Initial import

1 files changed, 2075 insertions, 0 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
new file mode 100644
index 000000000..e37f372d3
--- /dev/null
+++ b/kernel/fork.c
@@ -0,0 +1,2075 @@
+/*
+ *  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>
+#include <linux/fdtable.h>
+#include <linux/iocontext.h>
+#include <linux/key.h>
+#include <linux/binfmts.h>
+#include <linux/mman.h>
+#include <linux/mmu_notifier.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/vmacache.h>
+#include <linux/nsproxy.h>
+#include <linux/capability.h>
+#include <linux/cpu.h>
+#include <linux/cgroup.h>
+#include <linux/security.h>
+#include <linux/hugetlb.h>
+#include <linux/seccomp.h>
+#include <linux/swap.h>
+#include <linux/syscalls.h>
+#include <linux/jiffies.h>
+#include <linux/futex.h>
+#include <linux/compat.h>
+#include <linux/kthread.h>
+#include <linux/task_io_accounting_ops.h>
+#include <linux/rcupdate.h>
+#include <linux/ptrace.h>
+#include <linux/mount.h>
+#include <linux/audit.h>
+#include <linux/memcontrol.h>
+#include <linux/ftrace.h>
+#include <linux/proc_fs.h>
+#include <linux/profile.h>
+#include <linux/rmap.h>
+#include <linux/ksm.h>
+#include <linux/acct.h>
+#include <linux/tsacct_kern.h>
+#include <linux/cn_proc.h>
+#include <linux/freezer.h>
+#include <linux/delayacct.h>
+#include <linux/taskstats_kern.h>
+#include <linux/random.h>
+#include <linux/tty.h>
+#include <linux/blkdev.h>
+#include <linux/fs_struct.h>
+#include <linux/magic.h>
+#include <linux/perf_event.h>
+#include <linux/posix-timers.h>
+#include <linux/user-return-notifier.h>
+#include <linux/oom.h>
+#include <linux/khugepaged.h>
+#include <linux/signalfd.h>
+#include <linux/uprobes.h>
+#include <linux/aio.h>
+#include <linux/compiler.h>
+#include <linux/sysctl.h>
+
+#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>
+
+#include <trace/events/sched.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/task.h>
+
+/*
+ * Minimum number of threads to boot the kernel
+ */
+#define MIN_THREADS 20
+
+/*
+ * Maximum number of threads
+ */
+#define MAX_THREADS FUTEX_TID_MASK
+
+/*
+ * 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;
+
+__cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
+
+#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 */
+
+int nr_processes(void)
+{
+	int cpu;
+	int total = 0;
+
+	for_each_possible_cpu(cpu)
+		total += per_cpu(process_counts, cpu);
+
+	return total;
+}
+
+void __weak arch_release_task_struct(struct task_struct *tsk)
+{
+}
+
+#ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
+static struct kmem_cache *task_struct_cachep;
+
+static inline struct task_struct *alloc_task_struct_node(int node)
+{
+	return kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL | ___GFP_TOI_NOTRACK, node);
+}
+
+static inline void free_task_struct(struct task_struct *tsk)
+{
+	kmem_cache_free(task_struct_cachep, tsk);
+}
+#endif
+
+void __weak arch_release_thread_info(struct thread_info *ti)
+{
+}
+
+#ifndef CONFIG_ARCH_THREAD_INFO_ALLOCATOR
+
+/*
+ * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
+ * kmemcache based allocator.
+ */
+# if THREAD_SIZE >= PAGE_SIZE
+static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
+						  int node)
+{
+	struct page *page = alloc_kmem_pages_node(node, THREADINFO_GFP,
+						  THREAD_SIZE_ORDER);
+
+	return page ? page_address(page) : NULL;
+}
+
+static inline void free_thread_info(struct thread_info *ti)
+{
+	free_kmem_pages((unsigned long)ti, THREAD_SIZE_ORDER);
+}
+# 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
+#endif
+
+/* SLAB cache for signal_struct structures (tsk->signal) */
+static struct kmem_cache *signal_cachep;
+
+/* SLAB cache for sighand_struct structures (tsk->sighand) */
+struct kmem_cache *sighand_cachep;
+
+/* SLAB cache for files_struct structures (tsk->files) */
+struct kmem_cache *files_cachep;
+
+/* SLAB cache for fs_struct structures (tsk->fs) */
+struct kmem_cache *fs_cachep;
+
+/* SLAB cache for vm_area_struct structures */
+struct kmem_cache *vm_area_cachep;
+
+/* SLAB cache for mm_struct structures (tsk->mm) */
+static struct kmem_cache *mm_cachep;
+
+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);
+}
+
+void free_task(struct task_struct *tsk)
+{
+	account_kernel_stack(tsk->stack, -1);
+	arch_release_thread_info(tsk->stack);
+	free_thread_info(tsk->stack);
+	rt_mutex_debug_task_free(tsk);
+	ftrace_graph_exit_task(tsk);
+	put_seccomp_filter(tsk);
+	arch_release_task_struct(tsk);
+	free_task_struct(tsk);
+}
+EXPORT_SYMBOL(free_task);
+
+static inline void free_signal_struct(struct signal_struct *sig)
+{
+	taskstats_tgid_free(sig);
+	sched_autogroup_exit(sig);
+	kmem_cache_free(signal_cachep, sig);
+}
+
+static inline void put_signal_struct(struct signal_struct *sig)
+{
+	if (atomic_dec_and_test(&sig->sigcnt))
+		free_signal_struct(sig);
+}
+
+void __put_task_struct(struct task_struct *tsk)
+{
+	WARN_ON(!tsk->exit_state);
+	WARN_ON(atomic_read(&tsk->usage));
+	WARN_ON(tsk == current);
+
+	task_numa_free(tsk);
+	security_task_free(tsk);
+	exit_creds(tsk);
+	delayacct_tsk_free(tsk);
+	put_signal_struct(tsk->signal);
+
+	if (!profile_handoff_task(tsk))
+		free_task(tsk);
+}
+EXPORT_SYMBOL_GPL(__put_task_struct);
+
+void __init __weak arch_task_cache_init(void) { }
+
+/*
+ * set_max_threads
+ */
+static void set_max_threads(unsigned int max_threads_suggested)
+{
+	u64 threads;
+
+	/*
+	 * The number of threads shall be limited such that the thread
+	 * structures may only consume a small part of the available memory.
