fork.c 40.7 KB
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/*
 *  linux/kernel/fork.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

/*
 *  'fork.c' contains the help-routines for the 'fork' system call
 * (see also entry.S and others).
 * Fork is rather simple, once you get the hang of it, but the memory
 * management can be a bitch. See 'mm/memory.c': 'copy_page_range()'
 */

#include <linux/slab.h>
#include <linux/init.h>
#include <linux/unistd.h>
#include <linux/module.h>
#include <linux/vmalloc.h>
#include <linux/completion.h>
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#include <linux/mnt_namespace.h>
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#include <linux/personality.h>
#include <linux/mempolicy.h>
#include <linux/sem.h>
#include <linux/file.h>
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#include <linux/fdtable.h>
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#include <linux/iocontext.h>
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#include <linux/key.h>
#include <linux/binfmts.h>
#include <linux/mman.h>
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#include <linux/mmu_notifier.h>
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#include <linux/fs.h>
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#include <linux/nsproxy.h>
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#include <linux/capability.h>
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#include <linux/cpu.h>
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#include <linux/cgroup.h>
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#include <linux/security.h>
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#include <linux/hugetlb.h>
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#include <linux/swap.h>
#include <linux/syscalls.h>
#include <linux/jiffies.h>
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#include <linux/tracehook.h>
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#include <linux/futex.h>
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#include <linux/task_io_accounting_ops.h>
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#include <linux/rcupdate.h>
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#include <linux/ptrace.h>
#include <linux/mount.h>
#include <linux/audit.h>
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#include <linux/memcontrol.h>
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#include <linux/profile.h>
#include <linux/rmap.h>
#include <linux/acct.h>
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#include <linux/tsacct_kern.h>
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#include <linux/cn_proc.h>
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#include <linux/freezer.h>
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#include <linux/delayacct.h>
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#include <linux/taskstats_kern.h>
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#include <linux/random.h>
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#include <linux/tty.h>
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#include <linux/proc_fs.h>
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#include <linux/blkdev.h>
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#include <asm/pgtable.h>
#include <asm/pgalloc.h>
#include <asm/uaccess.h>
#include <asm/mmu_context.h>
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>

/*
 * Protected counters by write_lock_irq(&tasklist_lock)
 */
unsigned long total_forks;	/* Handle normal Linux uptimes. */
int nr_threads; 		/* The idle threads do not count.. */

int max_threads;		/* tunable limit on nr_threads */

DEFINE_PER_CPU(unsigned long, process_counts) = 0;

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__cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
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int nr_processes(void)
{
	int cpu;
	int total = 0;

	for_each_online_cpu(cpu)
		total += per_cpu(process_counts, cpu);

	return total;
}

#ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
# define alloc_task_struct()	kmem_cache_alloc(task_struct_cachep, GFP_KERNEL)
# define free_task_struct(tsk)	kmem_cache_free(task_struct_cachep, (tsk))
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static struct kmem_cache *task_struct_cachep;
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#endif

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#ifndef __HAVE_ARCH_THREAD_INFO_ALLOCATOR
static inline struct thread_info *alloc_thread_info(struct task_struct *tsk)
{
#ifdef CONFIG_DEBUG_STACK_USAGE
	gfp_t mask = GFP_KERNEL | __GFP_ZERO;
#else
	gfp_t mask = GFP_KERNEL;
#endif
	return (struct thread_info *)__get_free_pages(mask, THREAD_SIZE_ORDER);
}

static inline void free_thread_info(struct thread_info *ti)
{
	free_pages((unsigned long)ti, THREAD_SIZE_ORDER);
}
#endif

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/* SLAB cache for signal_struct structures (tsk->signal) */
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static struct kmem_cache *signal_cachep;
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/* SLAB cache for sighand_struct structures (tsk->sighand) */
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struct kmem_cache *sighand_cachep;
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/* SLAB cache for files_struct structures (tsk->files) */
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struct kmem_cache *files_cachep;
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/* SLAB cache for fs_struct structures (tsk->fs) */
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struct kmem_cache *fs_cachep;
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/* SLAB cache for vm_area_struct structures */
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struct kmem_cache *vm_area_cachep;
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/* SLAB cache for mm_struct structures (tsk->mm) */
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static struct kmem_cache *mm_cachep;
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void free_task(struct task_struct *tsk)
{
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	prop_local_destroy_single(&tsk->dirties);
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	free_thread_info(tsk->stack);
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	rt_mutex_debug_task_free(tsk);
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	free_task_struct(tsk);
}
EXPORT_SYMBOL(free_task);

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void __put_task_struct(struct task_struct *tsk)
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{
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	WARN_ON(!tsk->exit_state);
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	WARN_ON(atomic_read(&tsk->usage));
	WARN_ON(tsk == current);

	security_task_free(tsk);
	free_uid(tsk->user);
	put_group_info(tsk->group_info);
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	delayacct_tsk_free(tsk);
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	if (!profile_handoff_task(tsk))
		free_task(tsk);
}

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/*
 * macro override instead of weak attribute alias, to workaround
 * gcc 4.1.0 and 4.1.1 bugs with weak attribute and empty functions.
 */
#ifndef arch_task_cache_init
#define arch_task_cache_init()
#endif
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void __init fork_init(unsigned long mempages)
{
#ifndef __HAVE_ARCH_TASK_STRUCT_ALLOCATOR
#ifndef ARCH_MIN_TASKALIGN
#define ARCH_MIN_TASKALIGN	L1_CACHE_BYTES
#endif
	/* create a slab on which task_structs can be allocated */
	task_struct_cachep =
		kmem_cache_create("task_struct", sizeof(struct task_struct),
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			ARCH_MIN_TASKALIGN, SLAB_PANIC, NULL);
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#endif

