats_tgid_init(sig);
884 
885 	task_lock(current->group_leader);
886 	memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
887 	task_unlock(current->group_leader);
888 
889 	if (sig->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY) {
890 		/*
891 		 * New sole thread in the process gets an expiry time
892 		 * of the whole CPU time limit.
893 		 */
894 		tsk->it_prof_expires =
895 			secs_to_cputime(sig->rlim[RLIMIT_CPU].rlim_cur);
896 	}
897 	acct_init_pacct(&sig->pacct);
898 
899 	return 0;
900 }
901 
902 void __cleanup_signal(struct signal_struct *sig)
903 {
904 	exit_thread_group_keys(sig);
905 	kmem_cache_free(signal_cachep, sig);
906 }
907 
908 static inline void cleanup_signal(struct task_struct *tsk)
909 {
910 	struct signal_struct *sig = tsk->signal;
911 
912 	atomic_dec(&sig->live);
913 
914 	if (atomic_dec_and_test(&sig->count))
915 		__cleanup_signal(sig);
916 }
917 
918 static inline void copy_flags(unsigned long clone_flags, struct task_struct *p)
919 {
920 	unsigned long new_flags = p->flags;
921 
922 	new_flags &= ~(PF_SUPERPRIV | PF_NOFREEZE);
923 	new_flags |= PF_FORKNOEXEC;
924 	if (!(clone_flags & CLONE_PTRACE))
925 		p->ptrace = 0;
926 	p->flags = new_flags;
927 }
928 
929 asmlinkage long sys_set_tid_address(int __user *tidptr)
930 {
931 	current->clear_child_tid = tidptr;
932 
933 	return current->pid;
934 }
935 
936 static inline void rt_mutex_init_task(struct task_struct *p)
937 {
938 	spin_lock_init(&p->pi_lock);
939 #ifdef CONFIG_RT_MUTEXES
940 	plist_head_init(&p->pi_waiters, &p->pi_lock);
941 	p->pi_blocked_on = NULL;
942 #endif
943 }
944 
945 /*
946  * This creates a new process as a copy of the old one,
947  * but does not actually start it yet.
948  *
949  * It copies the registers, and all the appropriate
950  * parts of the process environment (as per the clone
951  * flags). The actual kick-off is left to the caller.
952  */
953 static struct task_struct *copy_process(unsigned long clone_flags,
954 					unsigned long stack_start,
955 					struct pt_regs *regs,
956 					unsigned long stack_size,
957 					int __user *parent_tidptr,
958 					int __user *child_tidptr,
959 					struct pid *pid)
960 {
961 	int retval;
962 	struct task_struct *p = NULL;
963 
964 	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
965 		return ERR_PTR(-EINVAL);
966 
967 	/*
968 	 * Thread groups must share signals as well, and detached threads
969 	 * can only be started up within the thread group.
970 	 */
971 	if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
972 		return ERR_PTR(-EINVAL);
973 
974 	/*
975 	 * Shared signal handlers imply shared VM. By way of the above,
976 	 * thread groups also imply shared VM. Blocking this case allows
977 	 * for various simplifications in other code.
978 	 */
979 	if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
980 		return ERR_PTR(-EINVAL);
981 
982 	retval = security_task_create(clone_flags);
983 	if (retval)
984 		goto fork_out;
985 
986 	retval = -ENOMEM;
987 	p = dup_task_struct(current);
988 	if (!p)
989 		goto fork_out;
990 
991 	rt_mutex_init_task(p);
992 
993 #ifdef CONFIG_TRACE_IRQFLAGS
994 	DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
995 	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
996 #endif
997 	retval = -EAGAIN;
998 	if (atomic_read(&p->user->processes) >=
999 			p->signal->rlim[RLIMIT_NPROC].rlim_cur) {
1000 		if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
1001 				p->user != &root_user)
1002 			goto bad_fork_free;
1003 	}
1004 
1005 	atomic_inc(&p->user->__count);
1006 	atomic_inc(&p->user->processes);
1007 	get_group_info(p->group_info);
1008 
1009 	/*
1010 	 * If multiple threads are within copy_process(), then this check
1011 	 * triggers too late. This doesn't hurt, the check is only there
1012 	 * to stop root fork bombs.