+	 */
+	if (fls64(totalram_pages) + fls64(PAGE_SIZE) > 64)
+		threads = MAX_THREADS;
+	else
+		threads = div64_u64((u64) totalram_pages * (u64) PAGE_SIZE,
+				    (u64) THREAD_SIZE * 8UL);
+
+	if (threads > max_threads_suggested)
+		threads = max_threads_suggested;
+
+	max_threads = clamp_t(u64, threads, MIN_THREADS, MAX_THREADS);
+}
+
+void __init fork_init(void)
+{
+#ifndef CONFIG_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),
+			ARCH_MIN_TASKALIGN, SLAB_PANIC | SLAB_NOTRACK, NULL);
+#endif
+
+	/* do the arch specific task caches init */
+	arch_task_cache_init();
+
+	set_max_threads(MAX_THREADS);
+
+	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];
+}
+
+int __weak arch_dup_task_struct(struct task_struct *dst,
+					       struct task_struct *src)
+{
+	*dst = *src;
+	return 0;
+}
+
+void set_task_stack_end_magic(struct task_struct *tsk)
+{
+	unsigned long *stackend;
+
+	stackend = end_of_stack(tsk);
+	*stackend = STACK_END_MAGIC;	/* for overflow detection */
+}
+
+static struct task_struct *dup_task_struct(struct task_struct *orig)
+{
+	struct task_struct *tsk;
+	struct thread_info *ti;
+	int node = tsk_fork_get_node(orig);
+	int err;
+
+	tsk = alloc_task_struct_node(node);
+	if (!tsk)
+		return NULL;
+
+	ti = alloc_thread_info_node(tsk, node);
+	if (!ti)
+		goto free_tsk;
+
+	err = arch_dup_task_struct(tsk, orig);
+	if (err)
+		goto free_ti;
+
+	tsk->stack = ti;
+#ifdef CONFIG_SECCOMP
+	/*
+	 * We must handle setting up seccomp filters once we're under
+	 * the sighand lock in case orig has changed between now and
+	 * then. Until then, filter must be NULL to avoid messing up
+	 * the usage counts on the error path calling free_task.
+	 */
+	tsk->seccomp.filter = NULL;
+#endif
+
+	setup_thread_stack(tsk, orig);
+	clear_user_return_notifier(tsk);
+	clear_tsk_need_resched(tsk);
+	set_task_stack_end_magic(tsk);
+
+#ifdef CONFIG_CC_STACKPROTECTOR
+	tsk->stack_canary = get_random_int();
+#endif
+
+	/*
+	 * One for us, one for whoever does the "release_task()" (usually
+	 * parent)
+	 */
+	atomic_set(&tsk->usage, 2);
+#ifdef CONFIG_BLK_DEV_IO_TRACE
+	tsk->btrace_seq = 0;
+#endif
+	tsk->splice_pipe = NULL;
+	tsk->task_frag.page = NULL;
+
+	account_kernel_stack(ti, 1);
+
+	return tsk;
+
+free_ti:
+	free_thread_info(ti);
+free_tsk:
+	free_task_struct(tsk);
+	return NULL;
+}
+
+#ifdef CONFIG_MMU
+static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
+{
+	struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
+	struct rb_node **rb_link, *rb_parent;
+	int retval;
+	unsigned long charge;
+
+	uprobe_start_dup_mmap();
+	down_write(&oldmm->mmap_sem);
+	flush_cache_dup_mm(oldmm);
+	uprobe_dup_mmap(oldmm, mm);
+	/*
+	 * Not linked in yet - no deadlock potential:
+	 */
+	down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
+
+	/* No ordering required: file already has been exposed. */
+	RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
+
+	mm->total_vm = oldmm->total_vm;
+	mm->shared_vm = oldmm->shared_vm;
+	mm->exec_vm = oldmm->exec_vm;
+	mm->stack_vm = oldmm->stack_vm;
+
+	rb_link = &mm->mm_rb.rb_node;
+	rb_parent = NULL;
+	pprev = &mm->mmap;
+	retval = ksm_fork(mm, oldmm);
+	if (retval)
+		goto out;
+	retval = khugepaged_fork(mm, oldmm);
+	if (retval)
+		goto out;
+
+	prev = NULL;
+	for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
+		struct file *file;
+
+		if (mpnt->vm_flags & VM_DONTCOPY) {
+			vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
+							-vma_pages(mpnt));
+			continue;
+		}
+		charge = 0;
+		if (mpnt->vm_flags & VM_ACCOUNT) {
+			unsigned long len = vma_pages(mpnt);
+
+			if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
+				goto fail_nomem;
+			charge = len;
+		}
+		tmp = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
+		if (!tmp)
+			goto fail_nomem;
+		*tmp = *mpnt;
+		INIT_LIST_HEAD(&tmp->anon_vma_chain);
+		retval = vma_dup_policy(mpnt, tmp);
+		if (retval)
+			goto fail_nomem_policy;
+		tmp->vm_mm = mm;
+		if (anon_vma_fork(tmp, mpnt))
+			goto fail_nomem_anon_vma_fork;
+		tmp->vm_flags &= ~VM_LOCKED;
+		tmp->vm_next = tmp->vm_prev = NULL;
+		file = tmp->vm_file;
+		if (file) {
+			struct inode *inode = file_inode(file);
+			struct address_space *mapping = file->f_mapping;
+
+			vma_get_file(tmp);
+			if (tmp->vm_flags & VM_DENYWRITE)
+				atomic_dec(&inode->i_writecount);
+			i_mmap_lock_write(mapping);
+			if (tmp->vm_flags & VM_SHARED)
+				atomic_inc(&mapping->i_mmap_writable);
+			flush_dcache_mmap_lock(mapping);
+			/* insert tmp into the share list, just after mpnt */
+			vma_interval_tree_insert_after(tmp, mpnt,
+					&mapping->i_mmap);
+			flush_dcache_mmap_unlock(mapping);
+			i_mmap_unlock_write(mapping);
+		}
+
+		/*
+		 * 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);
+
+		/*
+		 * Link in the new vma and copy the page table entries.
