Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3554 insertions, 0 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
new file mode 100644
index 0000000000..177ce7438d
--- /dev/null
+++ b/kernel/fork.c
@@ -0,0 +1,3554 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  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/anon_inodes.h>
+#include <linux/slab.h>
+#include <linux/sched/autogroup.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/coredump.h>
+#include <linux/sched/user.h>
+#include <linux/sched/numa_balancing.h>
+#include <linux/sched/stat.h>
+#include <linux/sched/task.h>
+#include <linux/sched/task_stack.h>
+#include <linux/sched/cputime.h>
+#include <linux/seq_file.h>
+#include <linux/rtmutex.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/kmsan.h>
+#include <linux/binfmts.h>
+#include <linux/mman.h>
+#include <linux/mmu_notifier.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/mm_inline.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/userfaultfd_k.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/tty.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 <linux/kcov.h>
+#include <linux/livepatch.h>
+#include <linux/thread_info.h>
+#include <linux/stackleak.h>
+#include <linux/kasan.h>
+#include <linux/scs.h>
+#include <linux/io_uring.h>
+#include <linux/bpf.h>
+#include <linux/stackprotector.h>
+#include <linux/user_events.h>
+#include <linux/iommu.h>
+
+#include <asm/pgalloc.h>
+#include <linux/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.. */
+
+static int max_threads;		/* tunable limit on nr_threads */
+
+#define NAMED_ARRAY_INDEX(x)	[x] = __stringify(x)
+
+static const char * const resident_page_types[] = {
+	NAMED_ARRAY_INDEX(MM_FILEPAGES),
+	NAMED_ARRAY_INDEX(MM_ANONPAGES),
+	NAMED_ARRAY_INDEX(MM_SWAPENTS),
+	NAMED_ARRAY_INDEX(MM_SHMEMPAGES),
+};
+
+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, node);
+}
+
+static inline void free_task_struct(struct task_struct *tsk)
+{
+	kmem_cache_free(task_struct_cachep, tsk);
+}
+#endif
+
+#ifndef CONFIG_ARCH_THREAD_STACK_ALLOCATOR
+
+/*
+ * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
+ * kmemcache based allocator.
+ */
+# if THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK)
+
+#  ifdef CONFIG_VMAP_STACK
+/*
+ * vmalloc() is a bit slow, and calling vfree() enough times will force a TLB
+ * flush.  Try to minimize the number of calls by caching stacks.
+ */
+#define NR_CACHED_STACKS 2
+static DEFINE_PER_CPU(struct vm_struct *, cached_stacks[NR_CACHED_STACKS]);
+
+struct vm_stack {
+	struct rcu_head rcu;
+	struct vm_struct *stack_vm_area;
+};
+
+static bool try_release_thread_stack_to_cache(struct vm_struct *vm)
+{
+	unsigned int i;
+
+	for (i = 0; i < NR_CACHED_STACKS; i++) {
+		if (this_cpu_cmpxchg(cached_stacks[i], NULL, vm) != NULL)
+			continue;
+		return true;
+	}
+	return false;
+}
+
+static void thread_stack_free_rcu(struct rcu_head *rh)
+{
+	struct vm_stack *vm_stack = container_of(rh, struct vm_stack, rcu);
+
+	if (try_release_thread_stack_to_cache(vm_stack->stack_vm_area))
+		return;
+
+	vfree(vm_stack);
+}
+
+static void thread_stack_delayed_free(struct task_struct *tsk)
+{
+	struct vm_stack *vm_stack = tsk->stack;
+
+	vm_stack->stack_vm_area = tsk->stack_vm_area;
+	call_rcu(&vm_stack->rcu, thread_stack_free_rcu);
+}
+
+static int free_vm_stack_cache(unsigned int cpu)
+{
+	struct vm_struct **cached_vm_stacks = per_cpu_ptr(cached_stacks, cpu);
+	int i;
+
+	for (i = 0; i < NR_CACHED_STACKS; i++) {
+		struct vm_struct *vm_stack = cached_vm_stacks[i];
+
+		if (!vm_stack)
+			continue;
+
+		vfree(vm_stack->addr);
+		cached_vm_stacks[i] = NULL;
+	}
+
+	return 0;
+}
+
+static int memcg_charge_kernel_stack(struct vm_struct *vm)
+{
+	int i;
+	int ret;
+	int nr_charged = 0;
+
+	BUG_ON(vm->nr_pages != THREAD_SIZE / PAGE_SIZE);
+
+	for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
+		ret = memcg_kmem_charge_page(vm->pages[i], GFP_KERNEL, 0);
+		if (ret)
+			goto err;
+		nr_charged++;
+	}
+	return 0;
+err:
+	for (i = 0; i < nr_charged; i++)
+		memcg_kmem_uncharge_page(vm->pages[i], 0);
+	return ret;
+}
+
+static int alloc_thread_stack_node(struct task_struct *tsk, int node)
+{
+	struct vm_struct *vm;
+	void *stack;
+	int i;
+
+	for (i = 0; i < NR_CACHED_STACKS; i++) {
+		struct vm_struct *s;
+
+		s = this_cpu_xchg(cached_stacks[i], NULL);
+
+		if (!s)
+			continue;
+
+		/* Reset stack metadata. */
+		kasan_unpoison_range(s->addr, THREAD_SIZE);
+
+		stack = kasan_reset_tag(s->addr);
+
+		/* Clear stale pointers from reused stack. */
+		memset(stack, 0, THREAD_SIZE);
+
+		if (memcg_charge_kernel_stack(s)) {
+			vfree(s->addr);
+			return -ENOMEM;
+		}
+
+		tsk->stack_vm_area = s;
+		tsk->stack = stack;
+		return 0;
+	}
+
+	/*
+	 * Allocated stacks are cached and later reused by new threads,
+	 * so memcg accounting is performed manually on assigning/releasing
+	 * stacks to tasks. Drop __GFP_ACCOUNT.
+	 */
+	stack = __vmalloc_node_range(THREAD_SIZE, THREAD_ALIGN,
+				     VMALLOC_START, VMALLOC_END,
+				     THREADINFO_GFP & ~__GFP_ACCOUNT,
+				     PAGE_KERNEL,
+				     0, node, __builtin_return_address(0));
+	if (!stack)
+		return -ENOMEM;
+
+	vm = find_vm_area(stack);
+	if (memcg_charge_kernel_stack(vm)) {
+		vfree(stack);
+		return -ENOMEM;
+	}
+	/*
+	 * We can't call find_vm_area() in interrupt context, and
+	 * free_thread_stack() can be called in interrupt context,
+	 * so cache the vm_struct.
+	 */
+	tsk->stack_vm_area = vm;
+	stack = kasan_reset_tag(stack);
+	tsk->stack = stack;
+	return 0;
+}
+
+static void free_thread_stack(struct task_struct *tsk)
+{
+	if (!try_release_thread_stack_to_cache(tsk->stack_vm_area))
+		thread_stack_delayed_free(tsk);
+
+	tsk->stack = NULL;
+	tsk->stack_vm_area = NULL;
+}
+
+#  else /* !CONFIG_VMAP_STACK */
+
+static void thread_stack_free_rcu(struct rcu_head *rh)
+{
+	__free_pages(virt_to_page(rh), THREAD_SIZE_ORDER);
+}
+
+static void thread_stack_delayed_free(struct task_struct *tsk)
+{
+	struct rcu_head *rh = tsk->stack;
+
+	call_rcu(rh, thread_stack_free_rcu);
+}
+
+static int alloc_thread_stack_node(struct task_struct *tsk, int node)
+{
+	struct page *page = alloc_pages_node(node, THREADINFO_GFP,
+					     THREAD_SIZE_ORDER);
+
+	if (likely(page)) {
+		tsk->stack = kasan_reset_tag(page_address(page));
+		return 0;
+	}
+	return -ENOMEM;
+}
+
+static void free_thread_stack(struct task_struct *tsk)
+{
+	thread_stack_delayed_free(tsk);
+	tsk->stack = NULL;
+}
+
+#  endif /* CONFIG_VMAP_STACK */
+# else /* !(THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK)) */
+
+static struct kmem_cache *thread_stack_cache;
+
+static void thread_stack_free_rcu(struct rcu_head *rh)
+{
+	kmem_cache_free(thread_stack_cache, rh);
+}
+
+static void thread_stack_delayed_free(struct task_struct *tsk)
+{
+	struct rcu_head *rh = tsk->stack;
+
+	call_rcu(rh, thread_stack_free_rcu);
+}
+
+static int alloc_thread_stack_node(struct task_struct *tsk, int node)
+{
+	unsigned long *stack;
+	stack = kmem_cache_alloc_node(thread_stack_cache, THREADINFO_GFP, node);
+	stack = kasan_reset_tag(stack);
+	tsk->stack = stack;
+	return stack ? 0 : -ENOMEM;
+}
+
+static void free_thread_stack(struct task_struct *tsk)
+{
+	thread_stack_delayed_free(tsk);
+	tsk->stack = NULL;
+}
+
+void thread_stack_cache_init(void)
+{
+	thread_stack_cache = kmem_cache_create_usercopy("thread_stack",
+					THREAD_SIZE, THREAD_SIZE, 0, 0,
+					THREAD_SIZE, NULL);
+	BUG_ON(thread_stack_cache == NULL);
+}
+
+# endif /* THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK) */
+#else /* CONFIG_ARCH_THREAD_STACK_ALLOCATOR */
+
+static int alloc_thread_stack_node(struct task_struct *tsk, int node)
+{
+	unsigned long *stack;
+
+	stack = arch_alloc_thread_stack_node(tsk, node);
+	tsk->stack = stack;
+	return stack ? 0 : -ENOMEM;
+}
+
+static void free_thread_stack(struct task_struct *tsk)
+{
+	arch_free_thread_stack(tsk);
+	tsk->stack = NULL;
+}
+
+#endif /* !CONFIG_ARCH_THREAD_STACK_ALLOCATOR */
+
+/* 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 */
+static struct kmem_cache *vm_area_cachep;
+
+/* SLAB cache for mm_struct structures (tsk->mm) */
+static struct kmem_cache *mm_cachep;
+
+#ifdef CONFIG_PER_VMA_LOCK
+
+/* SLAB cache for vm_area_struct.lock */
+static struct kmem_cache *vma_lock_cachep;
+
+static bool vma_lock_alloc(struct vm_area_struct *vma)
+{
+	vma->vm_lock = kmem_cache_alloc(vma_lock_cachep, GFP_KERNEL);
+	if (!vma->vm_lock)
+		return false;
+
+	init_rwsem(&vma->vm_lock->lock);
+	vma->vm_lock_seq = -1;
+
+	return true;
+}
+
+static inline void vma_lock_free(struct vm_area_struct *vma)
+{
+	kmem_cache_free(vma_lock_cachep, vma->vm_lock);
+}
+
+#else /* CONFIG_PER_VMA_LOCK */
+
+static inline bool vma_lock_alloc(struct vm_area_struct *vma) { return true; }
+static inline void vma_lock_free(struct vm_area_struct *vma) {}
+
+#endif /* CONFIG_PER_VMA_LOCK */
+
+struct vm_area_struct *vm_area_alloc(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+
+	vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
+	if (!vma)
+		return NULL;
+
+	vma_init(vma, mm);
+	if (!vma_lock_alloc(vma)) {
+		kmem_cache_free(vm_area_cachep, vma);
+		return NULL;
+	}
+
+	return vma;
+}
+
+struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
+{
+	struct vm_area_struct *new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
+
+	if (!new)
+		return NULL;
+
+	ASSERT_EXCLUSIVE_WRITER(orig->vm_flags);
+	ASSERT_EXCLUSIVE_WRITER(orig->vm_file);
+	/*
+	 * orig->shared.rb may be modified concurrently, but the clone
+	 * will be reinitialized.