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	/* do the arch specific task caches init */
	arch_task_cache_init();

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	/*
	 * The default maximum number of threads is set to a safe
	 * value: the thread structures can take up at most half
	 * of memory.
	 */
	max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);

	/*
	 * we need to allow at least 20 threads to boot a system
	 */
	if(max_threads < 20)
		max_threads = 20;

	init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
	init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
	init_task.signal->rlim[RLIMIT_SIGPENDING] =
		init_task.signal->rlim[RLIMIT_NPROC];
}

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int __attribute__((weak)) arch_dup_task_struct(struct task_struct *dst,
					       struct task_struct *src)
{
	*dst = *src;
	return 0;
}

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static struct task_struct *dup_task_struct(struct task_struct *orig)
{
	struct task_struct *tsk;
	struct thread_info *ti;
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	int err;
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	prepare_to_copy(orig);

	tsk = alloc_task_struct();
	if (!tsk)
		return NULL;

	ti = alloc_thread_info(tsk);
	if (!ti) {
		free_task_struct(tsk);
		return NULL;
	}

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 	err = arch_dup_task_struct(tsk, orig);
	if (err)
		goto out;

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	tsk->stack = ti;
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	err = prop_local_init_single(&tsk->dirties);
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	if (err)
		goto out;
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	setup_thread_stack(tsk, orig);
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#ifdef CONFIG_CC_STACKPROTECTOR
	tsk->stack_canary = get_random_int();
#endif

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	/* One for us, one for whoever does the "release_task()" (usually parent) */
	atomic_set(&tsk->usage,2);
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	atomic_set(&tsk->fs_excl, 0);
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#ifdef CONFIG_BLK_DEV_IO_TRACE
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	tsk->btrace_seq = 0;
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#endif
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	tsk->splice_pipe = NULL;
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	return tsk;
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out:
	free_thread_info(ti);
	free_task_struct(tsk);
	return NULL;
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}

#ifdef CONFIG_MMU
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static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
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{
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	struct vm_area_struct *mpnt, *tmp, **pprev;
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	struct rb_node **rb_link, *rb_parent;
	int retval;
	unsigned long charge;
	struct mempolicy *pol;

	down_write(&oldmm->mmap_sem);
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	flush_cache_dup_mm(oldmm);
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	/*
	 * Not linked in yet - no deadlock potential:
	 */
	down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
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	mm->locked_vm = 0;
	mm->mmap = NULL;
	mm->mmap_cache = NULL;
	mm->free_area_cache = oldmm->mmap_base;
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	mm->cached_hole_size = ~0UL;
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	mm->map_count = 0;
	cpus_clear(mm->cpu_vm_mask);
	mm->mm_rb = RB_ROOT;
	rb_link = &mm->mm_rb.rb_node;
	rb_parent = NULL;
	pprev = &mm->mmap;

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	for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
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		struct file *file;

		if (mpnt->vm_flags & VM_DONTCOPY) {
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			long pages = vma_pages(mpnt);
			mm->total_vm -= pages;
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			vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
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								-pages);
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			continue;
		}
		charge = 0;
		if (mpnt->vm_flags & VM_ACCOUNT) {
			unsigned int len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
			if (security_vm_enough_memory(len))
				goto fail_nomem;
			charge = len;
		}
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		tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
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		if (!tmp)
			goto fail_nomem;
		*tmp = *mpnt;
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		pol = mpol_dup(vma_policy(mpnt));
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		retval = PTR_ERR(pol);
		if (IS_ERR(pol))
			goto fail_nomem_policy;
		vma_set_policy(tmp, pol);
		tmp->vm_flags &= ~VM_LOCKED;
		tmp->vm_mm = mm;
		tmp->vm_next = NULL;
		anon_vma_link(tmp);
		file = tmp->vm_file;
		if (file) {
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			struct inode *inode = file->f_path.dentry->d_inode;
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			get_file(file);
			if (tmp->vm_flags & VM_DENYWRITE)
				atomic_dec(&inode->i_writecount);
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			/* insert tmp into the share list, just after mpnt */
			spin_lock(&file->f_mapping->i_mmap_lock);
			tmp->vm_truncate_count = mpnt->vm_truncate_count;
			flush_dcache_mmap_lock(file->f_mapping);
			vma_prio_tree_add(tmp, mpnt);
			flush_dcache_mmap_unlock(file->f_mapping);
			spin_unlock(&file->f_mapping->i_mmap_lock);
		}

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		/*
		 * Clear hugetlb-related page reserves for children. This only
		 * affects MAP_PRIVATE mappings. Faults generated by the child
		 * are not guaranteed to succeed, even if read-only
		 */
		if (is_vm_hugetlb_page(tmp))
			reset_vma_resv_huge_pages(tmp);

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		/*
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		 * Link in the new vma and copy the page table entries.
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		 */
		*pprev = tmp;
		pprev = &tmp->vm_next;

		__vma_link_rb(mm, tmp, rb_link, rb_parent);
		rb_link = &tmp->vm_rb.rb_right;
		rb_parent = &tmp->vm_rb;

		mm->map_count++;
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		retval = copy_page_range(mm, oldmm, mpnt);
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		if (tmp->vm_ops && tmp->vm_ops->open)
			tmp->vm_ops->open(tmp);

		if (retval)
			goto out;
	}
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	/* a new mm has just been created */
	arch_dup_mmap(oldmm, mm);
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	retval = 0;
out:
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	up_write(&mm->mmap_sem);
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	flush_tlb_mm(oldmm);
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	up_write(&oldmm->mmap_sem);
	return retval;
fail_nomem_policy:
	kmem_cache_free(vm_area_cachep, tmp);
fail_nomem:
	retval = -ENOMEM;
	vm_unacct_memory(charge);
	goto out;
}

static inline int mm_alloc_pgd(struct mm_struct * mm)
{
	mm->pgd = pgd_alloc(mm);
	if (unlikely(!mm->pgd))
		return -ENOMEM;
	return 0;
}

static inline void mm_free_pgd(struct mm_struct * mm)
{
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	pgd_free(mm, mm->pgd);
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}
#else
#define dup_mmap(mm, oldmm)	(0)
#define mm_alloc_pgd(mm)	(0)
#define mm_free_pgd(mm)
#endif /* CONFIG_MMU */