1013 	 */
1014 	if (nr_threads >= max_threads)
1015 		goto bad_fork_cleanup_count;
1016 
1017 	if (!try_module_get(task_thread_info(p)->exec_domain->module))
1018 		goto bad_fork_cleanup_count;
1019 
1020 	if (p->binfmt && !try_module_get(p->binfmt->module))
1021 		goto bad_fork_cleanup_put_domain;
1022 
1023 	p->did_exec = 0;
1024 	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */
1025 	copy_flags(clone_flags, p);
1026 	p->pid = pid_nr(pid);
1027 	retval = -EFAULT;
1028 	if (clone_flags & CLONE_PARENT_SETTID)
1029 		if (put_user(p->pid, parent_tidptr))
1030 			goto bad_fork_cleanup_delays_binfmt;
1031 
1032 	INIT_LIST_HEAD(&p->children);
1033 	INIT_LIST_HEAD(&p->sibling);
1034 	p->vfork_done = NULL;
1035 	spin_lock_init(&p->alloc_lock);
1036 
1037 	clear_tsk_thread_flag(p, TIF_SIGPENDING);
1038 	init_sigpending(&p->pending);
1039 
1040 	p->utime = cputime_zero;
1041 	p->stime = cputime_zero;
1042  	p->sched_time = 0;
1043 #ifdef CONFIG_TASK_XACCT
1044 	p->rchar = 0;		/* I/O counter: bytes read */
1045 	p->wchar = 0;		/* I/O counter: bytes written */
1046 	p->syscr = 0;		/* I/O counter: read syscalls */
1047 	p->syscw = 0;		/* I/O counter: write syscalls */
1048 #endif
1049 	task_io_accounting_init(p);
1050 	acct_clear_integrals(p);
1051 
1052  	p->it_virt_expires = cputime_zero;
1053 	p->it_prof_expires = cputime_zero;
1054  	p->it_sched_expires = 0;
1055  	INIT_LIST_HEAD(&p->cpu_timers[0]);
1056  	INIT_LIST_HEAD(&p->cpu_timers[1]);
1057  	INIT_LIST_HEAD(&p->cpu_timers[2]);
1058 
1059 	p->lock_depth = -1;		/* -1 = no lock */
1060 	do_posix_clock_monotonic_gettime(&p->start_time);
1061 	p->security = NULL;
1062 	p->io_context = NULL;
1063 	p->io_wait = NULL;
1064 	p->audit_context = NULL;
1065 	cpuset_fork(p);
1066 #ifdef CONFIG_NUMA
1067  	p->mempolicy = mpol_copy(p->mempolicy);
1068  	if (IS_ERR(p->mempolicy)) {
1069  		retval = PTR_ERR(p->mempolicy);
1070  		p->mempolicy = NULL;
1071  		goto bad_fork_cleanup_cpuset;
1072  	}
1073 	mpol_fix_fork_child_flag(p);
1074 #endif
1075 #ifdef CONFIG_TRACE_IRQFLAGS
1076 	p->irq_events = 0;
1077 #ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
1078 	p->hardirqs_enabled = 1;
1079 #else
1080 	p->hardirqs_enabled = 0;
1081 #endif
1082 	p->hardirq_enable_ip = 0;
1083 	p->hardirq_enable_event = 0;
1084 	p->hardirq_disable_ip = _THIS_IP_;
1085 	p->hardirq_disable_event = 0;
1086 	p->softirqs_enabled = 1;
1087 	p->softirq_enable_ip = _THIS_IP_;
1088 	p->softirq_enable_event = 0;
1089 	p->softirq_disable_ip = 0;
1090 	p->softirq_disable_event = 0;
1091 	p->hardirq_context = 0;
1092 	p->softirq_context = 0;
1093 #endif
1094 #ifdef CONFIG_LOCKDEP