+	 */
+	data_race(memcpy(new, orig, sizeof(*new)));
+	if (!vma_lock_alloc(new)) {
+		kmem_cache_free(vm_area_cachep, new);
+		return NULL;
+	}
+	INIT_LIST_HEAD(&new->anon_vma_chain);
+	vma_numab_state_init(new);
+	dup_anon_vma_name(orig, new);
+
+	return new;
+}
+
+void __vm_area_free(struct vm_area_struct *vma)
+{
+	vma_numab_state_free(vma);
+	free_anon_vma_name(vma);
+	vma_lock_free(vma);
+	kmem_cache_free(vm_area_cachep, vma);
+}
+
+#ifdef CONFIG_PER_VMA_LOCK
+static void vm_area_free_rcu_cb(struct rcu_head *head)
+{
+	struct vm_area_struct *vma = container_of(head, struct vm_area_struct,
+						  vm_rcu);
+
+	/* The vma should not be locked while being destroyed. */
+	VM_BUG_ON_VMA(rwsem_is_locked(&vma->vm_lock->lock), vma);
+	__vm_area_free(vma);
+}
+#endif
+
+void vm_area_free(struct vm_area_struct *vma)
+{
+#ifdef CONFIG_PER_VMA_LOCK
+	call_rcu(&vma->vm_rcu, vm_area_free_rcu_cb);
+#else
+	__vm_area_free(vma);
+#endif
+}
+
+static void account_kernel_stack(struct task_struct *tsk, int account)
+{
+	if (IS_ENABLED(CONFIG_VMAP_STACK)) {
+		struct vm_struct *vm = task_stack_vm_area(tsk);
+		int i;
+
+		for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++)
+			mod_lruvec_page_state(vm->pages[i], NR_KERNEL_STACK_KB,
+					      account * (PAGE_SIZE / 1024));
+	} else {
+		void *stack = task_stack_page(tsk);
+
+		/* All stack pages are in the same node. */
+		mod_lruvec_kmem_state(stack, NR_KERNEL_STACK_KB,
+				      account * (THREAD_SIZE / 1024));
+	}
+}
+
+void exit_task_stack_account(struct task_struct *tsk)
+{
+	account_kernel_stack(tsk, -1);
+
+	if (IS_ENABLED(CONFIG_VMAP_STACK)) {
+		struct vm_struct *vm;
+		int i;
+
+		vm = task_stack_vm_area(tsk);
+		for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++)
+			memcg_kmem_uncharge_page(vm->pages[i], 0);
+	}
+}
+
+static void release_task_stack(struct task_struct *tsk)
+{
+	if (WARN_ON(READ_ONCE(tsk->__state) != TASK_DEAD))
+		return;  /* Better to leak the stack than to free prematurely */
+
+	free_thread_stack(tsk);
+}
+
+#ifdef CONFIG_THREAD_INFO_IN_TASK
+void put_task_stack(struct task_struct *tsk)
+{
+	if (refcount_dec_and_test(&tsk->stack_refcount))
+		release_task_stack(tsk);
+}
+#endif
+
+void free_task(struct task_struct *tsk)
+{
+#ifdef CONFIG_SECCOMP
+	WARN_ON_ONCE(tsk->seccomp.filter);
+#endif
+	release_user_cpus_ptr(tsk);
+	scs_release(tsk);
+
+#ifndef CONFIG_THREAD_INFO_IN_TASK
+	/*
+	 * The task is finally done with both the stack and thread_info,
+	 * so free both.
+	 */
+	release_task_stack(tsk);
+#else
+	/*
+	 * If the task had a separate stack allocation, it should be gone
+	 * by now.
+	 */
+	WARN_ON_ONCE(refcount_read(&tsk->stack_refcount) != 0);
+#endif
+	rt_mutex_debug_task_free(tsk);
+	ftrace_graph_exit_task(tsk);
+	arch_release_task_struct(tsk);
+	if (tsk->flags & PF_KTHREAD)
+		free_kthread_struct(tsk);
+	bpf_task_storage_free(tsk);
+	free_task_struct(tsk);
+}
+EXPORT_SYMBOL(free_task);
+
+static void dup_mm_exe_file(struct mm_struct *mm, struct mm_struct *oldmm)
+{
+	struct file *exe_file;
+
+	exe_file = get_mm_exe_file(oldmm);
+	RCU_INIT_POINTER(mm->exe_file, exe_file);
+	/*
+	 * We depend on the oldmm having properly denied write access to the
+	 * exe_file already.
+	 */
+	if (exe_file && deny_write_access(exe_file))
+		pr_warn_once("deny_write_access() failed in %s\n", __func__);
+}
+
+#ifdef CONFIG_MMU
+static __latent_entropy int dup_mmap(struct mm_struct *mm,
+					struct mm_struct *oldmm)
+{
+	struct vm_area_struct *mpnt, *tmp;
+	int retval;
+	unsigned long charge = 0;
+	LIST_HEAD(uf);
+	VMA_ITERATOR(old_vmi, oldmm, 0);
+	VMA_ITERATOR(vmi, mm, 0);
+
+	uprobe_start_dup_mmap();
+	if (mmap_write_lock_killable(oldmm)) {
+		retval = -EINTR;
+		goto fail_uprobe_end;
+	}
+	flush_cache_dup_mm(oldmm);
+	uprobe_dup_mmap(oldmm, mm);
+	/*
+	 * Not linked in yet - no deadlock potential:
+	 */
+	mmap_write_lock_nested(mm, SINGLE_DEPTH_NESTING);
+
+	/* No ordering required: file already has been exposed. */
+	dup_mm_exe_file(mm, oldmm);
+
+	mm->total_vm = oldmm->total_vm;
+	mm->data_vm = oldmm->data_vm;
+	mm->exec_vm = oldmm->exec_vm;
+	mm->stack_vm = oldmm->stack_vm;
+
+	retval = ksm_fork(mm, oldmm);
+	if (retval)
+		goto out;
+	khugepaged_fork(mm, oldmm);
+
+	retval = vma_iter_bulk_alloc(&vmi, oldmm->map_count);
+	if (retval)
+		goto out;
+
+	mt_clear_in_rcu(vmi.mas.tree);
+	for_each_vma(old_vmi, mpnt) {
+		struct file *file;
+
+		vma_start_write(mpnt);
+		if (mpnt->vm_flags & VM_DONTCOPY) {
+			vm_stat_account(mm, mpnt->vm_flags, -vma_pages(mpnt));
+			continue;
+		}
+		charge = 0;
+		/*
+		 * Don't duplicate many vmas if we've been oom-killed (for
+		 * example)
+		 */
+		if (fatal_signal_pending(current)) {
+			retval = -EINTR;
+			goto loop_out;
+		}
+		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 = vm_area_dup(mpnt);
+		if (!tmp)
+			goto fail_nomem;
+		retval = vma_dup_policy(mpnt, tmp);
+		if (retval)
+			goto fail_nomem_policy;
+		tmp->vm_mm = mm;
+		retval = dup_userfaultfd(tmp, &uf);
+		if (retval)
+			goto fail_nomem_anon_vma_fork;
+		if (tmp->vm_flags & VM_WIPEONFORK) {
+			/*
+			 * VM_WIPEONFORK gets a clean slate in the child.