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__cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
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#define allocate_mm()	(kmem_cache_alloc(mm_cachep, GFP_KERNEL))
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#define free_mm(mm)	(kmem_cache_free(mm_cachep, (mm)))

#include <linux/init_task.h>

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static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
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{
	atomic_set(&mm->mm_users, 1);
	atomic_set(&mm->mm_count, 1);
	init_rwsem(&mm->mmap_sem);
	INIT_LIST_HEAD(&mm->mmlist);
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	mm->flags = (current->mm) ? current->mm->flags
				  : MMF_DUMP_FILTER_DEFAULT;
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	mm->core_state = NULL;
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	mm->nr_ptes = 0;
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	set_mm_counter(mm, file_rss, 0);
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	set_mm_counter(mm, anon_rss, 0);
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	spin_lock_init(&mm->page_table_lock);
	rwlock_init(&mm->ioctx_list_lock);
	mm->ioctx_list = NULL;
	mm->free_area_cache = TASK_UNMAPPED_BASE;
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	mm->cached_hole_size = ~0UL;
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	mm_init_owner(mm, p);
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	if (likely(!mm_alloc_pgd(mm))) {
		mm->def_flags = 0;
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		mmu_notifier_mm_init(mm);
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		return mm;
	}
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	free_mm(mm);
	return NULL;
}

/*
 * Allocate and initialize an mm_struct.
 */
struct mm_struct * mm_alloc(void)
{
	struct mm_struct * mm;

	mm = allocate_mm();
	if (mm) {
		memset(mm, 0, sizeof(*mm));
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		mm = mm_init(mm, current);
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	}
	return mm;
}

/*
 * Called when the last reference to the mm
 * is dropped: either by a lazy thread or by
 * mmput. Free the page directory and the mm.
 */
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void __mmdrop(struct mm_struct *mm)
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{
	BUG_ON(mm == &init_mm);
	mm_free_pgd(mm);
	destroy_context(mm);
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	mmu_notifier_mm_destroy(mm);
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	free_mm(mm);
}
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EXPORT_SYMBOL_GPL(__mmdrop);
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/*
 * Decrement the use count and release all resources for an mm.
 */
void mmput(struct mm_struct *mm)
{
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	might_sleep();

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	if (atomic_dec_and_test(&mm->mm_users)) {
		exit_aio(mm);
		exit_mmap(mm);
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		set_mm_exe_file(mm, NULL);
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		if (!list_empty(&mm->mmlist)) {
			spin_lock(&mmlist_lock);
			list_del(&mm->mmlist);
			spin_unlock(&mmlist_lock);
		}
		put_swap_token(mm);
		mmdrop(mm);
	}
}
EXPORT_SYMBOL_GPL(mmput);

/**
 * get_task_mm - acquire a reference to the task's mm
 *
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 * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
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 * this kernel workthread has transiently adopted a user mm with use_mm,
 * to do its AIO) is not set and if so returns a reference to it, after
 * bumping up the use count.  User must release the mm via mmput()
 * after use.  Typically used by /proc and ptrace.
 */
struct mm_struct *get_task_mm(struct task_struct *task)
{
	struct mm_struct *mm;

	task_lock(task);
	mm = task->mm;
	if (mm) {
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		if (task->flags & PF_KTHREAD)
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			mm = NULL;
		else
			atomic_inc(&mm->mm_users);
	}
	task_unlock(task);
	return mm;
}
EXPORT_SYMBOL_GPL(get_task_mm);

/* Please note the differences between mmput and mm_release.
 * mmput is called whenever we stop holding onto a mm_struct,
 * error success whatever.
 *
 * mm_release is called after a mm_struct has been removed
 * from the current process.
 *
 * This difference is important for error handling, when we
 * only half set up a mm_struct for a new process and need to restore
 * the old one.  Because we mmput the new mm_struct before
 * restoring the old one. . .
 * Eric Biederman 10 January 1998
 */
void mm_release(struct task_struct *tsk, struct mm_struct *mm)
{
	struct completion *vfork_done = tsk->vfork_done;

	/* Get rid of any cached register state */
	deactivate_mm(tsk, mm);

	/* notify parent sleeping on vfork() */
	if (vfork_done) {
		tsk->vfork_done = NULL;
		complete(vfork_done);
	}
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	/*
	 * If we're exiting normally, clear a user-space tid field if
	 * requested.  We leave this alone when dying by signal, to leave
	 * the value intact in a core dump, and to save the unnecessary
	 * trouble otherwise.  Userland only wants this done for a sys_exit.
	 */
	if (tsk->clear_child_tid
	    && !(tsk->flags & PF_SIGNALED)
	    && atomic_read(&mm->mm_users) > 1) {
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		u32 __user * tidptr = tsk->clear_child_tid;
		tsk->clear_child_tid = NULL;

		/*
		 * We don't check the error code - if userspace has
		 * not set up a proper pointer then tough luck.
		 */
		put_user(0, tidptr);
		sys_futex(tidptr, FUTEX_WAKE, 1, NULL, NULL, 0);
	}
}

