fork.c 46.9 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>
#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/seccomp.h>
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#include <linux/swap.h>
#include <linux/syscalls.h>
#include <linux/jiffies.h>
#include <linux/futex.h>
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#include <linux/compat.h>
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#include <linux/kthread.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/ftrace.h>
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#include <linux/proc_fs.h>
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#include <linux/profile.h>
#include <linux/rmap.h>
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#include <linux/ksm.h>
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#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/blkdev.h>
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#include <linux/fs_struct.h>
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#include <linux/magic.h>
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#include <linux/perf_event.h>
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#include <linux/posix-timers.h>
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#include <linux/user-return-notifier.h>
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#include <linux/oom.h>
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#include <linux/khugepaged.h>
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#include <linux/signalfd.h>
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#include <linux/uprobes.h>
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#include <linux/aio.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>

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#include <trace/events/sched.h>

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#define CREATE_TRACE_POINTS
#include <trace/events/task.h>

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/*
 * Protected counters by write_lock_irq(&tasklist_lock)
 */
unsigned long total_forks;	/* Handle normal Linux uptimes. */
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int nr_threads;			/* The idle threads do not count.. */
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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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#ifdef CONFIG_PROVE_RCU
int lockdep_tasklist_lock_is_held(void)
{
	return lockdep_is_held(&tasklist_lock);
}
EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
#endif /* #ifdef CONFIG_PROVE_RCU */
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int nr_processes(void)
{
	int cpu;
	int total = 0;

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

	return total;
}

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void __weak arch_release_task_struct(struct task_struct *tsk)
{
}

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#ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
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static struct kmem_cache *task_struct_cachep;
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static inline struct task_struct *alloc_task_struct_node(int node)
{
	return kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL, node);
}

static inline void free_task_struct(struct task_struct *tsk)
{
	kmem_cache_free(task_struct_cachep, tsk);
}
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#endif

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void __weak arch_release_thread_info(struct thread_info *ti)
{
}

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#ifndef CONFIG_ARCH_THREAD_INFO_ALLOCATOR
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/*
 * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
 * kmemcache based allocator.
 */
# if THREAD_SIZE >= PAGE_SIZE
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static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
						  int node)
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{
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	struct page *page = alloc_pages_node(node, THREADINFO_GFP_ACCOUNTED,
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					     THREAD_SIZE_ORDER);
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	return page ? page_address(page) : NULL;
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}

static inline void free_thread_info(struct thread_info *ti)
{
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	free_memcg_kmem_pages((unsigned long)ti, THREAD_SIZE_ORDER);
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}
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# else
static struct kmem_cache *thread_info_cache;

static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
						  int node)
{
	return kmem_cache_alloc_node(thread_info_cache, THREADINFO_GFP, node);
}

static void free_thread_info(struct thread_info *ti)
{
	kmem_cache_free(thread_info_cache, ti);
}

void thread_info_cache_init(void)
{
	thread_info_cache = kmem_cache_create("thread_info", THREAD_SIZE,
					      THREAD_SIZE, 0, NULL);
	BUG_ON(thread_info_cache == NULL);
}
# endif
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#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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/* Notifier list called when a task struct is freed */
static ATOMIC_NOTIFIER_HEAD(task_free_notifier);

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static void account_kernel_stack(struct thread_info *ti, int account)
{
	struct zone *zone = page_zone(virt_to_page(ti));

	mod_zone_page_state(zone, NR_KERNEL_STACK, account);
}

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void free_task(struct task_struct *tsk)
{
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	account_kernel_stack(tsk->stack, -1);
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	arch_release_thread_info(tsk->stack);
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	free_thread_info(tsk->stack);
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	rt_mutex_debug_task_free(tsk);
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	ftrace_graph_exit_task(tsk);
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	put_seccomp_filter(tsk);
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	arch_release_task_struct(tsk);
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	free_task_struct(tsk);
}
EXPORT_SYMBOL(free_task);

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static inline void free_signal_struct(struct signal_struct *sig)
{
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	taskstats_tgid_free(sig);
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	sched_autogroup_exit(sig);
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	kmem_cache_free(signal_cachep, sig);
}

static inline void put_signal_struct(struct signal_struct *sig)
{
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	if (atomic_dec_and_test(&sig->sigcnt))
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		free_signal_struct(sig);
}

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int task_free_register(struct notifier_block *n)
{
	return atomic_notifier_chain_register(&task_free_notifier, n);
}
EXPORT_SYMBOL(task_free_register);

int task_free_unregister(struct notifier_block *n)
{
	return atomic_notifier_chain_unregister(&task_free_notifier, n);
}
EXPORT_SYMBOL(task_free_unregister);