+			 * Don't prepare anon_vma until fault since we don't
+			 * copy page for current vma.
+			 */
+			tmp->anon_vma = NULL;
+		} else if (anon_vma_fork(tmp, mpnt))
+			goto fail_nomem_anon_vma_fork;
+		vm_flags_clear(tmp, VM_LOCKED_MASK);
+		file = tmp->vm_file;
+		if (file) {
+			struct address_space *mapping = file->f_mapping;
+
+			get_file(file);
+			i_mmap_lock_write(mapping);
+			if (tmp->vm_flags & VM_SHARED)
+				mapping_allow_writable(mapping);
+			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);
+		}
+
+		/*
+		 * Copy/update hugetlb private vma information.
+		 */
+		if (is_vm_hugetlb_page(tmp))
+			hugetlb_dup_vma_private(tmp);
+
+		/* Link the vma into the MT */
+		if (vma_iter_bulk_store(&vmi, tmp))
+			goto fail_nomem_vmi_store;
+
+		mm->map_count++;
+		if (!(tmp->vm_flags & VM_WIPEONFORK))
+			retval = copy_page_range(tmp, mpnt);
+
+		if (tmp->vm_ops && tmp->vm_ops->open)
+			tmp->vm_ops->open(tmp);
+
+		if (retval)
+			goto loop_out;
+	}
+	/* a new mm has just been created */
+	retval = arch_dup_mmap(oldmm, mm);
+loop_out:
+	vma_iter_free(&vmi);
+	if (!retval)
+		mt_set_in_rcu(vmi.mas.tree);
+out:
+	mmap_write_unlock(mm);
+	flush_tlb_mm(oldmm);
+	mmap_write_unlock(oldmm);
+	dup_userfaultfd_complete(&uf);
+fail_uprobe_end:
+	uprobe_end_dup_mmap();
+	return retval;
+
+fail_nomem_vmi_store:
+	unlink_anon_vmas(tmp);
+fail_nomem_anon_vma_fork:
+	mpol_put(vma_policy(tmp));
+fail_nomem_policy:
+	vm_area_free(tmp);
+fail_nomem:
+	retval = -ENOMEM;
+	vm_unacct_memory(charge);
+	goto loop_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)
+{
+	mmap_write_lock(oldmm);
+	dup_mm_exe_file(mm, oldmm);
+	mmap_write_unlock(oldmm);
+	return 0;
+}
+#define mm_alloc_pgd(mm)	(0)
+#define mm_free_pgd(mm)
+#endif /* CONFIG_MMU */
+
+static void check_mm(struct mm_struct *mm)
+{
+	int i;
+
+	BUILD_BUG_ON_MSG(ARRAY_SIZE(resident_page_types) != NR_MM_COUNTERS,
+			 "Please make sure 'struct resident_page_types[]' is updated as well");
+
+	for (i = 0; i < NR_MM_COUNTERS; i++) {
+		long x = percpu_counter_sum(&mm->rss_stat[i]);
+
+		if (unlikely(x))
+			pr_alert("BUG: Bad rss-counter state mm:%p type:%s val:%ld\n",
+				 mm, resident_page_types[i], x);
+	}
+
+	if (mm_pgtables_bytes(mm))
+		pr_alert("BUG: non-zero pgtables_bytes on freeing mm: %ld\n",
+				mm_pgtables_bytes(mm));
+
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
+	VM_BUG_ON_MM(mm->pmd_huge_pte, mm);
+#endif
+}
+
+#define allocate_mm()	(kmem_cache_alloc(mm_cachep, GFP_KERNEL))
+#define free_mm(mm)	(kmem_cache_free(mm_cachep, (mm)))
+
+static void do_check_lazy_tlb(void *arg)
+{
+	struct mm_struct *mm = arg;
+
+	WARN_ON_ONCE(current->active_mm == mm);
+}
+
+static void do_shoot_lazy_tlb(void *arg)
+{
+	struct mm_struct *mm = arg;
+
+	if (current->active_mm == mm) {
+		WARN_ON_ONCE(current->mm);
+		current->active_mm = &init_mm;
+		switch_mm(mm, &init_mm, current);
+	}
+}
+
+static void cleanup_lazy_tlbs(struct mm_struct *mm)
+{
+	if (!IS_ENABLED(CONFIG_MMU_LAZY_TLB_SHOOTDOWN)) {
+		/*
+		 * In this case, lazy tlb mms are refounted and would not reach
+		 * __mmdrop until all CPUs have switched away and mmdrop()ed.
+		 */
+		return;
+	}
+
+	/*
+	 * Lazy mm shootdown does not refcount "lazy tlb mm" usage, rather it
+	 * requires lazy mm users to switch to another mm when the refcount
+	 * drops to zero, before the mm is freed. This requires IPIs here to
+	 * switch kernel threads to init_mm.
+	 *
+	 * archs that use IPIs to flush TLBs can piggy-back that lazy tlb mm
+	 * switch with the final userspace teardown TLB flush which leaves the
+	 * mm lazy on this CPU but no others, reducing the need for additional
+	 * IPIs here. There are cases where a final IPI is still required here,
+	 * such as the final mmdrop being performed on a different CPU than the
+	 * one exiting, or kernel threads using the mm when userspace exits.
+	 *
+	 * IPI overheads have not found to be expensive, but they could be
+	 * reduced in a number of possible ways, for example (roughly
+	 * increasing order of complexity):
+	 * - The last lazy reference created by exit_mm() could instead switch
+	 *   to init_mm, however it's probable this will run on the same CPU
+	 *   immediately afterwards, so this may not reduce IPIs much.
+	 * - A batch of mms requiring IPIs could be gathered and freed at once.
+	 * - CPUs store active_mm where it can be remotely checked without a
+	 *   lock, to filter out false-positives in the cpumask.
+	 * - After mm_users or mm_count reaches zero, switching away from the
+	 *   mm could clear mm_cpumask to reduce some IPIs, perhaps together
+	 *   with some batching or delaying of the final IPIs.
+	 * - A delayed freeing and RCU-like quiescing sequence based on mm
+	 *   switching to avoid IPIs completely.
+	 */
+	on_each_cpu_mask(mm_cpumask(mm), do_shoot_lazy_tlb, (void *)mm, 1);
+	if (IS_ENABLED(CONFIG_DEBUG_VM_SHOOT_LAZIES))
+		on_each_cpu(do_check_lazy_tlb, (void *)mm, 1);
+}
+
+/*
+ * 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);
+	WARN_ON_ONCE(mm == current->mm);
+
+	/* Ensure no CPUs are using this as their lazy tlb mm */
+	cleanup_lazy_tlbs(mm);
+
+	WARN_ON_ONCE(mm == current->active_mm);
+	mm_free_pgd(mm);
+	destroy_context(mm);
+	mmu_notifier_subscriptions_destroy(mm);
+	check_mm(mm);
+	put_user_ns(mm->user_ns);
+	mm_pasid_drop(mm);
+	mm_destroy_cid(mm);
+	percpu_counter_destroy_many(mm->rss_stat, NR_MM_COUNTERS);
+
+	free_mm(mm);
+}
+EXPORT_SYMBOL_GPL(__mmdrop);
+
+static void mmdrop_async_fn(struct work_struct *work)
+{
+	struct mm_struct *mm;
+
+	mm = container_of(work, struct mm_struct, async_put_work);
+	__mmdrop(mm);
+}
+
+static void mmdrop_async(struct mm_struct *mm)
+{
+	if (unlikely(atomic_dec_and_test(&mm->mm_count))) {
+		INIT_WORK(&mm->async_put_work, mmdrop_async_fn);
+		schedule_work(&mm->async_put_work);
+	}
+}
+
+static inline void free_signal_struct(struct signal_struct *sig)
+{
+	taskstats_tgid_free(sig);
+	sched_autogroup_exit(sig);
+	/*
+	 * __mmdrop is not safe to call from softirq context on x86 due to
+	 * pgd_dtor so postpone it to the async context
+	 */
+	if (sig->oom_mm)
+		mmdrop_async(sig->oom_mm);
+	kmem_cache_free(signal_cachep, sig);
+}
+
+static inline void put_signal_struct(struct signal_struct *sig)
+{
+	if (refcount_dec_and_test(&sig->sigcnt))
+		free_signal_struct(sig);
+}
+
+void __put_task_struct(struct task_struct *tsk)
+{
+	WARN_ON(!tsk->exit_state);
+	WARN_ON(refcount_read(&tsk->usage));
+	WARN_ON(tsk == current);
+
+	io_uring_free(tsk);
+	cgroup_free(tsk);
+	task_numa_free(tsk, true);
+	security_task_free(tsk);
+	exit_creds(tsk);
+	delayacct_tsk_free(tsk);
+	put_signal_struct(tsk->signal);
+	sched_core_free(tsk);
+	free_task(tsk);
+}
+EXPORT_SYMBOL_GPL(__put_task_struct);
+
+void __put_task_struct_rcu_cb(struct rcu_head *rhp)
+{
+	struct task_struct *task = container_of(rhp, struct task_struct, rcu);
+
+	__put_task_struct(task);
+}
+EXPORT_SYMBOL_GPL(__put_task_struct_rcu_cb);
+
+void __init __weak arch_task_cache_init(void) { }
+
+/*
+ * set_max_threads
+ */
+static void set_max_threads(unsigned int max_threads_suggested)
+{
+	u64 threads;
+	unsigned long nr_pages = totalram_pages();
+
+	/*
+	 * The number of threads shall be limited such that the thread
+	 * structures may only consume a small part of the available memory.