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/*
 * Allocate a new mm structure and copy contents from the
 * mm structure of the passed in task structure.
 */
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struct mm_struct *dup_mm(struct task_struct *tsk)
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{
	struct mm_struct *mm, *oldmm = current->mm;
	int err;

	if (!oldmm)
		return NULL;

	mm = allocate_mm();
	if (!mm)
		goto fail_nomem;

	memcpy(mm, oldmm, sizeof(*mm));

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	/* Initializing for Swap token stuff */
	mm->token_priority = 0;
	mm->last_interval = 0;

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	if (!mm_init(mm, tsk))
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		goto fail_nomem;

	if (init_new_context(tsk, mm))
		goto fail_nocontext;

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	dup_mm_exe_file(oldmm, mm);

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	err = dup_mmap(mm, oldmm);
	if (err)
		goto free_pt;

	mm->hiwater_rss = get_mm_rss(mm);
	mm->hiwater_vm = mm->total_vm;

	return mm;

free_pt:
	mmput(mm);

fail_nomem:
	return NULL;

fail_nocontext:
	/*
	 * If init_new_context() failed, we cannot use mmput() to free the mm
	 * because it calls destroy_context()
	 */
	mm_free_pgd(mm);
	free_mm(mm);
	return NULL;
}

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static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
{
	struct mm_struct * mm, *oldmm;
	int retval;

	tsk->min_flt = tsk->maj_flt = 0;
	tsk->nvcsw = tsk->nivcsw = 0;

	tsk->mm = NULL;
	tsk->active_mm = NULL;

	/*
	 * Are we cloning a kernel thread?
	 *
	 * We need to steal a active VM for that..
	 */
	oldmm = current->mm;
	if (!oldmm)
		return 0;

	if (clone_flags & CLONE_VM) {
		atomic_inc(&oldmm->mm_users);
		mm = oldmm;
		goto good_mm;
	}

	retval = -ENOMEM;
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	mm = dup_mm(tsk);
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	if (!mm)
		goto fail_nomem;

good_mm:
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	/* Initializing for Swap token stuff */
	mm->token_priority = 0;
	mm->last_interval = 0;

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	tsk->mm = mm;
	tsk->active_mm = mm;
	return 0;

fail_nomem:
	return retval;
}

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static struct fs_struct *__copy_fs_struct(struct fs_struct *old)
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{
	struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
	/* We don't need to lock fs - think why ;-) */
	if (fs) {
		atomic_set(&fs->count, 1);
		rwlock_init(&fs->lock);
		fs->umask = old->umask;
		read_lock(&old->lock);
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		fs->root = old->root;
		path_get(&old->root);
		fs->pwd = old->pwd;
		path_get(&old->pwd);
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		read_unlock(&old->lock);
	}
	return fs;
}

struct fs_struct *copy_fs_struct(struct fs_struct *old)
{
	return __copy_fs_struct(old);
}

EXPORT_SYMBOL_GPL(copy_fs_struct);

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static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
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{
	if (clone_flags & CLONE_FS) {
		atomic_inc(&current->fs->count);
		return 0;
	}
	tsk->fs = __copy_fs_struct(current->fs);
	if (!tsk->fs)
		return -ENOMEM;
	return 0;
}

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static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
{
	struct files_struct *oldf, *newf;
	int error = 0;

	/*
	 * A background process may not have any files ...
	 */
	oldf = current->files;
	if (!oldf)
		goto out;

	if (clone_flags & CLONE_FILES) {
		atomic_inc(&oldf->count);
		goto out;
	}

	newf = dup_fd(oldf, &error);
	if (!newf)
		goto out;

	tsk->files = newf;
	error = 0;
out:
	return error;
}

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static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
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{
#ifdef CONFIG_BLOCK
	struct io_context *ioc = current->io_context;

	if (!ioc)
		return 0;
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	/*
	 * Share io context with parent, if CLONE_IO is set
	 */
	if (clone_flags & CLONE_IO) {
		tsk->io_context = ioc_task_link(ioc);
		if (unlikely(!tsk->io_context))
			return -ENOMEM;
	} else if (ioprio_valid(ioc->ioprio)) {
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		tsk->io_context = alloc_io_context(GFP_KERNEL, -1);
		if (unlikely(!tsk->io_context))
			return -ENOMEM;

		tsk->io_context->ioprio = ioc->ioprio;
	}
#endif
	return 0;
}

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static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
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{
	struct sighand_struct *sig;

	if (clone_flags & (CLONE_SIGHAND | CLONE_THREAD)) {
		atomic_inc(&current->sighand->count);
		return 0;
	}
	sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
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	rcu_assign_pointer(tsk->sighand, sig);
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	if (!sig)
		return -ENOMEM;
	atomic_set(&sig->count, 1);
	memcpy(sig->action, current->sighand->action, sizeof(sig->action));
	return 0;
}

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void __cleanup_sighand(struct sighand_struct *sighand)
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{
	if (atomic_dec_and_test(&sighand->count))
		kmem_cache_free(sighand_cachep, sighand);
}

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static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
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{
	struct signal_struct *sig;
	int ret;

	if (clone_flags & CLONE_THREAD) {
		atomic_inc(&current->signal->count);
		atomic_inc(&current->signal->live);
		return 0;
	}
	sig = kmem_cache_alloc(signal_cachep, GFP_KERNEL);
	tsk->signal = sig;
	if (!sig)
		return -ENOMEM;

	ret = copy_thread_group_keys(tsk);
	if (ret < 0) {
		kmem_cache_free(signal_cachep, sig);
		return ret;
	}

	atomic_set(&sig->count, 1);
	atomic_set(&sig->live, 1);
	init_waitqueue_head(&sig->wait_chldexit);
	sig->flags = 0;
	sig->group_exit_code = 0;
	sig->group_exit_task = NULL;
	sig->group_stop_count = 0;
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	sig->curr_target = tsk;
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	init_sigpending(&sig->shared_pending);
	INIT_LIST_HEAD(&sig->posix_timers);