+		 */
+		*pprev = tmp;
+		pprev = &tmp->vm_next;
+		tmp->vm_prev = prev;
+		prev = tmp;
+
+		__vma_link_rb(mm, tmp, rb_link, rb_parent);
+		rb_link = &tmp->vm_rb.rb_right;
+		rb_parent = &tmp->vm_rb;
+		uksm_vma_add_new(tmp);
+		mm->map_count++;
+		retval = copy_page_range(mm, oldmm, mpnt);
+
+		if (tmp->vm_ops && tmp->vm_ops->open)
+			tmp->vm_ops->open(tmp);
+
+		if (retval)
+			goto out;
+	}
+	/* a new mm has just been created */
+	arch_dup_mmap(oldmm, mm);
+	retval = 0;
+out:
+	up_write(&mm->mmap_sem);
+	flush_tlb_mm(oldmm);
+	up_write(&oldmm->mmap_sem);
+	uprobe_end_dup_mmap();
+	return retval;
+fail_nomem_anon_vma_fork:
+	mpol_put(vma_policy(tmp));
+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)
+{
+	pgd_free(mm, mm->pgd);
+}
+#else
+static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
+{
+	down_write(&oldmm->mmap_sem);
+	RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
+	up_write(&oldmm->mmap_sem);
+	return 0;
+}
+#define mm_alloc_pgd(mm)	(0)
+#define mm_free_pgd(mm)
+#endif /* CONFIG_MMU */
+
+__cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
+
+#define allocate_mm()	(kmem_cache_alloc(mm_cachep, GFP_KERNEL))
+#define free_mm(mm)	(kmem_cache_free(mm_cachep, (mm)))
+
+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);
+
+#include <linux/init_task.h>
+
+static void mm_init_aio(struct mm_struct *mm)
+{
+#ifdef CONFIG_AIO
+	spin_lock_init(&mm->ioctx_lock);
+	mm->ioctx_table = NULL;
+#endif
+}
+
+static void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
+{
+#ifdef CONFIG_MEMCG
+	mm->owner = p;
+#endif
+}
+
+static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
+{
+	mm->mmap = NULL;
+	mm->mm_rb = RB_ROOT;
+	mm->vmacache_seqnum = 0;
+	atomic_set(&mm->mm_users, 1);
+	atomic_set(&mm->mm_count, 1);
+	init_rwsem(&mm->mmap_sem);
+	INIT_LIST_HEAD(&mm->mmlist);
+	mm->core_state = NULL;
+	atomic_long_set(&mm->nr_ptes, 0);
+	mm_nr_pmds_init(mm);
+	mm->map_count = 0;
+	mm->locked_vm = 0;
+	mm->pinned_vm = 0;
+	memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
+	spin_lock_init(&mm->page_table_lock);
+	mm_init_cpumask(mm);
+	mm_init_aio(mm);
+	mm_init_owner(mm, p);
+	mmu_notifier_mm_init(mm);
+	clear_tlb_flush_pending(mm);
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
+	mm->pmd_huge_pte = NULL;
+#endif
+
+	if (current->mm) {
+		mm->flags = current->mm->flags & MMF_INIT_MASK;
+		mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
+	} else {
+		mm->flags = default_dump_filter;
+		mm->def_flags = 0;
+	}
+
+	if (mm_alloc_pgd(mm))
+		goto fail_nopgd;
+
+	if (init_new_context(p, mm))
+		goto fail_nocontext;
+
+	return mm;
+
+fail_nocontext:
+	mm_free_pgd(mm);
+fail_nopgd:
+	free_mm(mm);
+	return NULL;
+}
+
+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);
+	}
+
+	if (atomic_long_read(&mm->nr_ptes))
+		pr_alert("BUG: non-zero nr_ptes on freeing mm: %ld\n",
+				atomic_long_read(&mm->nr_ptes));
+	if (mm_nr_pmds(mm))
+		pr_alert("BUG: non-zero nr_pmds on freeing mm: %ld\n",
+				mm_nr_pmds(mm));
+
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
+	VM_BUG_ON_MM(mm->pmd_huge_pte, mm);
+#endif
+}
+
+/*
+ * Allocate and initialize an mm_struct.
+ */
+struct mm_struct *mm_alloc(void)
+{
+	struct mm_struct *mm;
+
+	mm = allocate_mm();
+	if (!mm)
+		return NULL;
+
+	memset(mm, 0, sizeof(*mm));
+	return mm_init(mm, current);
+}
+
+/*
+ * 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.
+ */
+void __mmdrop(struct mm_struct *mm)
+{
+	BUG_ON(mm == &init_mm);
+	mm_free_pgd(mm);
+	destroy_context(mm);
+	mmu_notifier_mm_destroy(mm);
+	check_mm(mm);
+	free_mm(mm);
+}
+EXPORT_SYMBOL_GPL(__mmdrop);
+
+/*
+ * Decrement the use count and release all resources for an mm.
+ */
+void mmput(struct mm_struct *mm)
+{
+	might_sleep();
+
+	if (atomic_dec_and_test(&mm->mm_users)) {
+		uprobe_clear_state(mm);
+		exit_aio(mm);
+		ksm_exit(mm);
+		khugepaged_exit(mm); /* must run before exit_mmap */
+		exit_mmap(mm);
+		set_mm_exe_file(mm, NULL);
+		if (!list_empty(&mm->mmlist)) {
+			spin_lock(&mmlist_lock);
+			list_del(&mm->mmlist);
+			spin_unlock(&mmlist_lock);
+		}
+		if (mm->binfmt)
+			module_put(mm->binfmt->module);
+		mmdrop(mm);
+	}
+}
+EXPORT_SYMBOL_GPL(mmput);
+
+/**
+ * set_mm_exe_file - change a reference to the mm's executable file
+ *
+ * This changes mm's executable file (shown as symlink /proc/[pid]/exe).
+ *
+ * Main users are mmput() and sys_execve(). Callers prevent concurrent
+ * invocations: in mmput() nobody alive left, in execve task is single
+ * threaded. sys_prctl(PR_SET_MM_MAP/EXE_FILE) also needs to set the
+ * mm->exe_file, but does so without using set_mm_exe_file() in order
+ * to do avoid the need for any locks.
+ */
+void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
+{
+	struct file *old_exe_file;
+
+	/*
+	 * It is safe to dereference the exe_file without RCU as
+	 * this function is only called if nobody else can access
+	 * this mm -- see comment above for justification.
+	 */
+	old_exe_file = rcu_dereference_raw(mm->exe_file);
+
+	if (new_exe_file)
+		get_file(new_exe_file);
+	rcu_assign_pointer(mm->exe_file, new_exe_file);
+	if (old_exe_file)
+		fput(old_exe_file);
+}
+
+/**
+ * get_mm_exe_file - acquire a reference to the mm's executable file
+ *
+ * Returns %NULL if mm has no associated executable file.
+ * User must release file via fput().