+	 */
+	if (fls64(nr_pages) + fls64(PAGE_SIZE) > 64)
+		threads = MAX_THREADS;
+	else
+		threads = div64_u64((u64) nr_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);
+}
+
+#ifdef CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT
+/* Initialized by the architecture: */
+int arch_task_struct_size __read_mostly;
+#endif
+
+#ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
+static void task_struct_whitelist(unsigned long *offset, unsigned long *size)
+{
+	/* Fetch thread_struct whitelist for the architecture. */
+	arch_thread_struct_whitelist(offset, size);
+
+	/*
+	 * Handle zero-sized whitelist or empty thread_struct, otherwise
+	 * adjust offset to position of thread_struct in task_struct.
+	 */
+	if (unlikely(*size == 0))
+		*offset = 0;
+	else
+		*offset += offsetof(struct task_struct, thread);
+}
+#endif /* CONFIG_ARCH_TASK_STRUCT_ALLOCATOR */
+
+void __init fork_init(void)
+{
+	int i;
+#ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
+#ifndef ARCH_MIN_TASKALIGN
+#define ARCH_MIN_TASKALIGN	0
+#endif
+	int align = max_t(int, L1_CACHE_BYTES, ARCH_MIN_TASKALIGN);
+	unsigned long useroffset, usersize;
+
+	/* create a slab on which task_structs can be allocated */
+	task_struct_whitelist(&useroffset, &usersize);
+	task_struct_cachep = kmem_cache_create_usercopy("task_struct",
+			arch_task_struct_size, align,
+			SLAB_PANIC|SLAB_ACCOUNT,
+			useroffset, usersize, 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];
+
+	for (i = 0; i < UCOUNT_COUNTS; i++)
+		init_user_ns.ucount_max[i] = max_threads/2;
+
+	set_userns_rlimit_max(&init_user_ns, UCOUNT_RLIMIT_NPROC,      RLIM_INFINITY);
+	set_userns_rlimit_max(&init_user_ns, UCOUNT_RLIMIT_MSGQUEUE,   RLIM_INFINITY);
+	set_userns_rlimit_max(&init_user_ns, UCOUNT_RLIMIT_SIGPENDING, RLIM_INFINITY);
+	set_userns_rlimit_max(&init_user_ns, UCOUNT_RLIMIT_MEMLOCK,    RLIM_INFINITY);
+
+#ifdef CONFIG_VMAP_STACK
+	cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache",
+			  NULL, free_vm_stack_cache);
+#endif
+
+	scs_init();
+
+	lockdep_init_task(&init_task);
+	uprobes_init();
+}
+
+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, int node)
+{
+	struct task_struct *tsk;
+	int err;
+
+	if (node == NUMA_NO_NODE)
+		node = tsk_fork_get_node(orig);
+	tsk = alloc_task_struct_node(node);
+	if (!tsk)
+		return NULL;
+
+	err = arch_dup_task_struct(tsk, orig);
+	if (err)
+		goto free_tsk;
+
+	err = alloc_thread_stack_node(tsk, node);
+	if (err)
+		goto free_tsk;
+
+#ifdef CONFIG_THREAD_INFO_IN_TASK
+	refcount_set(&tsk->stack_refcount, 1);
+#endif
+	account_kernel_stack(tsk, 1);
+
+	err = scs_prepare(tsk, node);
+	if (err)
+		goto free_stack;
+
+#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);
+	clear_syscall_work_syscall_user_dispatch(tsk);
+
+#ifdef CONFIG_STACKPROTECTOR
+	tsk->stack_canary = get_random_canary();
+#endif
+	if (orig->cpus_ptr == &orig->cpus_mask)
+		tsk->cpus_ptr = &tsk->cpus_mask;
+	dup_user_cpus_ptr(tsk, orig, node);
+
+	/*
+	 * One for the user space visible state that goes away when reaped.
+	 * One for the scheduler.
+	 */
+	refcount_set(&tsk->rcu_users, 2);
+	/* One for the rcu users */
+	refcount_set(&tsk->usage, 1);
+#ifdef CONFIG_BLK_DEV_IO_TRACE
+	tsk->btrace_seq = 0;
+#endif
+	tsk->splice_pipe = NULL;
+	tsk->task_frag.page = NULL;
+	tsk->wake_q.next = NULL;
+	tsk->worker_private = NULL;
+
+	kcov_task_init(tsk);
+	kmsan_task_create(tsk);
+	kmap_local_fork(tsk);
+
+#ifdef CONFIG_FAULT_INJECTION
+	tsk->fail_nth = 0;
+#endif
+
+#ifdef CONFIG_BLK_CGROUP
+	tsk->throttle_disk = NULL;
+	tsk->use_memdelay = 0;
+#endif
+
+#ifdef CONFIG_IOMMU_SVA
+	tsk->pasid_activated = 0;
+#endif
+
+#ifdef CONFIG_MEMCG
+	tsk->active_memcg = NULL;
+#endif
+
+#ifdef CONFIG_CPU_SUP_INTEL
+	tsk->reported_split_lock = 0;
+#endif
+
+#ifdef CONFIG_SCHED_MM_CID
+	tsk->mm_cid = -1;
+	tsk->last_mm_cid = -1;
+	tsk->mm_cid_active = 0;
+	tsk->migrate_from_cpu = -1;
+#endif
+	return tsk;
+
+free_stack:
+	exit_task_stack_account(tsk);
+	free_thread_stack(tsk);
+free_tsk:
+	free_task_struct(tsk);
+	return NULL;
+}
+
+__cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
+
+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 __always_inline void mm_clear_owner(struct mm_struct *mm,
+					   struct task_struct *p)
+{
+#ifdef CONFIG_MEMCG
+	if (mm->owner == p)
+		WRITE_ONCE(mm->owner, NULL);
+#endif
+}
+
+static void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
+{
+#ifdef CONFIG_MEMCG
+	mm->owner = p;
+#endif
+}
+
+static void mm_init_uprobes_state(struct mm_struct *mm)
+{
+#ifdef CONFIG_UPROBES
+	mm->uprobes_state.xol_area = NULL;
+#endif
+}
+
+static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
+	struct user_namespace *user_ns)
+{
+	mt_init_flags(&mm->mm_mt, MM_MT_FLAGS);
+	mt_set_external_lock(&mm->mm_mt, &mm->mmap_lock);
+	atomic_set(&mm->mm_users, 1);
+	atomic_set(&mm->mm_count, 1);
+	seqcount_init(&mm->write_protect_seq);
+	mmap_init_lock(mm);
+	INIT_LIST_HEAD(&mm->mmlist);
+#ifdef CONFIG_PER_VMA_LOCK
+	mm->mm_lock_seq = 0;
+#endif
+	mm_pgtables_bytes_init(mm);
+	mm->map_count = 0;
+	mm->locked_vm = 0;
+	atomic64_set(&mm->pinned_vm, 0);
+	memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
+	spin_lock_init(&mm->page_table_lock);
+	spin_lock_init(&mm->arg_lock);
+	mm_init_cpumask(mm);
+	mm_init_aio(mm);
+	mm_init_owner(mm, p);
+	mm_pasid_init(mm);
+	RCU_INIT_POINTER(mm->exe_file, NULL);
+	mmu_notifier_subscriptions_init(mm);
+	init_tlb_flush_pending(mm);
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
+	mm->pmd_huge_pte = NULL;
+#endif
+	mm_init_uprobes_state(mm);
+	hugetlb_count_init(mm);
+
+	if (current->mm) {
+		mm->flags = mmf_init_flags(current->mm->flags);
+		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;
+
+	if (mm_alloc_cid(mm))
+		goto fail_cid;
+
+	if (percpu_counter_init_many(mm->rss_stat, 0, GFP_KERNEL_ACCOUNT,
+				     NR_MM_COUNTERS))
+		goto fail_pcpu;
+
+	mm->user_ns = get_user_ns(user_ns);
+	lru_gen_init_mm(mm);
+	return mm;
+
+fail_pcpu:
+	mm_destroy_cid(mm);
+fail_cid:
+	destroy_context(mm);
+fail_nocontext:
+	mm_free_pgd(mm);
+fail_nopgd:
+	free_mm(mm);
+	return NULL;
+}
+
+/*
+ * Allocate and initialize an mm_struct.
+ */
+struct mm_struct *mm_alloc(void)
+{
+	struct mm_struct *mm;
+
+	mm = allocate_mm();
+	if (!mm)
+		return NULL;
+
+	memset(mm, 0, sizeof(*mm));
+	return mm_init(mm, current, current_user_ns());
+}
+
+static inline void __mmput(struct mm_struct *mm)
+{
+	VM_BUG_ON(atomic_read(&mm->mm_users));
+
+	uprobe_clear_state(mm);
+	exit_aio(mm);
+	ksm_exit(mm);
+	khugepaged_exit(mm); /* must run before exit_mmap */
+	exit_mmap(mm);
+	mm_put_huge_zero_page(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);
+	lru_gen_del_mm(mm);
+	mmdrop(mm);
+}
+
+/*
+ * 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))
+		__mmput(mm);
+}
+EXPORT_SYMBOL_GPL(mmput);
+
+#ifdef CONFIG_MMU
+static void mmput_async_fn(struct work_struct *work)
+{
+	struct mm_struct *mm = container_of(work, struct mm_struct,
+					    async_put_work);
+
+	__mmput(mm);
+}
+
+void mmput_async(struct mm_struct *mm)
+{
+	if (atomic_dec_and_test(&mm->mm_users)) {
+		INIT_WORK(&mm->async_put_work, mmput_async_fn);
+		schedule_work(&mm->async_put_work);
+	}
+}
+EXPORT_SYMBOL_GPL(mmput_async);
+#endif
+
+/**
+ * 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 it happens before
+ * the new mm is made visible to anyone.