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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);

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	security_task_free(tsk);
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	exit_creds(tsk);
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	delayacct_tsk_free(tsk);
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	put_signal_struct(tsk->signal);
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	atomic_notifier_call_chain(&task_free_notifier, 0, tsk);
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	if (!profile_handoff_task(tsk))
		free_task(tsk);
}
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EXPORT_SYMBOL_GPL(__put_task_struct);
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void __init __weak arch_task_cache_init(void) { }
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void __init fork_init(unsigned long mempages)
{
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#ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
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#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 | SLAB_NOTRACK, 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
	 */
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	if (max_threads < 20)
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		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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	unsigned long *stackend;
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	int node = tsk_fork_get_node(orig);
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	int err;
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	tsk = alloc_task_struct_node(node);
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	if (!tsk)
		return NULL;

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	ti = alloc_thread_info_node(tsk, node);
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	if (!ti)
		goto free_tsk;
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	err = arch_dup_task_struct(tsk, orig);
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	if (err)
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		goto free_ti;
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	tsk->stack = ti;

	setup_thread_stack(tsk, orig);
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	clear_user_return_notifier(tsk);
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	clear_tsk_need_resched(tsk);
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	stackend = end_of_stack(tsk);
	*stackend = STACK_END_MAGIC;	/* for overflow detection */
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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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#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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	tsk->task_frag.page = NULL;
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	account_kernel_stack(ti, 1);

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	return tsk;
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free_ti:
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	free_thread_info(ti);
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free_tsk:
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	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, *prev, **pprev;
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	struct rb_node **rb_link, *rb_parent;
	int retval;
	unsigned long charge;
	struct mempolicy *pol;

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	uprobe_start_dup_mmap();
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	down_write(&oldmm->mmap_sem);
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	flush_cache_dup_mm(oldmm);
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	uprobe_dup_mmap(oldmm, mm);
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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;
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	cpumask_clear(mm_cpumask(mm));
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	mm->mm_rb = RB_ROOT;
	rb_link = &mm->mm_rb.rb_node;
	rb_parent = NULL;
	pprev = &mm->mmap;
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	retval = ksm_fork(mm, oldmm);
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	if (retval)
		goto out;
	retval = khugepaged_fork(mm, oldmm);
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	if (retval)
		goto out;
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	prev = NULL;
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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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			vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
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							-vma_pages(mpnt));
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			continue;
		}
		charge = 0;
		if (mpnt->vm_flags & VM_ACCOUNT) {
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			unsigned long len = vma_pages(mpnt);

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			if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
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				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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		INIT_LIST_HEAD(&tmp->anon_vma_chain);
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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);
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		tmp->vm_mm = mm;
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		if (anon_vma_fork(tmp, mpnt))
			goto fail_nomem_anon_vma_fork;
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		tmp->vm_flags &= ~VM_LOCKED;
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		tmp->vm_next = tmp->vm_prev = NULL;
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		file = tmp->vm_file;
		if (file) {
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			struct inode *inode = file_inode(file);
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			struct address_space *mapping = file->f_mapping;

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			vma_get_file(tmp);
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			if (tmp->vm_flags & VM_DENYWRITE)
				atomic_dec(&inode->i_writecount);
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			mutex_lock(&mapping->i_mmap_mutex);
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			if (tmp->vm_flags & VM_SHARED)
				mapping->i_mmap_writable++;
			flush_dcache_mmap_lock(mapping);
			/* insert tmp into the share list, just after mpnt */
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			if (unlikely(tmp->vm_flags & VM_NONLINEAR))
				vma_nonlinear_insert(tmp,
						&mapping->i_mmap_nonlinear);
			else
				vma_interval_tree_insert_after(tmp, mpnt,
							&mapping->i_mmap);
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			flush_dcache_mmap_unlock(mapping);
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			mutex_unlock(&mapping->i_mmap_mutex);
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		}

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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;
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		tmp->vm_prev = prev;
		prev = tmp;
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		__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);
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	uprobe_end_dup_mmap();
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	return retval;
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fail_nomem_anon_vma_fork:
	mpol_put(pol);
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fail_nomem_policy:
	kmem_cache_free(vm_area_cachep, tmp);
fail_nomem:
	retval = -ENOMEM;
	vm_unacct_memory(charge);
	goto out;
}

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

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static inline void mm_free_pgd(struct mm_struct *mm)
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{
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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)))

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static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;

static int __init coredump_filter_setup(char *s)
{
	default_dump_filter =
		(simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
		MMF_DUMP_FILTER_MASK;
	return 1;
}

__setup("coredump_filter=", coredump_filter_setup);

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#include <linux/init_task.h>