1095 	p->lockdep_depth = 0; /* no locks held yet */
1096 	p->curr_chain_key = 0;
1097 	p->lockdep_recursion = 0;
1098 #endif
1099 
1100 #ifdef CONFIG_DEBUG_MUTEXES
1101 	p->blocked_on = NULL; /* not blocked yet */
1102 #endif
1103 
1104 	p->tgid = p->pid;
1105 	if (clone_flags & CLONE_THREAD)
1106 		p->tgid = current->tgid;
1107 
1108 	if ((retval = security_task_alloc(p)))
1109 		goto bad_fork_cleanup_policy;
1110 	if ((retval = audit_alloc(p)))
1111 		goto bad_fork_cleanup_security;
1112 	/* copy all the process information */
1113 	if ((retval = copy_semundo(clone_flags, p)))
1114 		goto bad_fork_cleanup_audit;
1115 	if ((retval = copy_files(clone_flags, p)))
1116 		goto bad_fork_cleanup_semundo;
1117 	if ((retval = copy_fs(clone_flags, p)))
1118 		goto bad_fork_cleanup_files;
1119 	if ((retval = copy_sighand(clone_flags, p)))
1120 		goto bad_fork_cleanup_fs;
1121 	if ((retval = copy_signal(clone_flags, p)))
1122 		goto bad_fork_cleanup_sighand;
1123 	if ((retval = copy_mm(clone_flags, p)))
1124 		goto bad_fork_cleanup_signal;
1125 	if ((retval = copy_keys(clone_flags, p)))
1126 		goto bad_fork_cleanup_mm;
1127 	if ((retval = copy_namespaces(clone_flags, p)))
1128 		goto bad_fork_cleanup_keys;
1129 	retval = copy_thread(0, clone_flags, stack_start, stack_size, p, regs);
1130 	if (retval)
1131 		goto bad_fork_cleanup_namespaces;
1132 
1133 	p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1134 	/*
1135 	 * Clear TID on mm_release()?
1136 	 */
1137 	p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr: NULL;
1138 	p->robust_list = NULL;
1139 #ifdef CONFIG_COMPAT
1140 	p->compat_robust_list = NULL;
1141 #endif
1142 	INIT_LIST_HEAD(&p->pi_state_list);
1143 	p->pi_state_cache = NULL;
1144 
1145 	/*
1146 	 * sigaltstack should be cleared when sharing the same VM
1147 	 */
1148 	if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1149 		p->sas_ss_sp = p->sas_ss_size = 0;
1150 
1151 	/*
1152 	 * Syscall tracing should be turned off in the child regardless
1153 	 * of CLONE_PTRACE.
1154 	 */
1155 	clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1156 #ifdef TIF_SYSCALL_EMU
1157 	clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1158 #endif
1159 
1160 	/* Our parent execution domain becomes current domain
1161 	   These must match for thread signalling to apply */
1162 	p->parent_exec_id = p->self_exec_id;
1163 
1164 	/* ok, now we should be set up.. */
1165 	p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
1166 	p->pdeath_signal = 0;
1167 	p->exit_state = 0;
1168 
1169 	/*
1170 	 * Ok, make it visible to the rest of the system.
1171 	 * We dont wake it up yet.