+ *
+ * Can only fail if new_exe_file != NULL.
+ */
+int 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) {
+		/*
+		 * We expect the caller (i.e., sys_execve) to already denied
+		 * write access, so this is unlikely to fail.
+		 */
+		if (unlikely(deny_write_access(new_exe_file)))
+			return -EACCES;
+		get_file(new_exe_file);
+	}
+	rcu_assign_pointer(mm->exe_file, new_exe_file);
+	if (old_exe_file) {
+		allow_write_access(old_exe_file);
+		fput(old_exe_file);
+	}
+	return 0;
+}
+
+/**
+ * replace_mm_exe_file - replace a reference to the mm's executable file
+ *
+ * This changes mm's executable file (shown as symlink /proc/[pid]/exe).
+ *
+ * Main user is sys_prctl(PR_SET_MM_MAP/EXE_FILE).
+ */
+int replace_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
+{
+	struct vm_area_struct *vma;
+	struct file *old_exe_file;
+	int ret = 0;
+
+	/* Forbid mm->exe_file change if old file still mapped. */
+	old_exe_file = get_mm_exe_file(mm);
+	if (old_exe_file) {
+		VMA_ITERATOR(vmi, mm, 0);
+		mmap_read_lock(mm);
+		for_each_vma(vmi, vma) {
+			if (!vma->vm_file)
+				continue;
+			if (path_equal(&vma->vm_file->f_path,
+				       &old_exe_file->f_path)) {
+				ret = -EBUSY;
+				break;
+			}
+		}
+		mmap_read_unlock(mm);
+		fput(old_exe_file);
+		if (ret)
+			return ret;
+	}
+
+	ret = deny_write_access(new_exe_file);
+	if (ret)
+		return -EACCES;
+	get_file(new_exe_file);
+
+	/* set the new file */
+	mmap_write_lock(mm);
+	old_exe_file = rcu_dereference_raw(mm->exe_file);
+	rcu_assign_pointer(mm->exe_file, new_exe_file);
+	mmap_write_unlock(mm);
+
+	if (old_exe_file) {
+		allow_write_access(old_exe_file);
+		fput(old_exe_file);
+	}
+	return 0;
+}
+
+/**
+ * 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;
+}
+
+/**
+ * get_task_exe_file - acquire a reference to the task's executable file
+ *
+ * Returns %NULL if task's mm (if any) has no associated executable file or
+ * this is a kernel thread with borrowed mm (see the comment above get_task_mm).
+ * User must release file via fput().
+ */
+struct file *get_task_exe_file(struct task_struct *task)
+{
+	struct file *exe_file = NULL;
+	struct mm_struct *mm;
+
+	task_lock(task);
+	mm = task->mm;
+	if (mm) {
+		if (!(task->flags & PF_KTHREAD))
+			exe_file = get_mm_exe_file(mm);
+	}
+	task_unlock(task);
+	return 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
+			mmget(mm);
+	}
+	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 =  down_read_killable(&task->signal->exec_update_lock);
+	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);
+	}
+	up_read(&task->signal->exec_update_lock);
+
+	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)
+{
+	unsigned int state = TASK_UNINTERRUPTIBLE|TASK_KILLABLE|TASK_FREEZABLE;
+	int killed;
+
+	cgroup_enter_frozen();
+	killed = wait_for_completion_state(vfork, state);
+	cgroup_leave_frozen(false);
+
+	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
+ */
+static void mm_release(struct task_struct *tsk, struct mm_struct *mm)
+{
+	uprobe_free_utask(tsk);
+
+	/* Get rid of any cached register state */
+	deactivate_mm(tsk, mm);
+
+	/*
+	 * Signal userspace if we're not exiting with a core dump
+	 * because we want to leave the value intact for debugging
+	 * purposes.
+	 */
+	if (tsk->clear_child_tid) {
+		if (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);
+			do_futex(tsk->clear_child_tid, FUTEX_WAKE,
+					1, NULL, NULL, 0, 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);
+}
+
+void exit_mm_release(struct task_struct *tsk, struct mm_struct *mm)
+{
+	futex_exit_release(tsk);
+	mm_release(tsk, mm);
+}
+
+void exec_mm_release(struct task_struct *tsk, struct mm_struct *mm)
+{
+	futex_exec_release(tsk);
+	mm_release(tsk, mm);
+}
+
+/**
+ * dup_mm() - duplicates an existing mm structure
+ * @tsk: the task_struct with which the new mm will be associated.
+ * @oldmm: the mm to duplicate.
+ *
+ * Allocates a new mm structure and duplicates the provided @oldmm structure
+ * content into it.
+ *
+ * Return: the duplicated mm or NULL on failure.
+ */
+static struct mm_struct *dup_mm(struct task_struct *tsk,
+				struct mm_struct *oldmm)
+{
+	struct mm_struct *mm;
+	int err;
+
+	mm = allocate_mm();
+	if (!mm)
+		goto fail_nomem;
+
+	memcpy(mm, oldmm, sizeof(*mm));
+
+	if (!mm_init(mm, tsk, mm->user_ns))
+		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;
+	mm_init_owner(mm, NULL);
+	mmput(mm);
+
+fail_nomem:
+	return NULL;
+}
+
+static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
+{
+	struct mm_struct *mm, *oldmm;
+
+	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;
+	tsk->last_switch_time = 0;
+#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;
+
+	if (clone_flags & CLONE_VM) {
+		mmget(oldmm);
+		mm = oldmm;
+	} else {
+		mm = dup_mm(tsk, current->mm);
+		if (!mm)
+			return -ENOMEM;
+	}
+
+	tsk->mm = mm;
+	tsk->active_mm = mm;
+	sched_mm_cid_fork(tsk);
+	return 0;
+}
+
+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,
+		      int no_files)
+{
+	struct files_struct *oldf, *newf;
+	int error = 0;
+
+	/*
+	 * A background process may not have any files ...
+	 */
+	oldf = current->files;
+	if (!oldf)
+		goto out;
+
+	if (no_files) {
+		tsk->files = NULL;
+		goto out;
+	}
+
+	if (clone_flags & CLONE_FILES) {
+		atomic_inc(&oldf->count);
+		goto out;
+	}
+
+	newf = dup_fd(oldf, NR_OPEN_MAX, &error);
+	if (!newf)
+		goto out;
+
+	tsk->files = newf;
+	error = 0;
+out:
+	return error;
+}
+
+static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
+{
+	struct sighand_struct *sig;
+
+	if (clone_flags & CLONE_SIGHAND) {
+		refcount_inc(&current->sighand->count);
+		return 0;
+	}
+	sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
+	RCU_INIT_POINTER(tsk->sighand, sig);
+	if (!sig)
+		return -ENOMEM;
+
+	refcount_set(&sig->count, 1);
+	spin_lock_irq(&current->sighand->siglock);
+	memcpy(sig->action, current->sighand->action, sizeof(sig->action));
+	spin_unlock_irq(&current->sighand->siglock);
+
+	/* Reset all signal handler not set to SIG_IGN to SIG_DFL. */
+	if (clone_flags & CLONE_CLEAR_SIGHAND)
+		flush_signal_handlers(tsk, 0);
+
+	return 0;
+}
+
+void __cleanup_sighand(struct sighand_struct *sighand)
+{
+	if (refcount_dec_and_test(&sighand->count)) {
+		signalfd_cleanup(sighand);
+		/*
+		 * sighand_cachep is SLAB_TYPESAFE_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)
+{
+	struct posix_cputimers *pct = &sig->posix_cputimers;
+	unsigned long cpu_limit;
+
+	cpu_limit = READ_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
+	posix_cputimers_group_init(pct, cpu_limit);
+}
+
+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;
+	sig->quick_threads = 1;
+	atomic_set(&sig->live, 1);
+	refcount_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_HLIST_HEAD(&sig->multiprocess);
+	seqlock_init(&sig->stats_lock);
+	prev_cputime_init(&sig->prev_cputime);
+
+#ifdef CONFIG_POSIX_TIMERS
+	INIT_LIST_HEAD(&sig->posix_timers);
+	hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	sig->real_timer.function = it_real_fn;
+#endif
+
+	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);
+
+	sig->oom_score_adj = current->signal->oom_score_adj;
+	sig->oom_score_adj_min = current->signal->oom_score_adj_min;
+
+	mutex_init(&sig->cred_guard_mutex);
+	init_rwsem(&sig->exec_update_lock);
+
+	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_task_syscall_work(p, 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_CACHED;
+	p->pi_top_task = NULL;
+	p->pi_blocked_on = NULL;
+#endif
+}
+
+static inline void init_task_pid_links(struct task_struct *task)
+{
+	enum pid_type type;
+
+	for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type)
+		INIT_HLIST_NODE(&task->pid_links[type]);
+}
+
+static inline void
+init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
+{
+	if (type == PIDTYPE_PID)
+		task->thread_pid = pid;
+	else
+		task->signal->pids[type] = pid;
+}
+
+static inline void rcu_copy_process(struct task_struct *p)
+{
+#ifdef CONFIG_PREEMPT_RCU
+	p->rcu_read_lock_nesting = 0;
+	p->rcu_read_unlock_special.s = 0;
+	p->rcu_blocked_node = NULL;
+	INIT_LIST_HEAD(&p->rcu_node_entry);
+#endif /* #ifdef CONFIG_PREEMPT_RCU */
+#ifdef CONFIG_TASKS_RCU
+	p->rcu_tasks_holdout = false;
+	INIT_LIST_HEAD(&p->rcu_tasks_holdout_list);
+	p->rcu_tasks_idle_cpu = -1;
+#endif /* #ifdef CONFIG_TASKS_RCU */
+#ifdef CONFIG_TASKS_TRACE_RCU
+	p->trc_reader_nesting = 0;
+	p->trc_reader_special.s = 0;
+	INIT_LIST_HEAD(&p->trc_holdout_list);
+	INIT_LIST_HEAD(&p->trc_blkd_node);
+#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
+}
+
+struct pid *pidfd_pid(const struct file *file)
+{
+	if (file->f_op == &pidfd_fops)
+		return file->private_data;
+
+	return ERR_PTR(-EBADF);
+}
+
+static int pidfd_release(struct inode *inode, struct file *file)
+{
+	struct pid *pid = file->private_data;
+
+	file->private_data = NULL;
+	put_pid(pid);
+	return 0;
+}
+
+#ifdef CONFIG_PROC_FS
+/**
+ * pidfd_show_fdinfo - print information about a pidfd
+ * @m: proc fdinfo file
+ * @f: file referencing a pidfd
+ *
+ * Pid:
+ * This function will print the pid that a given pidfd refers to in the
+ * pid namespace of the procfs instance.