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	hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
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	sig->it_real_incr.tv64 = 0;
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	sig->real_timer.function = it_real_fn;

	sig->it_virt_expires = cputime_zero;
	sig->it_virt_incr = cputime_zero;
	sig->it_prof_expires = cputime_zero;
	sig->it_prof_incr = cputime_zero;

	sig->leader = 0;	/* session leadership doesn't inherit */
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	sig->tty_old_pgrp = NULL;
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	sig->tty = NULL;
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	sig->utime = sig->stime = sig->cutime = sig->cstime = cputime_zero;
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	sig->gtime = cputime_zero;
	sig->cgtime = cputime_zero;
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	sig->nvcsw = sig->nivcsw = sig->cnvcsw = sig->cnivcsw = 0;
	sig->min_flt = sig->maj_flt = sig->cmin_flt = sig->cmaj_flt = 0;
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	sig->inblock = sig->oublock = sig->cinblock = sig->coublock = 0;
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	task_io_accounting_init(&sig->ioac);
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	sig->sum_sched_runtime = 0;
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	INIT_LIST_HEAD(&sig->cpu_timers[0]);
	INIT_LIST_HEAD(&sig->cpu_timers[1]);
	INIT_LIST_HEAD(&sig->cpu_timers[2]);
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	taskstats_tgid_init(sig);
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	task_lock(current->group_leader);
	memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
	task_unlock(current->group_leader);

	if (sig->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY) {
		/*
		 * New sole thread in the process gets an expiry time
		 * of the whole CPU time limit.
		 */
		tsk->it_prof_expires =
			secs_to_cputime(sig->rlim[RLIMIT_CPU].rlim_cur);
	}
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	acct_init_pacct(&sig->pacct);
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	tty_audit_fork(sig);

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	return 0;
}

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void __cleanup_signal(struct signal_struct *sig)
{
	exit_thread_group_keys(sig);
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	tty_kref_put(sig->tty);
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	kmem_cache_free(signal_cachep, sig);
}

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static void cleanup_signal(struct task_struct *tsk)
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{
	struct signal_struct *sig = tsk->signal;

	atomic_dec(&sig->live);

	if (atomic_dec_and_test(&sig->count))
		__cleanup_signal(sig);
}

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static void copy_flags(unsigned long clone_flags, struct task_struct *p)
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{
	unsigned long new_flags = p->flags;

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	new_flags &= ~PF_SUPERPRIV;
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	new_flags |= PF_FORKNOEXEC;
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	new_flags |= PF_STARTING;
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	p->flags = new_flags;
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	clear_freeze_flag(p);
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}

asmlinkage long sys_set_tid_address(int __user *tidptr)
{
	current->clear_child_tid = tidptr;

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	return task_pid_vnr(current);
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}

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static void rt_mutex_init_task(struct task_struct *p)
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{
	spin_lock_init(&p->pi_lock);
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#ifdef CONFIG_RT_MUTEXES
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	plist_head_init(&p->pi_waiters, &p->pi_lock);
	p->pi_blocked_on = NULL;
#endif
}

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#ifdef CONFIG_MM_OWNER
void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
{
	mm->owner = p;
}
#endif /* CONFIG_MM_OWNER */

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/*
 * This creates a new process as a copy of the old one,
 * but does not actually start it yet.
 *
 * It copies the registers, and all the appropriate
 * parts of the process environment (as per the clone
 * flags). The actual kick-off is left to the caller.
 */
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static struct task_struct *copy_process(unsigned long clone_flags,
					unsigned long stack_start,
					struct pt_regs *regs,
					unsigned long stack_size,
					int __user *child_tidptr,
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					struct pid *pid,
					int trace)
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{
	int retval;
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	struct task_struct *p;
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	int cgroup_callbacks_done = 0;
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	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
		return ERR_PTR(-EINVAL);

	/*
	 * Thread groups must share signals as well, and detached threads
	 * can only be started up within the thread group.
	 */
	if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
		return ERR_PTR(-EINVAL);

	/*
	 * Shared signal handlers imply shared VM. By way of the above,
	 * thread groups also imply shared VM. Blocking this case allows
	 * for various simplifications in other code.
	 */
	if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
		return ERR_PTR(-EINVAL);

	retval = security_task_create(clone_flags);
	if (retval)
		goto fork_out;

	retval = -ENOMEM;
	p = dup_task_struct(current);
	if (!p)
		goto fork_out;

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	rt_mutex_init_task(p);

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#ifdef CONFIG_PROVE_LOCKING
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	DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
#endif
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	retval = -EAGAIN;
	if (atomic_read(&p->user->processes) >=
			p->signal->rlim[RLIMIT_NPROC].rlim_cur) {
		if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
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		    p->user != current->nsproxy->user_ns->root_user)
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			goto bad_fork_free;
	}

	atomic_inc(&p->user->__count);
	atomic_inc(&p->user->processes);
	get_group_info(p->group_info);

	/*
	 * If multiple threads are within copy_process(), then this check
	 * triggers too late. This doesn't hurt, the check is only there
	 * to stop root fork bombs.
	 */
	if (nr_threads >= max_threads)
		goto bad_fork_cleanup_count;