1172 	 */
1173 	p->group_leader = p;
1174 	INIT_LIST_HEAD(&p->thread_group);
1175 	INIT_LIST_HEAD(&p->ptrace_children);
1176 	INIT_LIST_HEAD(&p->ptrace_list);
1177 
1178 	/* Perform scheduler related setup. Assign this task to a CPU. */
1179 	sched_fork(p, clone_flags);
1180 
1181 	/* Need tasklist lock for parent etc handling! */
1182 	write_lock_irq(&tasklist_lock);
1183 
1184 	/* for sys_ioprio_set(IOPRIO_WHO_PGRP) */
1185 	p->ioprio = current->ioprio;
1186 
1187 	/*
1188 	 * The task hasn't been attached yet, so its cpus_allowed mask will
1189 	 * not be changed, nor will its assigned CPU.
1190 	 *
1191 	 * The cpus_allowed mask of the parent may have changed after it was
1192 	 * copied first time - so re-copy it here, then check the child's CPU
1193 	 * to ensure it is on a valid CPU (and if not, just force it back to
1194 	 * parent's CPU). This avoids alot of nasty races.
1195 	 */
1196 	p->cpus_allowed = current->cpus_allowed;
1197 	if (unlikely(!cpu_isset(task_cpu(p), p->cpus_allowed) ||
1198 			!cpu_online(task_cpu(p))))
1199 		set_task_cpu(p, smp_processor_id());
1200 
1201 	/* CLONE_PARENT re-uses the old parent */
1202 	if (clone_flags & (CLONE_PARENT|CLONE_THREAD))
1203 		p->real_parent = current->real_parent;
1204 	else
1205 		p->real_parent = current;
1206 	p->parent = p->real_parent;
1207 
1208 	spin_lock(&current->sighand->siglock);
1209 
1210 	/*
1211 	 * Process group and session signals need to be delivered to just the
1212 	 * parent before the fork or both the parent and the child after the
1213 	 * fork. Restart if a signal comes in before we add the new process to
1214 	 * it's process group.
1215 	 * A fatal signal pending means that current will exit, so the new
1216 	 * thread can't slip out of an OOM kill (or normal SIGKILL).
1217  	 */
1218  	recalc_sigpending();
1219 	if (signal_pending(current)) {
1220 		spin_unlock(&current->sighand->siglock);
1221 		write_unlock_irq(&tasklist_lock);
1222 		retval = -ERESTARTNOINTR;
1223 		goto bad_fork_cleanup_namespaces;
1224 	}
1225 
1226 	if (clone_flags & CLONE_THREAD) {
1227 		p->group_leader = current->group_leader;
1228 		list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);
1229 
1230 		if (!cputime_eq(current->signal->it_virt_expires,
1231 				cputime_zero) ||
1232 		    !cputime_eq(current->signal->it_prof_expires,
1233 				cputime_zero) ||
1234 		    current->signal->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY ||
1235 		    !list_empty(&current->signal->cpu_timers[0]) ||
1236 		    !list_empty(&current->signal->cpu_timers[1]) ||
1237 		    !list_empty(&current->signal->cpu_timers[2])) {
1238 			/*
1239 			 * Have child wake up on its first tick to check
1240 			 * for process CPU timers.