+ */
+struct file *get_mm_exe_file(struct mm_struct *mm)
+{
+	struct file *exe_file;
+
+	rcu_read_lock();
+	exe_file = rcu_dereference(mm->exe_file);
+	if (exe_file && !get_file_rcu(exe_file))
+		exe_file = NULL;
+	rcu_read_unlock();
+	return exe_file;
+}
+EXPORT_SYMBOL(get_mm_exe_file);
+
+/**
+ * get_task_mm - acquire a reference to the task's mm
+ *
+ * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
+ * 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) {
+		if (task->flags & PF_KTHREAD)
+			mm = NULL;
+		else
+			atomic_inc(&mm->mm_users);
+	}
+	task_unlock(task);
+	return mm;
+}
+EXPORT_SYMBOL_GPL(get_task_mm);
+
+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 &&
+			!ptrace_may_access(task, mode)) {
+		mmput(mm);
+		mm = ERR_PTR(-EACCES);
+	}
+	mutex_unlock(&task->signal->cred_guard_mutex);
+
+	return mm;
+}
+
+static void complete_vfork_done(struct task_struct *tsk)
+{
+	struct completion *vfork;
+
+	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;
+}
+
+/* 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)
+{
+	/* Get rid of any futexes when releasing the mm */
+#ifdef CONFIG_FUTEX
+	if (unlikely(tsk->robust_list)) {
+		exit_robust_list(tsk);
+		tsk->robust_list = NULL;
+	}
+#ifdef CONFIG_COMPAT
+	if (unlikely(tsk->compat_robust_list)) {
+		compat_exit_robust_list(tsk);
+		tsk->compat_robust_list = NULL;
+	}
+#endif
+	if (unlikely(!list_empty(&tsk->pi_state_list)))
+		exit_pi_state_list(tsk);
+#endif
+
+	uprobe_free_utask(tsk);
+
+	/* Get rid of any cached register state */
+	deactivate_mm(tsk, mm);
+
+	/*
+	 * 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, say, a killed vfork parent shouldn't touch this mm.
+	 * Userland only wants this done for a sys_exit.
+	 */
+	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);
+		}
+		tsk->clear_child_tid = NULL;
+	}
+
+	/*
+	 * 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);
+}
+
+/*
+ * Allocate a new mm structure and copy contents from the
+ * mm structure of the passed in task structure.
+ */
+static struct mm_struct *dup_mm(struct task_struct *tsk)
+{
+	struct mm_struct *mm, *oldmm = current->mm;
+	int err;
+
+	mm = allocate_mm();
+	if (!mm)
+		goto fail_nomem;
+
+	memcpy(mm, oldmm, sizeof(*mm));
+
+	if (!mm_init(mm, tsk))
+		goto fail_nomem;
+
+	err = dup_mmap(mm, oldmm);
+	if (err)
+		goto free_pt;
+
+	mm->hiwater_rss = get_mm_rss(mm);
+	mm->hiwater_vm = mm->total_vm;
+
+	if (mm->binfmt && !try_module_get(mm->binfmt->module))
+		goto free_pt;
+
+	return mm;
+
+free_pt:
+	/* don't put binfmt in mmput, we haven't got module yet */
+	mm->binfmt = NULL;
+	mmput(mm);
+
+fail_nomem:
+	return NULL;
+}
+
+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;
+#ifdef CONFIG_DETECT_HUNG_TASK
+	tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
+#endif
+
+	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;
+
+	/* initialize the new vmacache entries */
+	vmacache_flush(tsk);
+
+	if (clone_flags & CLONE_VM) {
+		atomic_inc(&oldmm->mm_users);
+		mm = oldmm;
+		goto good_mm;
+	}
+
+	retval = -ENOMEM;
+	mm = dup_mm(tsk);
+	if (!mm)
+		goto fail_nomem;
+
+good_mm:
+	tsk->mm = mm;
+	tsk->active_mm = mm;
+	return 0;
+
+fail_nomem:
+	return retval;
+}
+
+static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
+{
+	struct fs_struct *fs = current->fs;
+	if (clone_flags & CLONE_FS) {
+		/* tsk->fs is already what we want */
+		spin_lock(&fs->lock);
+		if (fs->in_exec) {
+			spin_unlock(&fs->lock);
+			return -EAGAIN;
+		}
+		fs->users++;
+		spin_unlock(&fs->lock);
+		return 0;
+	}
+	tsk->fs = copy_fs_struct(fs);
+	if (!tsk->fs)
+		return -ENOMEM;
+	return 0;
+}
+
+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;
+}
+
+static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
+{
+#ifdef CONFIG_BLOCK
+	struct io_context *ioc = current->io_context;
+	struct io_context *new_ioc;
+
+	if (!ioc)
+		return 0;
+	/*
+	 * Share io context with parent, if CLONE_IO is set
+	 */
+	if (clone_flags & CLONE_IO) {
+		ioc_task_link(ioc);
+		tsk->io_context = ioc;
+	} else if (ioprio_valid(ioc->ioprio)) {
+		new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
+		if (unlikely(!new_ioc))
+			return -ENOMEM;
+
+		new_ioc->ioprio = ioc->ioprio;
+		put_io_context(new_ioc);
+	}
+#endif
+	return 0;
+}
+
+static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
+{
+	struct sighand_struct *sig;
+
+	if (clone_flags & CLONE_SIGHAND) {
+		atomic_inc(&current->sighand->count);
+		return 0;
+	}
+	sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
+	rcu_assign_pointer(tsk->sighand, sig);
+	if (!sig)
+		return -ENOMEM;
+	atomic_set(&sig->count, 1);
+	memcpy(sig->action, current->sighand->action, sizeof(sig->action));
+	return 0;
+}
+
+void __cleanup_sighand(struct sighand_struct *sighand)
+{
+	if (atomic_dec_and_test(&sighand->count)) {
+		signalfd_cleanup(sighand);
+		/*
+		 * sighand_cachep is SLAB_DESTROY_BY_RCU so we can free it
+		 * without an RCU grace period, see __lock_task_sighand().
+		 */
+		kmem_cache_free(sighand_cachep, sighand);
+	}
+}
+
+/*
+ * Initialize POSIX timer handling for a thread group.