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static void mm_init_aio(struct mm_struct *mm)
{
#ifdef CONFIG_AIO
	spin_lock_init(&mm->ioctx_lock);
	INIT_HLIST_HEAD(&mm->ioctx_list);
#endif
}

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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_INIT_MASK) : default_dump_filter;
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	mm->core_state = NULL;
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	mm->nr_ptes = 0;
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	memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
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	spin_lock_init(&mm->page_table_lock);
	mm->free_area_cache = TASK_UNMAPPED_BASE;
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	mm->cached_hole_size = ~0UL;
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	mm_init_aio(mm);
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	mm_init_owner(mm, p);
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	clear_tlb_flush_pending(mm);
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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;
}

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static void check_mm(struct mm_struct *mm)
{
	int i;

	for (i = 0; i < NR_MM_COUNTERS; i++) {
		long x = atomic_long_read(&mm->rss_stat.count[i]);

		if (unlikely(x))
			printk(KERN_ALERT "BUG: Bad rss-counter state "
					  "mm:%p idx:%d val:%ld\n", mm, i, x);
	}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	VM_BUG_ON(mm->pmd_huge_pte);
#endif
}

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/*
 * Allocate and initialize an mm_struct.
 */
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struct mm_struct *mm_alloc(void)
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{
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	struct mm_struct *mm;
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	mm = allocate_mm();
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	if (!mm)
		return NULL;

	memset(mm, 0, sizeof(*mm));
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	mm_init_cpumask(mm);
	return mm_init(mm, current);
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}

/*
 * 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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	check_mm(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)) {
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		uprobe_clear_state(mm);
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		exit_aio(mm);
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		ksm_exit(mm);
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		khugepaged_exit(mm); /* must run before exit_mmap */
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		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);
		}
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		if (mm->binfmt)
			module_put(mm->binfmt->module);
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		mmdrop(mm);
	}
}
EXPORT_SYMBOL_GPL(mmput);

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void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
{
	if (new_exe_file)
		get_file(new_exe_file);
	if (mm->exe_file)
		fput(mm->exe_file);
	mm->exe_file = new_exe_file;
}

struct file *get_mm_exe_file(struct mm_struct *mm)
{
	struct file *exe_file;

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	/* We need mmap_sem to protect against races with removal of exe_file */
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	down_read(&mm->mmap_sem);
	exe_file = mm->exe_file;
	if (exe_file)
		get_file(exe_file);
	up_read(&mm->mmap_sem);
	return exe_file;
}

static void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
{
	/* It's safe to write the exe_file pointer without exe_file_lock because
	 * this is called during fork when the task is not yet in /proc */
	newmm->exe_file = get_mm_exe_file(oldmm);
}

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/**
 * 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) {
695
		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);

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struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
{
	struct mm_struct *mm;
	int err;

	err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
	if (err)
		return ERR_PTR(err);

	mm = get_task_mm(task);
	if (mm && mm != current->mm &&
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			!ptrace_may_access(task, mode) &&
			!capable(CAP_SYS_RESOURCE)) {
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		mmput(mm);
		mm = ERR_PTR(-EACCES);
	}
	mutex_unlock(&task->signal->cred_guard_mutex);

	return mm;
}

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static void complete_vfork_done(struct task_struct *tsk)
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{
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	struct completion *vfork;
729

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	task_lock(tsk);
	vfork = tsk->vfork_done;
	if (likely(vfork)) {
		tsk->vfork_done = NULL;
		complete(vfork);
	}
	task_unlock(tsk);
}

static int wait_for_vfork_done(struct task_struct *child,
				struct completion *vfork)
{
	int killed;

	freezer_do_not_count();
	killed = wait_for_completion_killable(vfork);
	freezer_count();

	if (killed) {
		task_lock(child);
		child->vfork_done = NULL;
		task_unlock(child);
	}

	put_task_struct(child);
	return killed;
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}

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/* 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)
{
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	/* Get rid of any futexes when releasing the mm */
#ifdef CONFIG_FUTEX
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	if (unlikely(tsk->robust_list)) {
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		exit_robust_list(tsk);
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		tsk->robust_list = NULL;
	}
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#ifdef CONFIG_COMPAT
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	if (unlikely(tsk->compat_robust_list)) {
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		compat_exit_robust_list(tsk);
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		tsk->compat_robust_list = NULL;
	}
784
#endif
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	if (unlikely(!list_empty(&tsk->pi_state_list)))
		exit_pi_state_list(tsk);
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#endif

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	uprobe_free_utask(tsk);