+ * If the pid namespace of the process is not a descendant of the pid
+ * namespace of the procfs instance 0 will be shown as its pid. This is
+ * similar to calling getppid() on a process whose parent is outside of
+ * its pid namespace.
+ *
+ * NSpid:
+ * If pid namespaces are supported then this function will also print
+ * the pid of a given pidfd refers to for all descendant pid namespaces
+ * starting from the current pid namespace of the instance, i.e. the
+ * Pid field and the first entry in the NSpid field will be identical.
+ * If the pid namespace of the process is not a descendant of the pid
+ * namespace of the procfs instance 0 will be shown as its first NSpid
+ * entry and no others will be shown.
+ * Note that this differs from the Pid and NSpid fields in
+ * /proc/<pid>/status where Pid and NSpid are always shown relative to
+ * the  pid namespace of the procfs instance. The difference becomes
+ * obvious when sending around a pidfd between pid namespaces from a
+ * different branch of the tree, i.e. where no ancestral relation is
+ * present between the pid namespaces:
+ * - create two new pid namespaces ns1 and ns2 in the initial pid
+ *   namespace (also take care to create new mount namespaces in the
+ *   new pid namespace and mount procfs)
+ * - create a process with a pidfd in ns1
+ * - send pidfd from ns1 to ns2
+ * - read /proc/self/fdinfo/<pidfd> and observe that both Pid and NSpid
+ *   have exactly one entry, which is 0
+ */
+static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
+{
+	struct pid *pid = f->private_data;
+	struct pid_namespace *ns;
+	pid_t nr = -1;
+
+	if (likely(pid_has_task(pid, PIDTYPE_PID))) {
+		ns = proc_pid_ns(file_inode(m->file)->i_sb);
+		nr = pid_nr_ns(pid, ns);
+	}
+
+	seq_put_decimal_ll(m, "Pid:\t", nr);
+
+#ifdef CONFIG_PID_NS
+	seq_put_decimal_ll(m, "\nNSpid:\t", nr);
+	if (nr > 0) {
+		int i;
+
+		/* If nr is non-zero it means that 'pid' is valid and that
+		 * ns, i.e. the pid namespace associated with the procfs
+		 * instance, is in the pid namespace hierarchy of pid.
+		 * Start at one below the already printed level.
+		 */
+		for (i = ns->level + 1; i <= pid->level; i++)
+			seq_put_decimal_ll(m, "\t", pid->numbers[i].nr);
+	}
+#endif
+	seq_putc(m, '\n');
+}
+#endif
+
+/*
+ * Poll support for process exit notification.
+ */
+static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
+{
+	struct pid *pid = file->private_data;
+	__poll_t poll_flags = 0;
+
+	poll_wait(file, &pid->wait_pidfd, pts);
+
+	/*
+	 * Inform pollers only when the whole thread group exits.
+	 * If the thread group leader exits before all other threads in the
+	 * group, then poll(2) should block, similar to the wait(2) family.
+	 */
+	if (thread_group_exited(pid))
+		poll_flags = EPOLLIN | EPOLLRDNORM;
+
+	return poll_flags;
+}
+
+const struct file_operations pidfd_fops = {
+	.release = pidfd_release,
+	.poll = pidfd_poll,
+#ifdef CONFIG_PROC_FS
+	.show_fdinfo = pidfd_show_fdinfo,
+#endif
+};
+
+/**
+ * __pidfd_prepare - allocate a new pidfd_file and reserve a pidfd
+ * @pid:   the struct pid for which to create a pidfd
+ * @flags: flags of the new @pidfd
+ * @pidfd: the pidfd to return
+ *
+ * Allocate a new file that stashes @pid and reserve a new pidfd number in the
+ * caller's file descriptor table. The pidfd is reserved but not installed yet.
+
+ * The helper doesn't perform checks on @pid which makes it useful for pidfds
+ * created via CLONE_PIDFD where @pid has no task attached when the pidfd and
+ * pidfd file are prepared.
+ *
+ * If this function returns successfully the caller is responsible to either
+ * call fd_install() passing the returned pidfd and pidfd file as arguments in
+ * order to install the pidfd into its file descriptor table or they must use
+ * put_unused_fd() and fput() on the returned pidfd and pidfd file
+ * respectively.
+ *
+ * This function is useful when a pidfd must already be reserved but there
+ * might still be points of failure afterwards and the caller wants to ensure
+ * that no pidfd is leaked into its file descriptor table.
+ *
+ * Return: On success, a reserved pidfd is returned from the function and a new
+ *         pidfd file is returned in the last argument to the function. On
+ *         error, a negative error code is returned from the function and the
+ *         last argument remains unchanged.
+ */
+static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)
+{
+	int pidfd;
+	struct file *pidfd_file;
+
+	if (flags & ~(O_NONBLOCK | O_RDWR | O_CLOEXEC))
+		return -EINVAL;
+
+	pidfd = get_unused_fd_flags(O_RDWR | O_CLOEXEC);
+	if (pidfd < 0)
+		return pidfd;
+
+	pidfd_file = anon_inode_getfile("[pidfd]", &pidfd_fops, pid,
+					flags | O_RDWR | O_CLOEXEC);
+	if (IS_ERR(pidfd_file)) {
+		put_unused_fd(pidfd);
+		return PTR_ERR(pidfd_file);
+	}
+	get_pid(pid); /* held by pidfd_file now */
+	*ret = pidfd_file;
+	return pidfd;
+}
+
+/**
+ * pidfd_prepare - allocate a new pidfd_file and reserve a pidfd
+ * @pid:   the struct pid for which to create a pidfd
+ * @flags: flags of the new @pidfd
+ * @pidfd: the pidfd to return
+ *
+ * Allocate a new file that stashes @pid and reserve a new pidfd number in the
+ * caller's file descriptor table. The pidfd is reserved but not installed yet.
+ *
+ * The helper verifies that @pid is used as a thread group leader.
+ *
+ * If this function returns successfully the caller is responsible to either
+ * call fd_install() passing the returned pidfd and pidfd file as arguments in
+ * order to install the pidfd into its file descriptor table or they must use
+ * put_unused_fd() and fput() on the returned pidfd and pidfd file
+ * respectively.
+ *
+ * This function is useful when a pidfd must already be reserved but there
+ * might still be points of failure afterwards and the caller wants to ensure
+ * that no pidfd is leaked into its file descriptor table.
+ *
+ * Return: On success, a reserved pidfd is returned from the function and a new
+ *         pidfd file is returned in the last argument to the function. On
+ *         error, a negative error code is returned from the function and the
+ *         last argument remains unchanged.
+ */
+int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)
+{
+	if (!pid || !pid_has_task(pid, PIDTYPE_TGID))
+		return -EINVAL;
+
+	return __pidfd_prepare(pid, flags, ret);
+}
+
+static void __delayed_free_task(struct rcu_head *rhp)
+{
+	struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);
+
+	free_task(tsk);
+}
+
+static __always_inline void delayed_free_task(struct task_struct *tsk)
+{
+	if (IS_ENABLED(CONFIG_MEMCG))
+		call_rcu(&tsk->rcu, __delayed_free_task);
+	else
+		free_task(tsk);
+}
+
+static void copy_oom_score_adj(u64 clone_flags, struct task_struct *tsk)
+{
+	/* Skip if kernel thread */
+	if (!tsk->mm)
+		return;
+
+	/* Skip if spawning a thread or using vfork */
+	if ((clone_flags & (CLONE_VM | CLONE_THREAD | CLONE_VFORK)) != CLONE_VM)
+		return;
+
+	/* We need to synchronize with __set_oom_adj */
+	mutex_lock(&oom_adj_mutex);
+	set_bit(MMF_MULTIPROCESS, &tsk->mm->flags);
+	/* Update the values in case they were changed after copy_signal */
+	tsk->signal->oom_score_adj = current->signal->oom_score_adj;
+	tsk->signal->oom_score_adj_min = current->signal->oom_score_adj_min;
+	mutex_unlock(&oom_adj_mutex);
+}
+
+#ifdef CONFIG_RV
+static void rv_task_fork(struct task_struct *p)
+{
+	int i;
+
+	for (i = 0; i < RV_PER_TASK_MONITORS; i++)
+		p->rv[i].da_mon.monitoring = false;
+}
+#else
+#define rv_task_fork(p) do {} while (0)
+#endif
+
+/*
+ * 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.