+ */
+static void posix_cpu_timers_init_group(struct signal_struct *sig)
+{
+	unsigned long cpu_limit;
+
+	/* Thread group counters. */
+	thread_group_cputime_init(sig);
+
+	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);
+		sig->cputimer.running = 1;
+	}
+
+	/* The timer lists. */
+	INIT_LIST_HEAD(&sig->cpu_timers[0]);
+	INIT_LIST_HEAD(&sig->cpu_timers[1]);
+	INIT_LIST_HEAD(&sig->cpu_timers[2]);
+}
+
+static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
+{
+	struct signal_struct *sig;
+
+	if (clone_flags & CLONE_THREAD)
+		return 0;
+
+	sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
+	tsk->signal = sig;
+	if (!sig)
+		return -ENOMEM;
+
+	sig->nr_threads = 1;
+	atomic_set(&sig->live, 1);
+	atomic_set(&sig->sigcnt, 1);
+
+	/* 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);
+
+	init_waitqueue_head(&sig->wait_chldexit);
+	sig->curr_target = tsk;
+	init_sigpending(&sig->shared_pending);
+	INIT_LIST_HEAD(&sig->posix_timers);
+	seqlock_init(&sig->stats_lock);
+
+	hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	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);
+
+	posix_cpu_timers_init_group(sig);
+
+	tty_audit_fork(sig);
+	sched_autogroup_fork(sig);
+
+#ifdef CONFIG_CGROUPS
+	init_rwsem(&sig->group_rwsem);
+#endif
+
+	sig->oom_score_adj = current->signal->oom_score_adj;
+	sig->oom_score_adj_min = current->signal->oom_score_adj_min;
+
+	sig->has_child_subreaper = current->signal->has_child_subreaper ||
+				   current->signal->is_child_subreaper;
+
+	mutex_init(&sig->cred_guard_mutex);
+
+	return 0;
+}
+
+static void copy_seccomp(struct task_struct *p)
+{
+#ifdef CONFIG_SECCOMP
+	/*
+	 * Must be called with sighand->lock held, which is common to
+	 * all threads in the group. Holding cred_guard_mutex is not
+	 * needed because this new task is not yet running and cannot
+	 * be racing exec.
+	 */
+	assert_spin_locked(&current->sighand->siglock);
+
+	/* Ref-count the new filter user, and assign it. */
+	get_seccomp_filter(current);
+	p->seccomp = current->seccomp;
+
+	/*
+	 * Explicitly enable no_new_privs here in case it got set
+	 * between the task_struct being duplicated and holding the
+	 * sighand lock. The seccomp state and nnp must be in sync.
+	 */
+	if (task_no_new_privs(current))
+		task_set_no_new_privs(p);
+
+	/*
+	 * If the parent gained a seccomp mode after copying thread
+	 * flags and between before we held the sighand lock, we have
+	 * to manually enable the seccomp thread flag here.
+	 */
+	if (p->seccomp.mode != SECCOMP_MODE_DISABLED)
+		set_tsk_thread_flag(p, TIF_SECCOMP);
+#endif
+}
+
+SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
+{
+	current->clear_child_tid = tidptr;
+
+	return task_pid_vnr(current);
+}
+
+static void rt_mutex_init_task(struct task_struct *p)
+{
+	raw_spin_lock_init(&p->pi_lock);
+#ifdef CONFIG_RT_MUTEXES
+	p->pi_waiters = RB_ROOT;
+	p->pi_waiters_leftmost = NULL;
+	p->pi_blocked_on = NULL;
+#endif
+}
+
+/*
+ * Initialize POSIX timer handling for a single task.
+ */
+static void posix_cpu_timers_init(struct task_struct *tsk)
+{
+	tsk->cputime_expires.prof_exp = 0;
+	tsk->cputime_expires.virt_exp = 0;
+	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]);
+}
+
+static inline void
+init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
+{
+	 task->pids[type].pid = pid;
+}
+
+/*
+ * 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.
+ */
+static struct task_struct *copy_process(unsigned long clone_flags,
+					unsigned long stack_start,
+					unsigned long stack_size,
+					int __user *child_tidptr,
+					struct pid *pid,
+					int trace)
+{
+	int retval;
+	struct task_struct *p;
+
+	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
+		return ERR_PTR(-EINVAL);
+
+	if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|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);
+
+	/*
+	 * 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);
+
+	/*
+	 * If the new process will be in a different pid or user namespace
+	 * do not allow it to share a thread group or signal handlers or
+	 * parent with the forking task.
+	 */
+	if (clone_flags & CLONE_SIGHAND) {
+		if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
+		    (task_active_pid_ns(current) !=
+				current->nsproxy->pid_ns_for_children))
+			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;
+
+	ftrace_graph_init_task(p);
+
+	rt_mutex_init_task(p);
+
+#ifdef CONFIG_PROVE_LOCKING
+	DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
+	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
+#endif
+	retval = -EAGAIN;
+	if (atomic_read(&p->real_cred->user->processes) >=
+			task_rlimit(p, RLIMIT_NPROC)) {
+		if (p->real_cred->user != INIT_USER &&
+		    !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
+			goto bad_fork_free;
+	}
+	current->flags &= ~PF_NPROC_EXCEEDED;
+
+	retval = copy_creds(p, clone_flags);
+	if (retval < 0)
+		goto bad_fork_free;
+
+	/*
+	 * 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.
+	 */
+	retval = -EAGAIN;
+	if (nr_threads >= max_threads)
+		goto bad_fork_cleanup_count;
+
+	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */