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	if (!try_module_get(task_thread_info(p)->exec_domain->module))
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		goto bad_fork_cleanup_count;

	if (p->binfmt && !try_module_get(p->binfmt->module))
		goto bad_fork_cleanup_put_domain;

	p->did_exec = 0;
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	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */
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	copy_flags(clone_flags, p);
	INIT_LIST_HEAD(&p->children);
	INIT_LIST_HEAD(&p->sibling);
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#ifdef CONFIG_PREEMPT_RCU
	p->rcu_read_lock_nesting = 0;
	p->rcu_flipctr_idx = 0;
#endif /* #ifdef CONFIG_PREEMPT_RCU */
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	p->vfork_done = NULL;
	spin_lock_init(&p->alloc_lock);

	clear_tsk_thread_flag(p, TIF_SIGPENDING);
	init_sigpending(&p->pending);

	p->utime = cputime_zero;
	p->stime = cputime_zero;
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	p->gtime = cputime_zero;
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	p->utimescaled = cputime_zero;
	p->stimescaled = cputime_zero;
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	p->prev_utime = cputime_zero;
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	p->prev_stime = cputime_zero;
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#ifdef CONFIG_DETECT_SOFTLOCKUP
	p->last_switch_count = 0;
	p->last_switch_timestamp = 0;
#endif

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	task_io_accounting_init(&p->ioac);
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	acct_clear_integrals(p);

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	p->it_virt_expires = cputime_zero;
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	p->it_prof_expires = cputime_zero;
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	p->it_sched_expires = 0;
	INIT_LIST_HEAD(&p->cpu_timers[0]);
	INIT_LIST_HEAD(&p->cpu_timers[1]);
	INIT_LIST_HEAD(&p->cpu_timers[2]);
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	p->lock_depth = -1;		/* -1 = no lock */
	do_posix_clock_monotonic_gettime(&p->start_time);
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	p->real_start_time = p->start_time;
	monotonic_to_bootbased(&p->real_start_time);
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#ifdef CONFIG_SECURITY
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	p->security = NULL;
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#endif
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	p->cap_bset = current->cap_bset;
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	p->io_context = NULL;
	p->audit_context = NULL;
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	cgroup_fork(p);
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#ifdef CONFIG_NUMA
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	p->mempolicy = mpol_dup(p->mempolicy);
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 	if (IS_ERR(p->mempolicy)) {
 		retval = PTR_ERR(p->mempolicy);
 		p->mempolicy = NULL;
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 		goto bad_fork_cleanup_cgroup;
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 	}
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	mpol_fix_fork_child_flag(p);
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#endif
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#ifdef CONFIG_TRACE_IRQFLAGS
	p->irq_events = 0;
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#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
	p->hardirqs_enabled = 1;
#else
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	p->hardirqs_enabled = 0;
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#endif
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	p->hardirq_enable_ip = 0;
	p->hardirq_enable_event = 0;
	p->hardirq_disable_ip = _THIS_IP_;
	p->hardirq_disable_event = 0;
	p->softirqs_enabled = 1;
	p->softirq_enable_ip = _THIS_IP_;
	p->softirq_enable_event = 0;
	p->softirq_disable_ip = 0;
	p->softirq_disable_event = 0;
	p->hardirq_context = 0;
	p->softirq_context = 0;
#endif
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#ifdef CONFIG_LOCKDEP
	p->lockdep_depth = 0; /* no locks held yet */
	p->curr_chain_key = 0;
	p->lockdep_recursion = 0;
#endif
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#ifdef CONFIG_DEBUG_MUTEXES
	p->blocked_on = NULL; /* not blocked yet */
#endif

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	/* Perform scheduler related setup. Assign this task to a CPU. */
	sched_fork(p, clone_flags);

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	if ((retval = security_task_alloc(p)))
		goto bad_fork_cleanup_policy;
	if ((retval = audit_alloc(p)))
		goto bad_fork_cleanup_security;
	/* copy all the process information */
	if ((retval = copy_semundo(clone_flags, p)))
		goto bad_fork_cleanup_audit;
	if ((retval = copy_files(clone_flags, p)))
		goto bad_fork_cleanup_semundo;
	if ((retval = copy_fs(clone_flags, p)))
		goto bad_fork_cleanup_files;
	if ((retval = copy_sighand(clone_flags, p)))
		goto bad_fork_cleanup_fs;
	if ((retval = copy_signal(clone_flags, p)))
		goto bad_fork_cleanup_sighand;
	if ((retval = copy_mm(clone_flags, p)))
		goto bad_fork_cleanup_signal;
	if ((retval = copy_keys(clone_flags, p)))
		goto bad_fork_cleanup_mm;
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	if ((retval = copy_namespaces(clone_flags, p)))
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		goto bad_fork_cleanup_keys;
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	if ((retval = copy_io(clone_flags, p)))
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		goto bad_fork_cleanup_namespaces;
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	retval = copy_thread(0, clone_flags, stack_start, stack_size, p, regs);
	if (retval)
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		goto bad_fork_cleanup_io;
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	if (pid != &init_struct_pid) {
		retval = -ENOMEM;
		pid = alloc_pid(task_active_pid_ns(p));
		if (!pid)
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			goto bad_fork_cleanup_io;
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		if (clone_flags & CLONE_NEWPID) {
			retval = pid_ns_prepare_proc(task_active_pid_ns(p));
			if (retval < 0)
				goto bad_fork_free_pid;
		}
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	}

	p->pid = pid_nr(pid);
	p->tgid = p->pid;
	if (clone_flags & CLONE_THREAD)
		p->tgid = current->tgid;

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	if (current->nsproxy != p->nsproxy) {
		retval = ns_cgroup_clone(p, pid);
		if (retval)
			goto bad_fork_free_pid;
	}