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

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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
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	 * trouble, say, a killed vfork parent shouldn't touch this mm.
	 * Userland only wants this done for a sys_exit.
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	 */
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	if (tsk->clear_child_tid) {
		if (!(tsk->flags & PF_SIGNALED) &&
		    atomic_read(&mm->mm_users) > 1) {
			/*
			 * We don't check the error code - if userspace has
			 * not set up a proper pointer then tough luck.
			 */
			put_user(0, tsk->clear_child_tid);
			sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
					1, NULL, NULL, 0);
		}
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		tsk->clear_child_tid = NULL;
	}
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	/*
	 * All done, finally we can wake up parent and return this mm to him.
	 * Also kthread_stop() uses this completion for synchronization.
	 */
	if (tsk->vfork_done)
		complete_vfork_done(tsk);
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}

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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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	mm_init_cpumask(mm);
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#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	mm->pmd_huge_pte = NULL;
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#endif
#ifdef CONFIG_NUMA_BALANCING
	mm->first_nid = NUMA_PTE_SCAN_INIT;
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#endif
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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;

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	if (mm->binfmt && !try_module_get(mm->binfmt->module))
		goto free_pt;

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	return mm;

free_pt:
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	/* don't put binfmt in mmput, we haven't got module yet */
	mm->binfmt = NULL;
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	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)
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{
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	struct mm_struct *mm, *oldmm;
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	int retval;

	tsk->min_flt = tsk->maj_flt = 0;
	tsk->nvcsw = tsk->nivcsw = 0;
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#ifdef CONFIG_DETECT_HUNG_TASK
	tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
#endif
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	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:
	tsk->mm = mm;
	tsk->active_mm = mm;
	return 0;

fail_nomem:
	return retval;
}

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static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
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{
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	struct fs_struct *fs = current->fs;
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	if (clone_flags & CLONE_FS) {
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		/* tsk->fs is already what we want */
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		spin_lock(&fs->lock);
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		if (fs->in_exec) {
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			spin_unlock(&fs->lock);
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			return -EAGAIN;
		}
		fs->users++;
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		spin_unlock(&fs->lock);
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		return 0;
	}
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	tsk->fs = copy_fs_struct(fs);
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	if (!tsk->fs)
		return -ENOMEM;
	return 0;
}

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static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
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{
	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;
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	struct io_context *new_ioc;
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	if (!ioc)
		return 0;
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	/*
	 * Share io context with parent, if CLONE_IO is set
	 */
	if (clone_flags & CLONE_IO) {
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		ioc_task_link(ioc);
		tsk->io_context = ioc;
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	} else if (ioprio_valid(ioc->ioprio)) {
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		new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
		if (unlikely(!new_ioc))
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			return -ENOMEM;

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		new_ioc->ioprio = ioc->ioprio;
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		put_io_context(new_ioc);
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	}
#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;

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	if (clone_flags & CLONE_SIGHAND) {
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		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)
1020
{
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	if (atomic_dec_and_test(&sighand->count)) {
		signalfd_cleanup(sighand);
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		kmem_cache_free(sighand_cachep, sighand);
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	}
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}

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/*
 * Initialize POSIX timer handling for a thread group.
 */
static void posix_cpu_timers_init_group(struct signal_struct *sig)
{
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	unsigned long cpu_limit;

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	/* Thread group counters. */
	thread_group_cputime_init(sig);

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	cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
	if (cpu_limit != RLIM_INFINITY) {
		sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
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		sig->cputimer.running = 1;
	}

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	/* The timer lists. */
	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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static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
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{
	struct signal_struct *sig;

1054
	if (clone_flags & CLONE_THREAD)
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		return 0;

1057
	sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
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	tsk->signal = sig;
	if (!sig)
		return -ENOMEM;

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	sig->nr_threads = 1;
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	atomic_set(&sig->live, 1);
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	atomic_set(&sig->sigcnt, 1);
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	/* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */
	sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node);
	tsk->thread_node = (struct list_head)LIST_HEAD_INIT(sig->thread_head);

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	init_waitqueue_head(&sig->wait_chldexit);
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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->real_timer.function = it_real_fn;

	task_lock(current->group_leader);
	memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
	task_unlock(current->group_leader);

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	posix_cpu_timers_init_group(sig);

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	tty_audit_fork(sig);
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	sched_autogroup_fork(sig);
1086

1087
#ifdef CONFIG_CGROUPS
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	init_rwsem(&sig->group_rwsem);
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#endif

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	sig->oom_score_adj = current->signal->oom_score_adj;
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	sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1093

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	sig->has_child_subreaper = current->signal->has_child_subreaper ||
				   current->signal->is_child_subreaper;