+	p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
+	p->flags |= PF_FORKNOEXEC;
+	INIT_LIST_HEAD(&p->children);
+	INIT_LIST_HEAD(&p->sibling);
+	rcu_copy_process(p);
+	p->vfork_done = NULL;
+	spin_lock_init(&p->alloc_lock);
+
+	init_sigpending(&p->pending);
+
+	p->utime = p->stime = p->gtime = 0;
+	p->utimescaled = p->stimescaled = 0;
+#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
+	p->prev_cputime.utime = p->prev_cputime.stime = 0;
+#endif
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
+	seqlock_init(&p->vtime_seqlock);
+	p->vtime_snap = 0;
+	p->vtime_snap_whence = VTIME_SLEEPING;
+#endif
+
+#if defined(SPLIT_RSS_COUNTING)
+	memset(&p->rss_stat, 0, sizeof(p->rss_stat));
+#endif
+
+	p->default_timer_slack_ns = current->timer_slack_ns;
+
+	task_io_accounting_init(&p->ioac);
+	acct_clear_integrals(p);
+
+	posix_cpu_timers_init(p);
+
+	p->start_time = ktime_get_ns();
+	p->real_start_time = ktime_get_boot_ns();
+	p->io_context = NULL;
+	p->audit_context = NULL;
+	if (clone_flags & CLONE_THREAD)
+		threadgroup_change_begin(current);
+	cgroup_fork(p);
+#ifdef CONFIG_NUMA
+	p->mempolicy = mpol_dup(p->mempolicy);
+	if (IS_ERR(p->mempolicy)) {
+		retval = PTR_ERR(p->mempolicy);
+		p->mempolicy = NULL;
+		goto bad_fork_cleanup_threadgroup_lock;
+	}
+#endif
+#ifdef CONFIG_CPUSETS
+	p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
+	p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
+	seqcount_init(&p->mems_allowed_seq);
+#endif
+#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
+#ifdef CONFIG_LOCKDEP
+	p->lockdep_depth = 0; /* no locks held yet */
+	p->curr_chain_key = 0;
+	p->lockdep_recursion = 0;
+#endif
+
+#ifdef CONFIG_DEBUG_MUTEXES
+	p->blocked_on = NULL; /* not blocked yet */
+#endif
+#ifdef CONFIG_BCACHE
+	p->sequential_io	= 0;
+	p->sequential_io_avg	= 0;
+#endif
+
+	/* Perform scheduler related setup. Assign this task to a CPU. */
+	retval = sched_fork(clone_flags, p);
+	if (retval)
+		goto bad_fork_cleanup_policy;
+
+	retval = perf_event_init_task(p);
+	if (retval)
+		goto bad_fork_cleanup_policy;
+	retval = audit_alloc(p);
+	if (retval)
+		goto bad_fork_cleanup_perf;
+	/* copy all the process information */
+	shm_init_task(p);
+	retval = copy_semundo(clone_flags, p);
+	if (retval)
+		goto bad_fork_cleanup_audit;
+	retval = copy_files(clone_flags, p);
+	if (retval)
+		goto bad_fork_cleanup_semundo;
+	retval = copy_fs(clone_flags, p);
+	if (retval)
+		goto bad_fork_cleanup_files;
+	retval = copy_sighand(clone_flags, p);
+	if (retval)
+		goto bad_fork_cleanup_fs;
+	retval = copy_signal(clone_flags, p);
+	if (retval)
+		goto bad_fork_cleanup_sighand;
+	retval = copy_mm(clone_flags, p);
+	if (retval)
+		goto bad_fork_cleanup_signal;
+	retval = copy_namespaces(clone_flags, p);
+	if (retval)
+		goto bad_fork_cleanup_mm;
+	retval = copy_io(clone_flags, p);
+	if (retval)
+		goto bad_fork_cleanup_namespaces;
+	retval = copy_thread(clone_flags, stack_start, stack_size, p);
+	if (retval)
+		goto bad_fork_cleanup_io;
+
+	if (pid != &init_struct_pid) {
+		pid = alloc_pid(p->nsproxy->pid_ns_for_children);
+		if (IS_ERR(pid)) {
+			retval = PTR_ERR(pid);
+			goto bad_fork_cleanup_io;
+		}
+	}
+
+	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;
+#ifdef CONFIG_BLOCK
+	p->plug = NULL;
+#endif
+#ifdef CONFIG_FUTEX
+	p->robust_list = NULL;
+#ifdef CONFIG_COMPAT
+	p->compat_robust_list = NULL;
+#endif
+	INIT_LIST_HEAD(&p->pi_state_list);
+	p->pi_state_cache = NULL;
+#endif
+	/*
+	 * 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;
+
+	/*
+	 * Syscall tracing and stepping should be turned off in the
+	 * child regardless of CLONE_PTRACE.
+	 */
+	user_disable_single_step(p);
+	clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
+#ifdef TIF_SYSCALL_EMU
+	clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
+#endif
+	clear_all_latency_tracing(p);
+
+	/* ok, now we should be set up.. */
+	p->pid = pid_nr(pid);
+	if (clone_flags & CLONE_THREAD) {
+		p->exit_signal = -1;
+		p->group_leader = current->group_leader;
+		p->tgid = current->tgid;
+	} else {
+		if (clone_flags & CLONE_PARENT)
+			p->exit_signal = current->group_leader->exit_signal;
+		else
+			p->exit_signal = (clone_flags & CSIGNAL);
+		p->group_leader = p;
+		p->tgid = p->pid;
+	}
+
+	p->nr_dirtied = 0;
+	p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
+	p->dirty_paused_when = 0;
+
+	p->pdeath_signal = 0;
+	INIT_LIST_HEAD(&p->thread_group);
+	p->task_works = NULL;
+
+	/*
+	 * Make it visible to the rest of the system, but dont wake it up yet.
+	 * Need tasklist lock for parent etc handling!
+	 */
+	write_lock_irq(&tasklist_lock);
+
+	/* CLONE_PARENT re-uses the old parent */
+	if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
+		p->real_parent = current->real_parent;
+		p->parent_exec_id = current->parent_exec_id;
+	} else {
+		p->real_parent = current;
+		p->parent_exec_id = current->self_exec_id;
+	}
+
+	spin_lock(&current->sighand->siglock);
+
+	/*
+	 * Copy seccomp details explicitly here, in case they were changed
+	 * before holding sighand lock.
+	 */
+	copy_seccomp(p);
+
+	/*
+	 * 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).