1241 			 */
1242 			p->it_prof_expires = jiffies_to_cputime(1);
1243 		}
1244 	}
1245 
1246 	if (likely(p->pid)) {
1247 		add_parent(p);
1248 		if (unlikely(p->ptrace & PT_PTRACED))
1249 			__ptrace_link(p, current->parent);
1250 
1251 		if (thread_group_leader(p)) {
1252 			p->signal->tty = current->signal->tty;
1253 			p->signal->pgrp = process_group(current);
1254 			set_signal_session(p->signal, process_session(current));
1255 			attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
1256 			attach_pid(p, PIDTYPE_SID, task_session(current));
1257 
1258 			list_add_tail_rcu(&p->tasks, &init_task.tasks);
1259 			__get_cpu_var(process_counts)++;
1260 		}
1261 		attach_pid(p, PIDTYPE_PID, pid);
1262 		nr_threads++;
1263 	}
1264 
1265 	total_forks++;
1266 	spin_unlock(&current->sighand->siglock);
1267 	write_unlock_irq(&tasklist_lock);
1268 	proc_fork_connector(p);
1269 	return p;
1270 
1271 bad_fork_cleanup_namespaces:
1272 	exit_task_namespaces(p);
1273 bad_fork_cleanup_keys:
1274 	exit_keys(p);
1275 bad_fork_cleanup_mm:
1276 	if (p->mm)
1277 		mmput(p->mm);
1278 bad_fork_cleanup_signal:
1279 	cleanup_signal(p);
1280 bad_fork_cleanup_sighand:
1281 	__cleanup_sighand(p->sighand);
1282 bad_fork_cleanup_fs:
1283 	exit_fs(p); /* blocking */
1284 bad_fork_cleanup_files:
1285 	exit_files(p); /* blocking */
1286 bad_fork_cleanup_semundo:
1287 	exit_sem(p);
1288 bad_fork_cleanup_audit:
1289 	audit_free(p);
1290 bad_fork_cleanup_security:
1291 	security_task_free(p);
1292 bad_fork_cleanup_policy:
1293 #ifdef CONFIG_NUMA
1294 	mpol_free(p->mempolicy);
1295 bad_fork_cleanup_cpuset:
1296 #endif
1297 	cpuset_exit(p);
1298 bad_fork_cleanup_delays_binfmt:
1299 	delayacct_tsk_free(p);
1300 	if (p->binfmt)
1301 		module_put(p->binfmt->module);
1302 bad_fork_cleanup_put_domain:
1303 	module_put(task_thread_info(p)->exec_domain->module);
1304 bad_fork_cleanup_count:
1305 	put_group_info(p->group_info);
1306 	atomic_dec(&p->user->processes);
1307 	free_uid(p->user);
1308 bad_fork_free:
1309 	free_task(p);
1310 fork_out:
1311 	return ERR_PTR(retval);
1312 }
1313 
1314 noinline struct pt_regs * __devinit __attribute__((weak)) idle_regs(struct pt_regs *regs)
1315 {
1316 	memset(regs, 0, sizeof(struct pt_regs));
1317 	return regs;
1318 }
1319 
1320 struct task_struct * __cpuinit fork_idle(int cpu)
1321 {
1322 	struct task_struct *task;
1323 	struct pt_regs regs;
1324 
1325 	task = copy_process(CLONE_VM, 0, idle_regs(&regs), 0, NULL, NULL,
1326 				&init_struct_pid);
1327 	if (!IS_ERR(task))
1328 		init_idle(task, cpu);
1329 
1330 	return task;
1331 }
1332 
1333 static inline int fork_traceflag (unsigned clone_flags)
1334 {
1335 	if (clone_flags & CLONE_UNTRACED)
1336 		return 0;
1337 	else if (clone_flags & CLONE_VFORK) {
1338 		if (current->ptrace & PT_TRACE_VFORK)
1339 			return PTRACE_EVENT_VFORK;
1340 	} else if ((clone_flags & CSIGNAL) != SIGCHLD) {
1341 		if (current->ptrace & PT_TRACE_CLONE)
1342 			return PTRACE_EVENT_CLONE;
1343 	} else if (current->ptrace & PT_TRACE_FORK)
1344 		return PTRACE_EVENT_FORK;
1345 
1346 	return 0;
1347 }
1348 
1349 /*
1350  *  Ok, this is the main fork-routine.
1351  *
1352  * It copies the process, and if successful kick-starts
1353  * it and waits for it to finish using the VM if required.