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	p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
	/*
	 * Clear TID on mm_release()?
	 */
	p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr: NULL;
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#ifdef CONFIG_FUTEX
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	p->robust_list = NULL;
#ifdef CONFIG_COMPAT
	p->compat_robust_list = NULL;
#endif
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	INIT_LIST_HEAD(&p->pi_state_list);
	p->pi_state_cache = NULL;
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#endif
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	/*
	 * sigaltstack should be cleared when sharing the same VM
	 */
	if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
		p->sas_ss_sp = p->sas_ss_size = 0;

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	/*
	 * Syscall tracing should be turned off in the child regardless
	 * of CLONE_PTRACE.
	 */
	clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
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#ifdef TIF_SYSCALL_EMU
	clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
#endif
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	clear_all_latency_tracing(p);
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	/* Our parent execution domain becomes current domain
	   These must match for thread signalling to apply */
	p->parent_exec_id = p->self_exec_id;

	/* ok, now we should be set up.. */
	p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
	p->pdeath_signal = 0;
	p->exit_state = 0;

	/*
	 * Ok, make it visible to the rest of the system.
	 * We dont wake it up yet.
	 */
	p->group_leader = p;
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	INIT_LIST_HEAD(&p->thread_group);
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	/* Now that the task is set up, run cgroup callbacks if
	 * necessary. We need to run them before the task is visible
	 * on the tasklist. */
	cgroup_fork_callbacks(p);
	cgroup_callbacks_done = 1;

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	/* Need tasklist lock for parent etc handling! */
	write_lock_irq(&tasklist_lock);

	/*
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	 * The task hasn't been attached yet, so its cpus_allowed mask will
	 * not be changed, nor will its assigned CPU.
	 *
	 * The cpus_allowed mask of the parent may have changed after it was
	 * copied first time - so re-copy it here, then check the child's CPU
	 * to ensure it is on a valid CPU (and if not, just force it back to
	 * parent's CPU). This avoids alot of nasty races.
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	 */
	p->cpus_allowed = current->cpus_allowed;
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	p->rt.nr_cpus_allowed = current->rt.nr_cpus_allowed;
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	if (unlikely(!cpu_isset(task_cpu(p), p->cpus_allowed) ||
			!cpu_online(task_cpu(p))))
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		set_task_cpu(p, smp_processor_id());
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	/* CLONE_PARENT re-uses the old parent */
	if (clone_flags & (CLONE_PARENT|CLONE_THREAD))
		p->real_parent = current->real_parent;
	else
		p->real_parent = current;

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	spin_lock(&current->sighand->siglock);
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	/*
	 * Process group and session signals need to be delivered to just the
	 * parent before the fork or both the parent and the child after the
	 * fork. Restart if a signal comes in before we add the new process to
	 * it's process group.
	 * A fatal signal pending means that current will exit, so the new
	 * thread can't slip out of an OOM kill (or normal SIGKILL).
 	 */
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	recalc_sigpending();
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	if (signal_pending(current)) {
		spin_unlock(&current->sighand->siglock);
		write_unlock_irq(&tasklist_lock);
		retval = -ERESTARTNOINTR;
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		goto bad_fork_free_pid;
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	}

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	if (clone_flags & CLONE_THREAD) {
		p->group_leader = current->group_leader;
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		list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group);
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		if (!cputime_eq(current->signal->it_virt_expires,
				cputime_zero) ||
		    !cputime_eq(current->signal->it_prof_expires,
				cputime_zero) ||
		    current->signal->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY ||
		    !list_empty(&current->signal->cpu_timers[0]) ||
		    !list_empty(&current->signal->cpu_timers[1]) ||
		    !list_empty(&current->signal->cpu_timers[2])) {
			/*
			 * Have child wake up on its first tick to check
			 * for process CPU timers.
			 */
			p->it_prof_expires = jiffies_to_cputime(1);
		}
	}

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	if (likely(p->pid)) {
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		list_add_tail(&p->sibling, &p->real_parent->children);
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		tracehook_finish_clone(p, clone_flags, trace);
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		if (thread_group_leader(p)) {
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			if (clone_flags & CLONE_NEWPID)
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				p->nsproxy->pid_ns->child_reaper = p;
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			p->signal->leader_pid = pid;
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			tty_kref_put(p->signal->tty);
			p->signal->tty = tty_kref_get(current->signal->tty);
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			set_task_pgrp(p, task_pgrp_nr(current));
			set_task_session(p, task_session_nr(current));
			attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
			attach_pid(p, PIDTYPE_SID, task_session(current));
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			list_add_tail_rcu(&p->tasks, &init_task.tasks);
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			__get_cpu_var(process_counts)++;
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		}
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		attach_pid(p, PIDTYPE_PID, pid);
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		nr_threads++;
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	}

	total_forks++;
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	spin_unlock(&current->sighand->siglock);
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	write_unlock_irq(&tasklist_lock);
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	proc_fork_connector(p);
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	cgroup_post_fork(p);
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	return p;