+	*/
+	recalc_sigpending();
+	if (signal_pending(current)) {
+		spin_unlock(&current->sighand->siglock);
+		write_unlock_irq(&tasklist_lock);
+		retval = -ERESTARTNOINTR;
+		goto bad_fork_free_pid;
+	}
+
+	if (likely(p->pid)) {
+		ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
+
+		init_task_pid(p, PIDTYPE_PID, pid);
+		if (thread_group_leader(p)) {
+			init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
+			init_task_pid(p, PIDTYPE_SID, task_session(current));
+
+			if (is_child_reaper(pid)) {
+				ns_of_pid(pid)->child_reaper = p;
+				p->signal->flags |= SIGNAL_UNKILLABLE;
+			}
+
+			p->signal->leader_pid = pid;
+			p->signal->tty = tty_kref_get(current->signal->tty);
+			list_add_tail(&p->sibling, &p->real_parent->children);
+			list_add_tail_rcu(&p->tasks, &init_task.tasks);
+			attach_pid(p, PIDTYPE_PGID);
+			attach_pid(p, PIDTYPE_SID);
+			__this_cpu_inc(process_counts);
+		} else {
+			current->signal->nr_threads++;
+			atomic_inc(&current->signal->live);
+			atomic_inc(&current->signal->sigcnt);
+			list_add_tail_rcu(&p->thread_group,
+					  &p->group_leader->thread_group);
+			list_add_tail_rcu(&p->thread_node,
+					  &p->signal->thread_head);
+		}
+		attach_pid(p, PIDTYPE_PID);
+		nr_threads++;
+	}
+
+	total_forks++;
+	spin_unlock(&current->sighand->siglock);
+	syscall_tracepoint_update(p);
+	write_unlock_irq(&tasklist_lock);
+
+	proc_fork_connector(p);
+	cgroup_post_fork(p);
+	if (clone_flags & CLONE_THREAD)
+		threadgroup_change_end(current);
+	perf_event_fork(p);
+
+	trace_task_newtask(p, clone_flags);
+	uprobe_copy_process(p, clone_flags);
+
+	return p;
+
+bad_fork_free_pid:
+	if (pid != &init_struct_pid)
+		free_pid(pid);
+bad_fork_cleanup_io:
+	if (p->io_context)
+		exit_io_context(p);
+bad_fork_cleanup_namespaces:
+	exit_task_namespaces(p);
+bad_fork_cleanup_mm:
+	if (p->mm)
+		mmput(p->mm);
+bad_fork_cleanup_signal:
+	if (!(clone_flags & CLONE_THREAD))
+		free_signal_struct(p->signal);
+bad_fork_cleanup_sighand:
+	__cleanup_sighand(p->sighand);
+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_perf:
+	perf_event_free_task(p);
+bad_fork_cleanup_policy:
+#ifdef CONFIG_NUMA
+	mpol_put(p->mempolicy);
+bad_fork_cleanup_threadgroup_lock:
+#endif
+	if (clone_flags & CLONE_THREAD)
+		threadgroup_change_end(current);
+	delayacct_tsk_free(p);
+bad_fork_cleanup_count:
+	atomic_dec(&p->cred->user->processes);
+	exit_creds(p);
+bad_fork_free:
+	free_task(p);
+fork_out:
+	return ERR_PTR(retval);
+}
+
+static inline void init_idle_pids(struct pid_link *links)
+{
+	enum pid_type type;
+
+	for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
+		INIT_HLIST_NODE(&links[type].node); /* not really needed */
+		links[type].pid = &init_struct_pid;
+	}
+}
+
+struct task_struct *fork_idle(int cpu)
+{
+	struct task_struct *task;
+	task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0);
+	if (!IS_ERR(task)) {
+		init_idle_pids(task->pids);
+		init_idle(task, cpu);
+	}
+
+	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,
+	      unsigned long stack_size,
+	      int __user *parent_tidptr,
+	      int __user *child_tidptr)
+{
+	struct task_struct *p;
+	int trace = 0;
+	long nr;
+
+	/*
+	 * Determine whether and which event to report to ptracer.  When
+	 * called from kernel_thread or CLONE_UNTRACED is explicitly
+	 * requested, no event is reported; otherwise, report if the event
+	 * for the type of forking is enabled.
+	 */
+	if (!(clone_flags & CLONE_UNTRACED)) {
+		if (clone_flags & CLONE_VFORK)
+			trace = PTRACE_EVENT_VFORK;
+		else if ((clone_flags & CSIGNAL) != SIGCHLD)
+			trace = PTRACE_EVENT_CLONE;
+		else
+			trace = PTRACE_EVENT_FORK;
+
+		if (likely(!ptrace_event_enabled(current, trace)))
+			trace = 0;
+	}
+
+	p = copy_process(clone_flags, stack_start, stack_size,
+			 child_tidptr, NULL, trace);
+	/*
+	 * 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;
+		struct pid *pid;
+
+		trace_sched_process_fork(current, p);
+
+		pid = get_task_pid(p, PIDTYPE_PID);
+		nr = pid_vnr(pid);
+
+		if (clone_flags & CLONE_PARENT_SETTID)
+			put_user(nr, parent_tidptr);
+
+		if (clone_flags & CLONE_VFORK) {
+			p->vfork_done = &vfork;
+			init_completion(&vfork);
+			get_task_struct(p);
+		}
+
+		wake_up_new_task(p);
+
+		/* forking complete and child started to run, tell ptracer */
+		if (unlikely(trace))
+			ptrace_event_pid(trace, pid);
+
+		if (clone_flags & CLONE_VFORK) {
+			if (!wait_for_vfork_done(p, &vfork))
+				ptrace_event_pid(PTRACE_EVENT_VFORK_DONE, pid);
+		}
+
+		put_pid(pid);
+	} else {
+		nr = PTR_ERR(p);
+	}
+	return nr;
+}
+
+/*
+ * Create a kernel thread.
+ */
+pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
+{
+	return do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
+		(unsigned long)arg, NULL, NULL);
+}
+
+#ifdef __ARCH_WANT_SYS_FORK
+SYSCALL_DEFINE0(fork)
+{
+#ifdef CONFIG_MMU
+	return do_fork(SIGCHLD, 0, 0, NULL, NULL);
+#else
+	/* can not support in nommu mode */
+	return -EINVAL;
+#endif
+}
+#endif
+
+#ifdef __ARCH_WANT_SYS_VFORK
+SYSCALL_DEFINE0(vfork)
+{
+	return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0,
+			0, NULL, NULL);
+}
+#endif
+
+#ifdef __ARCH_WANT_SYS_CLONE
+#ifdef CONFIG_CLONE_BACKWARDS
+SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
+		 int __user *, parent_tidptr,
+		 int, tls_val,
+		 int __user *, child_tidptr)
+#elif defined(CONFIG_CLONE_BACKWARDS2)
+SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
+		 int __user *, parent_tidptr,
+		 int __user *, child_tidptr,
+		 int, tls_val)
+#elif defined(CONFIG_CLONE_BACKWARDS3)
+SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
+		int, stack_size,
+		int __user *, parent_tidptr,
+		int __user *, child_tidptr,
+		int, tls_val)
+#else
+SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
+		 int __user *, parent_tidptr,
+		 int __user *, child_tidptr,
+		 int, tls_val)
+#endif
+{
+	return do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr);
+}
+#endif
+
+#ifndef ARCH_MIN_MMSTRUCT_ALIGN
+#define ARCH_MIN_MMSTRUCT_ALIGN 0
+#endif
+
+static void sighand_ctor(void *data)
+{
+	struct sighand_struct *sighand = data;
+
+	spin_lock_init(&sighand->siglock);
+	init_waitqueue_head(&sighand->signalfd_wqh);
+}
+
+void __init proc_caches_init(void)
+{
+	sighand_cachep = kmem_cache_create("sighand_cache",
+			sizeof(struct sighand_struct), 0,
+			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
+			SLAB_NOTRACK, sighand_ctor);
+	signal_cachep = kmem_cache_create("signal_cache",
+			sizeof(struct signal_struct), 0,
+			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
+	files_cachep = kmem_cache_create("files_cache",
+			sizeof(struct files_struct), 0,
+			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
+	fs_cachep = kmem_cache_create("fs_cache",
+			sizeof(struct fs_struct), 0,
+			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
+	/*
+	 * FIXME! The "sizeof(struct mm_struct)" currently includes the
+	 * whole struct cpumask for the OFFSTACK case. We could change
+	 * this to *only* allocate as much of it as required by the
+	 * maximum number of CPU's we can ever have.  The cpumask_allocation
+	 * is at the end of the structure, exactly for that reason.