1354  */
1355 long do_fork(unsigned long clone_flags,
1356 	      unsigned long stack_start,
1357 	      struct pt_regs *regs,
1358 	      unsigned long stack_size,
1359 	      int __user *parent_tidptr,
1360 	      int __user *child_tidptr)
1361 {
1362 	struct task_struct *p;
1363 	int trace = 0;
1364 	struct pid *pid = alloc_pid();
1365 	long nr;
1366 
1367 	if (!pid)
1368 		return -EAGAIN;
1369 	nr = pid->nr;
1370 	if (unlikely(current->ptrace)) {
1371 		trace = fork_traceflag (clone_flags);
1372 		if (trace)
1373 			clone_flags |= CLONE_PTRACE;
1374 	}
1375 
1376 	p = copy_process(clone_flags, stack_start, regs, stack_size, parent_tidptr, child_tidptr, pid);
1377 	/*
1378 	 * Do this prior waking up the new thread - the thread pointer
1379 	 * might get invalid after that point, if the thread exits quickly.
1380 	 */
1381 	if (!IS_ERR(p)) {
1382 		struct completion vfork;
1383 
1384 		if (clone_flags & CLONE_VFORK) {
1385 			p->vfork_done = &vfork;
1386 			init_completion(&vfork);
1387 		}
1388 
1389 		if ((p->ptrace & PT_PTRACED) || (clone_flags & CLONE_STOPPED)) {
1390 			/*
1391 			 * We'll start up with an immediate SIGSTOP.
1392 			 */
1393 			sigaddset(&p->pending.signal, SIGSTOP);
1394 			set_tsk_thread_flag(p, TIF_SIGPENDING);
1395 		}
1396 
1397 		if (!(clone_flags & CLONE_STOPPED))
1398 			wake_up_new_task(p, clone_flags);
1399 		else
1400 			p->state = TASK_STOPPED;
1401 
1402 		if (unlikely (trace)) {
1403 			current->ptrace_message = nr;
1404 			ptrace_notify ((trace << 8) | SIGTRAP);
1405 		}
1406 
1407 		if (clone_flags & CLONE_VFORK) {
1408 			wait_for_completion(&vfork);
1409 			if (unlikely (current->ptrace & PT_TRACE_VFORK_DONE)) {
1410 				current->ptrace_message = nr;
1411 				ptrace_notify ((PTRACE_EVENT_VFORK_DONE << 8) | SIGTRAP);
1412 			}
1413 		}
1414 	} else {
1415 		free_pid(pid);
1416 		nr = PTR_ERR(p);
1417 	}
1418 	return nr;
1419 }
1420 
1421 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1422 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1423 #endif
1424 
1425 static void sighand_ctor(void *data, struct kmem_cache *cachep,
1426 			unsigned long flags)
1427 {
1428 	struct sighand_struct *sighand = data;
1429 
1430 	if (flags & SLAB_CTOR_CONSTRUCTOR) {
1431 		spin_lock_init(&sighand->siglock);
1432 		INIT_LIST_HEAD(&sighand->signalfd_list);
1433 	}
1434 }
1435 
1436 void __init proc_caches_init(void)
1437 {
1438 	sighand_cachep = kmem_cache_create("sighand_cache",
1439 			sizeof(struct sighand_struct), 0,
1440 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU,
1441 			sighand_ctor, NULL);
1442 	signal_cachep = kmem_cache_create("signal_cache",
1443 			sizeof(struct signal_struct), 0,
1444 			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
1445 	files_cachep = kmem_cache_create("files_cache",
1446 			sizeof(struct files_struct), 0,
1447 			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
1448 	fs_cachep = kmem_cache_create("fs_cache",
1449 			sizeof(struct fs_struct), 0,
1450 			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
1451 	vm_area_cachep = kmem_cache_create("vm_area_struct",
1452 			sizeof(struct vm_area_struct), 0,
1453 			SLAB_PANIC, NULL, NULL);
1454 	mm_cachep = kmem_cache_create("mm_struct",
1455 			sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1456 			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
1457 }
1458 
1459 /*
1460  * Check constraints on flags passed to the unshare system call and
1461  * force unsharing of additional process context as appropriate.
1462  */
1463 static inline void check_unshare_flags(unsigned long *flags_ptr)
1464 {
1465 	/*
1466 	 * If unsharing a thread from a thread group, must also
1467 	 * unshare vm.