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bad_fork_free_pid:
	if (pid != &init_struct_pid)
		free_pid(pid);
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bad_fork_cleanup_io:
	put_io_context(p->io_context);
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bad_fork_cleanup_namespaces:
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	exit_task_namespaces(p);
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bad_fork_cleanup_keys:
	exit_keys(p);
bad_fork_cleanup_mm:
	if (p->mm)
		mmput(p->mm);
bad_fork_cleanup_signal:
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	cleanup_signal(p);
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bad_fork_cleanup_sighand:
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	__cleanup_sighand(p->sighand);
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bad_fork_cleanup_fs:
	exit_fs(p); /* blocking */
bad_fork_cleanup_files:
	exit_files(p); /* blocking */
bad_fork_cleanup_semundo:
	exit_sem(p);
bad_fork_cleanup_audit:
	audit_free(p);
bad_fork_cleanup_security:
	security_task_free(p);
bad_fork_cleanup_policy:
#ifdef CONFIG_NUMA
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	mpol_put(p->mempolicy);
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bad_fork_cleanup_cgroup:
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#endif
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	cgroup_exit(p, cgroup_callbacks_done);
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	delayacct_tsk_free(p);
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	if (p->binfmt)
		module_put(p->binfmt->module);
bad_fork_cleanup_put_domain:
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	module_put(task_thread_info(p)->exec_domain->module);
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bad_fork_cleanup_count:
	put_group_info(p->group_info);
	atomic_dec(&p->user->processes);
	free_uid(p->user);
bad_fork_free:
	free_task(p);
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fork_out:
	return ERR_PTR(retval);
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}

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noinline struct pt_regs * __cpuinit __attribute__((weak)) idle_regs(struct pt_regs *regs)
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{
	memset(regs, 0, sizeof(struct pt_regs));
	return regs;
}

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struct task_struct * __cpuinit fork_idle(int cpu)
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{
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	struct task_struct *task;
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	struct pt_regs regs;

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	task = copy_process(CLONE_VM, 0, idle_regs(&regs), 0, NULL,
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			    &init_struct_pid, 0);
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	if (!IS_ERR(task))
		init_idle(task, cpu);
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	return task;
}

/*
 *  Ok, this is the main fork-routine.
 *
 * It copies the process, and if successful kick-starts
 * it and waits for it to finish using the VM if required.
 */
long do_fork(unsigned long clone_flags,
	      unsigned long stack_start,
	      struct pt_regs *regs,
	      unsigned long stack_size,
	      int __user *parent_tidptr,
	      int __user *child_tidptr)
{
	struct task_struct *p;
	int trace = 0;
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	long nr;
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	/*
	 * We hope to recycle these flags after 2.6.26
	 */
	if (unlikely(clone_flags & CLONE_STOPPED)) {
		static int __read_mostly count = 100;

		if (count > 0 && printk_ratelimit()) {
			char comm[TASK_COMM_LEN];

			count--;
			printk(KERN_INFO "fork(): process `%s' used deprecated "
					"clone flags 0x%lx\n",
				get_task_comm(comm, current),
				clone_flags & CLONE_STOPPED);
		}
	}

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	/*
	 * When called from kernel_thread, don't do user tracing stuff.
	 */
	if (likely(user_mode(regs)))
		trace = tracehook_prepare_clone(clone_flags);
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	p = copy_process(clone_flags, stack_start, regs, stack_size,
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			 child_tidptr, NULL, trace);
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	/*
	 * Do this prior waking up the new thread - the thread pointer
	 * might get invalid after that point, if the thread exits quickly.
	 */
	if (!IS_ERR(p)) {
		struct completion vfork;

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		nr = task_pid_vnr(p);
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		if (clone_flags & CLONE_PARENT_SETTID)
			put_user(nr, parent_tidptr);
1371

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		if (clone_flags & CLONE_VFORK) {
			p->vfork_done = &vfork;
			init_completion(&vfork);
		}

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		tracehook_report_clone(trace, regs, clone_flags, nr, p);

		/*
		 * We set PF_STARTING at creation in case tracing wants to
		 * use this to distinguish a fully live task from one that
		 * hasn't gotten to tracehook_report_clone() yet.  Now we
		 * clear it and set the child going.
		 */
		p->flags &= ~PF_STARTING;

		if (unlikely(clone_flags & CLONE_STOPPED)) {
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			/*
			 * We'll start up with an immediate SIGSTOP.
			 */
			sigaddset(&p->pending.signal, SIGSTOP);
			set_tsk_thread_flag(p, TIF_SIGPENDING);
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			__set_task_state(p, TASK_STOPPED);
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		} else {
			wake_up_new_task(p, clone_flags);
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		}

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		tracehook_report_clone_complete(trace, regs,
						clone_flags, nr, p);

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		if (clone_flags & CLONE_VFORK) {
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			freezer_do_not_count();
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			wait_for_completion(&vfork);
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			freezer_count();
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			tracehook_report_vfork_done(p, nr);
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		}
	} else {
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		nr = PTR_ERR(p);
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	}
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	return nr;
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}

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#ifndef ARCH_MIN_MMSTRUCT_ALIGN
#define ARCH_MIN_MMSTRUCT_ALIGN 0
#endif

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static void sighand_ctor(void *data)
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{
	struct sighand_struct *sighand = data;

1421
	spin_lock_init(&sighand->siglock);
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	init_waitqueue_head(&sighand->signalfd_wqh);
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}

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void __init proc_caches_init(void)
{
	sighand_cachep = kmem_cache_create("sighand_cache",
			sizeof(struct sighand_struct), 0,
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			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU,
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			sighand_ctor);
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	signal_cachep = kmem_cache_create("signal_cache",
			sizeof(struct signal_struct), 0,
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			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
	files_cachep = kmem_cache_create("files_cache",
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			sizeof(struct files_struct), 0,
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			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
	fs_cachep = kmem_cache_create("fs_cache",
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			sizeof(struct fs_struct), 0,
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			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
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	vm_area_cachep = kmem_cache_create("vm_area_struct",
			sizeof(struct vm_area_struct), 0,
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			SLAB_PANIC, NULL);
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	mm_cachep = kmem_cache_create("mm_struct",
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			sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
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			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
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}
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/*
 * Check constraints on flags passed to the unshare system call and
 * force unsharing of additional process context as appropriate.
 */
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static void check_unshare_flags(unsigned long *flags_ptr)
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