+	 */
+	mm_cachep = kmem_cache_create("mm_struct",
+			sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
+			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
+	vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
+	mmap_init();
+	nsproxy_cache_init();
+}
+
+/*
+ * Check constraints on flags passed to the unshare system call.
+ */
+static int check_unshare_flags(unsigned long unshare_flags)
+{
+	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
+				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
+				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
+				CLONE_NEWUSER|CLONE_NEWPID))
+		return -EINVAL;
+	/*
+	 * Not implemented, but pretend it works if there is nothing to
+	 * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
+	 * needs to unshare vm.
+	 */
+	if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
+		/* FIXME: get_task_mm() increments ->mm_users */
+		if (atomic_read(&current->mm->mm_users) > 1)
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
+/*
+ * Unshare the filesystem structure if it is being shared
+ */
+static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
+{
+	struct fs_struct *fs = current->fs;
+
+	if (!(unshare_flags & CLONE_FS) || !fs)
+		return 0;
+
+	/* don't need lock here; in the worst case we'll do useless copy */
+	if (fs->users == 1)
+		return 0;
+
+	*new_fsp = copy_fs_struct(fs);
+	if (!*new_fsp)
+		return -ENOMEM;
+
+	return 0;
+}
+
+/*
+ * Unshare file descriptor table if it is being shared
+ */
+static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
+{
+	struct files_struct *fd = current->files;
+	int error = 0;
+
+	if ((unshare_flags & CLONE_FILES) &&
+	    (fd && atomic_read(&fd->count) > 1)) {
+		*new_fdp = dup_fd(fd, &error);
+		if (!*new_fdp)
+			return error;
+	}
+
+	return 0;
+}
+
+/*
+ * unshare allows a process to 'unshare' part of the process
+ * context which was originally shared using clone.  copy_*
+ * functions used by do_fork() cannot be used here directly
+ * because they modify an inactive task_struct that is being
+ * constructed. Here we are modifying the current, active,
+ * task_struct.
+ */
+SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
+{
+	struct fs_struct *fs, *new_fs = NULL;
+	struct files_struct *fd, *new_fd = NULL;
+	struct cred *new_cred = NULL;
+	struct nsproxy *new_nsproxy = NULL;
+	int do_sysvsem = 0;
+	int err;
+
+	/*
+	 * If unsharing a user namespace must also unshare the thread.
+	 */
+	if (unshare_flags & CLONE_NEWUSER)
+		unshare_flags |= CLONE_THREAD | CLONE_FS;
+	/*
+	 * If unsharing a thread from a thread group, must also unshare vm.
+	 */
+	if (unshare_flags & CLONE_THREAD)
+		unshare_flags |= CLONE_VM;
+	/*
+	 * If unsharing vm, must also unshare signal handlers.
+	 */
+	if (unshare_flags & CLONE_VM)
+		unshare_flags |= CLONE_SIGHAND;
+	/*
+	 * If unsharing namespace, must also unshare filesystem information.
+	 */
+	if (unshare_flags & CLONE_NEWNS)
+		unshare_flags |= CLONE_FS;
+
+	err = check_unshare_flags(unshare_flags);
+	if (err)
+		goto bad_unshare_out;
+	/*
+	 * CLONE_NEWIPC must also detach from the undolist: after switching
+	 * to a new ipc namespace, the semaphore arrays from the old
+	 * namespace are unreachable.
+	 */
+	if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
+		do_sysvsem = 1;
+	err = unshare_fs(unshare_flags, &new_fs);
+	if (err)
+		goto bad_unshare_out;
+	err = unshare_fd(unshare_flags, &new_fd);
+	if (err)
+		goto bad_unshare_cleanup_fs;
+	err = unshare_userns(unshare_flags, &new_cred);
+	if (err)
+		goto bad_unshare_cleanup_fd;
+	err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
+					 new_cred, new_fs);
+	if (err)
+		goto bad_unshare_cleanup_cred;
+
+	if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
+		if (do_sysvsem) {
+			/*
+			 * CLONE_SYSVSEM is equivalent to sys_exit().
+			 */
+			exit_sem(current);
+		}
+		if (unshare_flags & CLONE_NEWIPC) {
+			/* Orphan segments in old ns (see sem above). */
+			exit_shm(current);
+			shm_init_task(current);
+		}
+
+		if (new_nsproxy)
+			switch_task_namespaces(current, new_nsproxy);
+
+		task_lock(current);
+
+		if (new_fs) {
+			fs = current->fs;
+			spin_lock(&fs->lock);
+			current->fs = new_fs;
+			if (--fs->users)
+				new_fs = NULL;
+			else
+				new_fs = fs;
+			spin_unlock(&fs->lock);
+		}
+
+		if (new_fd) {
+			fd = current->files;
+			current->files = new_fd;
+			new_fd = fd;
+		}
+
+		task_unlock(current);
+
+		if (new_cred) {
+			/* Install the new user namespace */
+			commit_creds(new_cred);
+			new_cred = NULL;
+		}
+	}
+
+bad_unshare_cleanup_cred:
+	if (new_cred)
+		put_cred(new_cred);
+bad_unshare_cleanup_fd:
+	if (new_fd)
+		put_files_struct(new_fd);
+
+bad_unshare_cleanup_fs:
+	if (new_fs)
+		free_fs_struct(new_fs);
+
+bad_unshare_out:
+	return err;
+}
+
+/*
+ *	Helper to unshare the files of the current task.
+ *	We don't want to expose copy_files internals to
+ *	the exec layer of the kernel.
+ */
+
+int unshare_files(struct files_struct **displaced)
+{
+	struct task_struct *task = current;
+	struct files_struct *copy = NULL;
+	int error;
+
+	error = unshare_fd(CLONE_FILES, &copy);
+	if (error || !copy) {
+		*displaced = NULL;
+		return error;
+	}
+	*displaced = task->files;
+	task_lock(task);
+	task->files = copy;
+	task_unlock(task);
+	return 0;
+}
+
+int sysctl_max_threads(struct ctl_table *table, int write,
+		       void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct ctl_table t;
+	int ret;
+	int threads = max_threads;
+	int min = MIN_THREADS;
+	int max = MAX_THREADS;
+
+	t = *table;
+	t.data = &threads;
+	t.extra1 = &min;
+	t.extra2 = &max;
+
+	ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
+	if (ret || !write)
+		return ret;
+
+	set_max_threads(threads);
+
+	return 0;
+}