1468 	 */
1469 	if (*flags_ptr & CLONE_THREAD)
1470 		*flags_ptr |= CLONE_VM;
1471 
1472 	/*
1473 	 * If unsharing vm, must also unshare signal handlers.
1474 	 */
1475 	if (*flags_ptr & CLONE_VM)
1476 		*flags_ptr |= CLONE_SIGHAND;
1477 
1478 	/*
1479 	 * If unsharing signal handlers and the task was created
1480 	 * using CLONE_THREAD, then must unshare the thread
1481 	 */
1482 	if ((*flags_ptr & CLONE_SIGHAND) &&
1483 	    (atomic_read(&current->signal->count) > 1))
1484 		*flags_ptr |= CLONE_THREAD;
1485 
1486 	/*
1487 	 * If unsharing namespace, must also unshare filesystem information.
1488 	 */
1489 	if (*flags_ptr & CLONE_NEWNS)
1490 		*flags_ptr |= CLONE_FS;
1491 }
1492 
1493 /*
1494  * Unsharing of tasks created with CLONE_THREAD is not supported yet
1495  */
1496 static int unshare_thread(unsigned long unshare_flags)
1497 {
1498 	if (unshare_flags & CLONE_THREAD)
1499 		return -EINVAL;
1500 
1501 	return 0;
1502 }
1503 
1504 /*
1505  * Unshare the filesystem structure if it is being shared
1506  */
1507 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1508 {
1509 	struct fs_struct *fs = current->fs;
1510 
1511 	if ((unshare_flags & CLONE_FS) &&
1512 	    (fs && atomic_read(&fs->count) > 1)) {
1513 		*new_fsp = __copy_fs_struct(current->fs);
1514 		if (!*new_fsp)
1515 			return -ENOMEM;
1516 	}
1517 
1518 	return 0;
1519 }
1520 
1521 /*
1522  * Unsharing of sighand is not supported yet
1523  */
1524 static int unshare_sighand(unsigned long unshare_flags, struct sighand_struct **new_sighp)
1525 {
1526 	struct sighand_struct *sigh = current->sighand;
1527 
1528 	if ((unshare_flags & CLONE_SIGHAND) && atomic_read(&sigh->count) > 1)
1529 		return -EINVAL;
1530 	else
1531 		return 0;
1532 }
1533 
1534 /*
1535  * Unshare vm if it is being shared
1536  */
1537 static int unshare_vm(unsigned long unshare_flags, struct mm_struct **new_mmp)
1538 {
1539 	struct mm_struct *mm = current->mm;
1540 
1541 	if ((unshare_flags & CLONE_VM) &&
1542 	    (mm && atomic_read(&mm->mm_users) > 1)) {
1543 		return -EINVAL;
1544 	}
1545 
1546 	return 0;
1547 }
1548 
1549 /*
1550  * Unshare file descriptor table if it is being shared
1551  */
1552 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1553 {
1554 	struct files_struct *fd = current->files;
1555 	int error = 0;
1556 
1557 	if ((unshare_flags & CLONE_FILES) &&
1558 	    (fd && atomic_read(&fd->count) > 1)) {
1559 		*new_fdp = dup_fd(fd, &error);
1560 		if (!*new_fdp)
1561 			return error;
1562 	}
1563 
1564 	return 0;
1565 }
1566 
1567 /*
1568  * Unsharing of semundo for tasks created with CLONE_SYSVSEM is not
1569  * supported yet
1570  */
1571 static int unshare_semundo(unsigned long unshare_flags, struct sem_undo_list **new_ulistp)
1572 {
1573 	if (unshare_flags & CLONE_SYSVSEM)
1574 		return -EINVAL;
1575 
1576 	return 0;
1577 }
1578 
1579 /*
1580  * unshare allows a process to 'unshare' part of the process
1581  * context which was originally shared using clone.  copy_*
1582  * functions used by do_fork() cannot be used here directly
1583  * because they modify an inactive task_struct that is being
1584  * constructed. Here we are modifying the current, active,
1585  * task_struct.