+ */
+__latent_entropy struct task_struct *copy_process(
+					struct pid *pid,
+					int trace,
+					int node,
+					struct kernel_clone_args *args)
+{
+	int pidfd = -1, retval;
+	struct task_struct *p;
+	struct multiprocess_signals delayed;
+	struct file *pidfile = NULL;
+	const u64 clone_flags = args->flags;
+	struct nsproxy *nsp = current->nsproxy;
+
+	/*
+	 * Don't allow sharing the root directory with processes in a different
+	 * namespace
+	 */
+	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 with the forking task.
+	 */
+	if (clone_flags & CLONE_THREAD) {
+		if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
+		    (task_active_pid_ns(current) != nsp->pid_ns_for_children))
+			return ERR_PTR(-EINVAL);
+	}
+
+	if (clone_flags & CLONE_PIDFD) {
+		/*
+		 * - CLONE_DETACHED is blocked so that we can potentially
+		 *   reuse it later for CLONE_PIDFD.
+		 * - CLONE_THREAD is blocked until someone really needs it.
+		 */
+		if (clone_flags & (CLONE_DETACHED | CLONE_THREAD))
+			return ERR_PTR(-EINVAL);
+	}
+
+	/*
+	 * Force any signals received before this point to be delivered
+	 * before the fork happens.  Collect up signals sent to multiple
+	 * processes that happen during the fork and delay them so that
+	 * they appear to happen after the fork.
+	 */
+	sigemptyset(&delayed.signal);
+	INIT_HLIST_NODE(&delayed.node);
+
+	spin_lock_irq(&current->sighand->siglock);
+	if (!(clone_flags & CLONE_THREAD))
+		hlist_add_head(&delayed.node, &current->signal->multiprocess);
+	recalc_sigpending();
+	spin_unlock_irq(&current->sighand->siglock);
+	retval = -ERESTARTNOINTR;
+	if (task_sigpending(current))
+		goto fork_out;
+
+	retval = -ENOMEM;
+	p = dup_task_struct(current, node);
+	if (!p)
+		goto fork_out;
+	p->flags &= ~PF_KTHREAD;
+	if (args->kthread)
+		p->flags |= PF_KTHREAD;
+	if (args->user_worker) {
+		/*
+		 * Mark us a user worker, and block any signal that isn't
+		 * fatal or STOP
+		 */
+		p->flags |= PF_USER_WORKER;
+		siginitsetinv(&p->blocked, sigmask(SIGKILL)|sigmask(SIGSTOP));
+	}
+	if (args->io_thread)
+		p->flags |= PF_IO_WORKER;
+
+	if (args->name)
+		strscpy_pad(p->comm, args->name, sizeof(p->comm));
+
+	p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? args->child_tid : NULL;
+	/*
+	 * Clear TID on mm_release()?
+	 */
+	p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? args->child_tid : NULL;
+
+	ftrace_graph_init_task(p);
+
+	rt_mutex_init_task(p);
+
+	lockdep_assert_irqs_enabled();
+#ifdef CONFIG_PROVE_LOCKING
+	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
+#endif
+	retval = copy_creds(p, clone_flags);
+	if (retval < 0)
+		goto bad_fork_free;
+
+	retval = -EAGAIN;
+	if (is_rlimit_overlimit(task_ucounts(p), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) {
+		if (p->real_cred->user != INIT_USER &&
+		    !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
+			goto bad_fork_cleanup_count;
+	}
+	current->flags &= ~PF_NPROC_EXCEEDED;
+
+	/*
+	 * 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 (data_race(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 | PF_IDLE | PF_NO_SETAFFINITY);
+	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;
+#ifdef CONFIG_ARCH_HAS_SCALED_CPUTIME
+	p->utimescaled = p->stimescaled = 0;
+#endif
+	prev_cputime_init(&p->prev_cputime);
+
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
+	seqcount_init(&p->vtime.seqcount);
+	p->vtime.starttime = 0;
+	p->vtime.state = VTIME_INACTIVE;
+#endif
+
+#ifdef CONFIG_IO_URING
+	p->io_uring = NULL;
+#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;
+
+#ifdef CONFIG_PSI
+	p->psi_flags = 0;
+#endif
+
+	task_io_accounting_init(&p->ioac);
+	acct_clear_integrals(p);
+
+	posix_cputimers_init(&p->posix_cputimers);
+
+	p->io_context = NULL;
+	audit_set_context(p, NULL);
+	cgroup_fork(p);
+	if (args->kthread) {
+		if (!set_kthread_struct(p))
+			goto bad_fork_cleanup_delayacct;
+	}
+#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_delayacct;
+	}
+#endif
+#ifdef CONFIG_CPUSETS
+	p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
+	p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
+	seqcount_spinlock_init(&p->mems_allowed_seq, &p->alloc_lock);
+#endif
+#ifdef CONFIG_TRACE_IRQFLAGS
+	memset(&p->irqtrace, 0, sizeof(p->irqtrace));
+	p->irqtrace.hardirq_disable_ip	= _THIS_IP_;
+	p->irqtrace.softirq_enable_ip	= _THIS_IP_;
+	p->softirqs_enabled		= 1;
+	p->softirq_context		= 0;
+#endif
+
+	p->pagefault_disabled = 0;
+
+#ifdef CONFIG_LOCKDEP
+	lockdep_init_task(p);
+#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
+#ifdef CONFIG_BPF_SYSCALL
+	RCU_INIT_POINTER(p->bpf_storage, NULL);
+	p->bpf_ctx = NULL;
+#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, clone_flags);
+	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 = security_task_alloc(p, clone_flags);
+	if (retval)
+		goto bad_fork_cleanup_audit;
+	retval = copy_semundo(clone_flags, p);
+	if (retval)
+		goto bad_fork_cleanup_security;
+	retval = copy_files(clone_flags, p, args->no_files);
+	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(p, args);
+	if (retval)
+		goto bad_fork_cleanup_io;
+
+	stackleak_task_init(p);
+
+	if (pid != &init_struct_pid) {
+		pid = alloc_pid(p->nsproxy->pid_ns_for_children, args->set_tid,
+				args->set_tid_size);
+		if (IS_ERR(pid)) {
+			retval = PTR_ERR(pid);
+			goto bad_fork_cleanup_thread;
+		}
+	}
+
+	/*
+	 * This has to happen after we've potentially unshared the file
+	 * descriptor table (so that the pidfd doesn't leak into the child
+	 * if the fd table isn't shared).
+	 */
+	if (clone_flags & CLONE_PIDFD) {
+		/* Note that no task has been attached to @pid yet. */
+		retval = __pidfd_prepare(pid, O_RDWR | O_CLOEXEC, &pidfile);
+		if (retval < 0)
+			goto bad_fork_free_pid;
+		pidfd = retval;
+
+		retval = put_user(pidfd, args->pidfd);
+		if (retval)
+			goto bad_fork_put_pidfd;
+	}
+
+#ifdef CONFIG_BLOCK
+	p->plug = NULL;
+#endif
+	futex_init_task(p);
+
+	/*
+	 * sigaltstack should be cleared when sharing the same VM
+	 */
+	if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
+		sas_ss_reset(p);
+
+	/*
+	 * Syscall tracing and stepping should be turned off in the
+	 * child regardless of CLONE_PTRACE.
+	 */
+	user_disable_single_step(p);
+	clear_task_syscall_work(p, SYSCALL_TRACE);
+#if defined(CONFIG_GENERIC_ENTRY) || defined(TIF_SYSCALL_EMU)
+	clear_task_syscall_work(p, SYSCALL_EMU);
+#endif
+	clear_tsk_latency_tracing(p);
+
+	/* ok, now we should be set up.. */
+	p->pid = pid_nr(pid);
+	if (clone_flags & CLONE_THREAD) {
+		p->group_leader = current->group_leader;
+		p->tgid = current->tgid;
+	} else {
+		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;
+	clear_posix_cputimers_work(p);
+
+#ifdef CONFIG_KRETPROBES
+	p->kretprobe_instances.first = NULL;
+#endif
+#ifdef CONFIG_RETHOOK
+	p->rethooks.first = NULL;
+#endif
+
+	/*
+	 * Ensure that the cgroup subsystem policies allow the new process to be
+	 * forked. It should be noted that the new process's css_set can be changed
+	 * between here and cgroup_post_fork() if an organisation operation is in
+	 * progress.
+	 */
+	retval = cgroup_can_fork(p, args);
+	if (retval)
+		goto bad_fork_put_pidfd;
+
+	/*
+	 * Now that the cgroups are pinned, re-clone the parent cgroup and put
+	 * the new task on the correct runqueue. All this *before* the task
+	 * becomes visible.
+	 *
+	 * This isn't part of ->can_fork() because while the re-cloning is
+	 * cgroup specific, it unconditionally needs to place the task on a
+	 * runqueue.
+	 */
+	sched_cgroup_fork(p, args);
+
+	/*
+	 * From this point on we must avoid any synchronous user-space
+	 * communication until we take the tasklist-lock. In particular, we do
+	 * not want user-space to be able to predict the process start-time by
+	 * stalling fork(2) after we recorded the start_time but before it is
+	 * visible to the system.