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	mutex_init(&sig->cred_guard_mutex);

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	return 0;
}

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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 | PF_WQ_WORKER);
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	new_flags |= PF_FORKNOEXEC;
	p->flags = new_flags;
}

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SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
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{
	current->clear_child_tid = tidptr;

1115
	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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{
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	raw_spin_lock_init(&p->pi_lock);
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#ifdef CONFIG_RT_MUTEXES
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	plist_head_init(&p->pi_waiters);
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	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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/*
 * Initialize POSIX timer handling for a single task.
 */
static void posix_cpu_timers_init(struct task_struct *tsk)
{
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	tsk->cputime_expires.prof_exp = 0;
	tsk->cputime_expires.virt_exp = 0;
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	tsk->cputime_expires.sched_exp = 0;
	INIT_LIST_HEAD(&tsk->cpu_timers[0]);
	INIT_LIST_HEAD(&tsk->cpu_timers[1]);
	INIT_LIST_HEAD(&tsk->cpu_timers[2]);
}

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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,
					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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	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
		return ERR_PTR(-EINVAL);

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	if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
		return ERR_PTR(-EINVAL);

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	/*
	 * 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);

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	/*
	 * Siblings of global init remain as zombies on exit since they are
	 * not reaped by their parent (swapper). To solve this and to avoid
	 * multi-rooted process trees, prevent global and container-inits
	 * from creating siblings.
	 */
	if ((clone_flags & CLONE_PARENT) &&
				current->signal->flags & SIGNAL_UNKILLABLE)
		return ERR_PTR(-EINVAL);

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	/*
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	 * If the new process will be in a different pid namespace don't
	 * allow it to share a thread group or signal handlers with the
	 * forking task.
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	 */
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	if ((clone_flags & (CLONE_SIGHAND | CLONE_NEWPID)) &&
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	    (task_active_pid_ns(current) != current->nsproxy->pid_ns))
		return ERR_PTR(-EINVAL);

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	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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	ftrace_graph_init_task(p);
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	get_seccomp_filter(p);
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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;
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	if (atomic_read(&p->real_cred->user->processes) >=
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			task_rlimit(p, RLIMIT_NPROC)) {
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		if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
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		    p->real_cred->user != INIT_USER)
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			goto bad_fork_free;
	}
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	current->flags &= ~PF_NPROC_EXCEEDED;
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	retval = copy_creds(p, clone_flags);
	if (retval < 0)
		goto bad_fork_free;
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	/*
	 * 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.
	 */
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	retval = -EAGAIN;
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	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;

	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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	rcu_copy_process(p);
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	p->vfork_done = NULL;
	spin_lock_init(&p->alloc_lock);

	init_sigpending(&p->pending);

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	p->utime = p->stime = p->gtime = 0;
	p->utimescaled = p->stimescaled = 0;
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#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
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	p->prev_cputime.utime = p->prev_cputime.stime = 0;
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#endif
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#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
	seqlock_init(&p->vtime_seqlock);
	p->vtime_snap = 0;
	p->vtime_snap_whence = VTIME_SLEEPING;
#endif

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#if defined(SPLIT_RSS_COUNTING)
	memset(&p->rss_stat, 0, sizeof(p->rss_stat));
#endif
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	p->default_timer_slack_ns = current->timer_slack_ns;

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

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	posix_cpu_timers_init(p);
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	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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	p->io_context = NULL;
	p->audit_context = NULL;
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	if (clone_flags & CLONE_THREAD)
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		threadgroup_change_begin(current);
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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;
		goto bad_fork_cleanup_cgroup;
	}
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	mpol_fix_fork_child_flag(p);
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#endif
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#ifdef CONFIG_CPUSETS
	p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
	p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
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	seqcount_init(&p->mems_allowed_seq);
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#endif
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#ifdef CONFIG_TRACE_IRQFLAGS
	p->irq_events = 0;
	p->hardirqs_enabled = 0;
	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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#ifdef CONFIG_MEMCG
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	p->memcg_batch.do_batch = 0;
	p->memcg_batch.memcg = NULL;
#endif
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#ifdef CONFIG_BCACHE
	p->sequential_io	= 0;
	p->sequential_io_avg	= 0;
#endif
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	/* Perform scheduler related setup. Assign this task to a CPU. */
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	sched_fork(p);
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	retval = perf_event_init_task(p);
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	if (retval)
		goto bad_fork_cleanup_policy;
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	retval = audit_alloc(p);
	if (retval)
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		goto bad_fork_cleanup_perf;
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	/* copy all the process information */
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	retval = copy_semundo(clone_flags, p);
	if (retval)
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		goto bad_fork_cleanup_audit;