1586  */
1587 asmlinkage long sys_unshare(unsigned long unshare_flags)
1588 {
1589 	int err = 0;
1590 	struct fs_struct *fs, *new_fs = NULL;
1591 	struct sighand_struct *new_sigh = NULL;
1592 	struct mm_struct *mm, *new_mm = NULL, *active_mm = NULL;
1593 	struct files_struct *fd, *new_fd = NULL;
1594 	struct sem_undo_list *new_ulist = NULL;
1595 	struct nsproxy *new_nsproxy = NULL, *old_nsproxy = NULL;
1596 
1597 	check_unshare_flags(&unshare_flags);
1598 
1599 	/* Return -EINVAL for all unsupported flags */
1600 	err = -EINVAL;
1601 	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1602 				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1603 				CLONE_NEWUTS|CLONE_NEWIPC))
1604 		goto bad_unshare_out;
1605 
1606 	if ((err = unshare_thread(unshare_flags)))
1607 		goto bad_unshare_out;
1608 	if ((err = unshare_fs(unshare_flags, &new_fs)))
1609 		goto bad_unshare_cleanup_thread;
1610 	if ((err = unshare_sighand(unshare_flags, &new_sigh)))
1611 		goto bad_unshare_cleanup_fs;
1612 	if ((err = unshare_vm(unshare_flags, &new_mm)))
1613 		goto bad_unshare_cleanup_sigh;
1614 	if ((err = unshare_fd(unshare_flags, &new_fd)))
1615 		goto bad_unshare_cleanup_vm;
1616 	if ((err = unshare_semundo(unshare_flags, &new_ulist)))
1617 		goto bad_unshare_cleanup_fd;
1618 	if ((err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
1619 			new_fs)))
1620 		goto bad_unshare_cleanup_semundo;
1621 
1622 	if (new_fs ||  new_mm || new_fd || new_ulist || new_nsproxy) {
1623 
1624 		task_lock(current);
1625 
1626 		if (new_nsproxy) {
1627 			old_nsproxy = current->nsproxy;
1628 			current->nsproxy = new_nsproxy;
1629 			new_nsproxy = old_nsproxy;
1630 		}
1631 
1632 		if (new_fs) {
1633 			fs = current->fs;
1634 			current->fs = new_fs;
1635 			new_fs = fs;
1636 		}
1637 
1638 		if (new_mm) {
1639 			mm = current->mm;
1640 			active_mm = current->active_mm;
1641 			current->mm = new_mm;
1642 			current->active_mm = new_mm;
1643 			activate_mm(active_mm, new_mm);
1644 			new_mm = mm;
1645 		}
1646 
1647 		if (new_fd) {
1648 			fd = current->files;
1649 			current->files = new_fd;
1650 			new_fd = fd;
1651 		}
1652 
1653 		task_unlock(current);
1654 	}
1655 
1656 	if (new_nsproxy)
1657 		put_nsproxy(new_nsproxy);
1658 
1659 bad_unshare_cleanup_semundo:
1660 bad_unshare_cleanup_fd:
1661 	if (new_fd)
1662 		put_files_struct(new_fd);
1663 
1664 bad_unshare_cleanup_vm:
1665 	if (new_mm)
1666 		mmput(new_mm);
1667 
1668 bad_unshare_cleanup_sigh:
1669 	if (new_sigh)
1670 		if (atomic_dec_and_test(&new_sigh->count))
1671 			kmem_cache_free(sighand_cachep, new_sigh);
1672 
1673 bad_unshare_cleanup_fs:
1674 	if (new_fs)
1675 		put_fs_struct(new_fs);
1676 
1677 bad_unshare_cleanup_thread:
1678 bad_unshare_out:
1679 	return err;
1680 }
1681