+	 */
+
+	p->start_time = ktime_get_ns();
+	p->start_boottime = ktime_get_boottime_ns();
+
+	/*
+	 * 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;
+		if (clone_flags & CLONE_THREAD)
+			p->exit_signal = -1;
+		else
+			p->exit_signal = current->group_leader->exit_signal;
+	} else {
+		p->real_parent = current;
+		p->parent_exec_id = current->self_exec_id;
+		p->exit_signal = args->exit_signal;
+	}
+
+	klp_copy_process(p);
+
+	sched_core_fork(p);
+
+	spin_lock(&current->sighand->siglock);
+
+	rv_task_fork(p);
+
+	rseq_fork(p, clone_flags);
+
+	/* Don't start children in a dying pid namespace */
+	if (unlikely(!(ns_of_pid(pid)->pid_allocated & PIDNS_ADDING))) {
+		retval = -ENOMEM;
+		goto bad_fork_cancel_cgroup;
+	}
+
+	/* Let kill terminate clone/fork in the middle */
+	if (fatal_signal_pending(current)) {
+		retval = -EINTR;
+		goto bad_fork_cancel_cgroup;
+	}
+
+	/* No more failure paths after this point. */
+
+	/*
+	 * Copy seccomp details explicitly here, in case they were changed
+	 * before holding sighand lock.
+	 */
+	copy_seccomp(p);
+
+	init_task_pid_links(p);
+	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_TGID, pid);
+			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->shared_pending.signal = delayed.signal;
+			p->signal->tty = tty_kref_get(current->signal->tty);
+			/*
+			 * Inherit has_child_subreaper flag under the same
+			 * tasklist_lock with adding child to the process tree
+			 * for propagate_has_child_subreaper optimization.
+			 */
+			p->signal->has_child_subreaper = p->real_parent->signal->has_child_subreaper ||
+							 p->real_parent->signal->is_child_subreaper;
+			list_add_tail(&p->sibling, &p->real_parent->children);
+			list_add_tail_rcu(&p->tasks, &init_task.tasks);
+			attach_pid(p, PIDTYPE_TGID);
+			attach_pid(p, PIDTYPE_PGID);
+			attach_pid(p, PIDTYPE_SID);
+			__this_cpu_inc(process_counts);
+		} else {
+			current->signal->nr_threads++;
+			current->signal->quick_threads++;
+			atomic_inc(&current->signal->live);
+			refcount_inc(&current->signal->sigcnt);
+			task_join_group_stop(p);
+			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++;
+	hlist_del_init(&delayed.node);
+	spin_unlock(&current->sighand->siglock);
+	syscall_tracepoint_update(p);
+	write_unlock_irq(&tasklist_lock);
+
+	if (pidfile)
+		fd_install(pidfd, pidfile);
+
+	proc_fork_connector(p);
+	sched_post_fork(p);
+	cgroup_post_fork(p, args);
+	perf_event_fork(p);
+
+	trace_task_newtask(p, clone_flags);
+	uprobe_copy_process(p, clone_flags);
+	user_events_fork(p, clone_flags);
+
+	copy_oom_score_adj(clone_flags, p);
+
+	return p;
+
+bad_fork_cancel_cgroup:
+	sched_core_free(p);
+	spin_unlock(&current->sighand->siglock);
+	write_unlock_irq(&tasklist_lock);
+	cgroup_cancel_fork(p, args);
+bad_fork_put_pidfd:
+	if (clone_flags & CLONE_PIDFD) {
+		fput(pidfile);
+		put_unused_fd(pidfd);
+	}
+bad_fork_free_pid:
+	if (pid != &init_struct_pid)
+		free_pid(pid);
+bad_fork_cleanup_thread:
+	exit_thread(p);
+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) {
+		mm_clear_owner(p->mm, p);
+		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_security:
+	security_task_free(p);
+bad_fork_cleanup_audit:
+	audit_free(p);
+bad_fork_cleanup_perf:
+	perf_event_free_task(p);
+bad_fork_cleanup_policy:
+	lockdep_free_task(p);
+#ifdef CONFIG_NUMA
+	mpol_put(p->mempolicy);
+#endif
+bad_fork_cleanup_delayacct:
+	delayacct_tsk_free(p);
+bad_fork_cleanup_count:
+	dec_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
+	exit_creds(p);
+bad_fork_free:
+	WRITE_ONCE(p->__state, TASK_DEAD);
+	exit_task_stack_account(p);
+	put_task_stack(p);
+	delayed_free_task(p);
+fork_out:
+	spin_lock_irq(&current->sighand->siglock);
+	hlist_del_init(&delayed.node);
+	spin_unlock_irq(&current->sighand->siglock);
+	return ERR_PTR(retval);
+}
+
+static inline void init_idle_pids(struct task_struct *idle)
+{
+	enum pid_type type;
+
+	for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
+		INIT_HLIST_NODE(&idle->pid_links[type]); /* not really needed */
+		init_task_pid(idle, type, &init_struct_pid);
+	}
+}
+
+static int idle_dummy(void *dummy)
+{
+	/* This function is never called */
+	return 0;
+}
+
+struct task_struct * __init fork_idle(int cpu)
+{
+	struct task_struct *task;
+	struct kernel_clone_args args = {
+		.flags		= CLONE_VM,
+		.fn		= &idle_dummy,
+		.fn_arg		= NULL,
+		.kthread	= 1,
+		.idle		= 1,
+	};
+
+	task = copy_process(&init_struct_pid, 0, cpu_to_node(cpu), &args);
+	if (!IS_ERR(task)) {
+		init_idle_pids(task);
+		init_idle(task, cpu);
+	}
+
+	return task;
+}
+
+/*
+ * This is like kernel_clone(), but shaved down and tailored to just
+ * creating io_uring workers. It returns a created task, or an error pointer.
+ * The returned task is inactive, and the caller must fire it up through
+ * wake_up_new_task(p). All signals are blocked in the created task.
+ */
+struct task_struct *create_io_thread(int (*fn)(void *), void *arg, int node)
+{
+	unsigned long flags = CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|
+				CLONE_IO;
+	struct kernel_clone_args args = {
+		.flags		= ((lower_32_bits(flags) | CLONE_VM |
+				    CLONE_UNTRACED) & ~CSIGNAL),
+		.exit_signal	= (lower_32_bits(flags) & CSIGNAL),
+		.fn		= fn,
+		.fn_arg		= arg,
+		.io_thread	= 1,
+		.user_worker	= 1,
+	};
+
+	return copy_process(NULL, 0, node, &args);
+}
+
+/*
+ *  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.
+ *
+ * args->exit_signal is expected to be checked for sanity by the caller.
+ */
+pid_t kernel_clone(struct kernel_clone_args *args)
+{
+	u64 clone_flags = args->flags;
+	struct completion vfork;
+	struct pid *pid;
+	struct task_struct *p;
+	int trace = 0;
+	pid_t nr;
+
+	/*
+	 * For legacy clone() calls, CLONE_PIDFD uses the parent_tid argument
+	 * to return the pidfd. Hence, CLONE_PIDFD and CLONE_PARENT_SETTID are
+	 * mutually exclusive. With clone3() CLONE_PIDFD has grown a separate
+	 * field in struct clone_args and it still doesn't make sense to have
+	 * them both point at the same memory location. Performing this check
+	 * here has the advantage that we don't need to have a separate helper
+	 * to check for legacy clone().
+	 */
+	if ((args->flags & CLONE_PIDFD) &&
+	    (args->flags & CLONE_PARENT_SETTID) &&
+	    (args->pidfd == args->parent_tid))
+		return -EINVAL;
+
+	/*
+	 * 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 (args->exit_signal != SIGCHLD)
+			trace = PTRACE_EVENT_CLONE;
+		else
+			trace = PTRACE_EVENT_FORK;
+
+		if (likely(!ptrace_event_enabled(current, trace)))
+			trace = 0;
+	}
+
+	p = copy_process(NULL, trace, NUMA_NO_NODE, args);
+	add_latent_entropy();
+
+	if (IS_ERR(p))
+		return PTR_ERR(p);
+
+	/*
+	 * Do this prior waking up the new thread - the thread pointer
+	 * might get invalid after that point, if the thread exits quickly.
+	 */
+	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, args->parent_tid);
+
+	if (clone_flags & CLONE_VFORK) {
+		p->vfork_done = &vfork;
+		init_completion(&vfork);
+		get_task_struct(p);
+	}
+
+	if (IS_ENABLED(CONFIG_LRU_GEN) && !(clone_flags & CLONE_VM)) {
+		/* lock the task to synchronize with memcg migration */
+		task_lock(p);
+		lru_gen_add_mm(p->mm);
+		task_unlock(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);
+	return nr;
+}
+
+/*
+ * Create a kernel thread.
+ */
+pid_t kernel_thread(int (*fn)(void *), void *arg, const char *name,
+		    unsigned long flags)
+{
+	struct kernel_clone_args args = {
+		.flags		= ((lower_32_bits(flags) | CLONE_VM |
+				    CLONE_UNTRACED) & ~CSIGNAL),
+		.exit_signal	= (lower_32_bits(flags) & CSIGNAL),
+		.fn		= fn,
+		.fn_arg		= arg,
+		.name		= name,
+		.kthread	= 1,
+	};
+
+	return kernel_clone(&args);
+}
+
+/*
+ * Create a user mode thread.
+ */
+pid_t user_mode_thread(int (*fn)(void *), void *arg, unsigned long flags)
+{
+	struct kernel_clone_args args = {
+		.flags		= ((lower_32_bits(flags) | CLONE_VM |
+				    CLONE_UNTRACED) & ~CSIGNAL),
+		.exit_signal	= (lower_32_bits(flags) & CSIGNAL),
+		.fn		= fn,
+		.fn_arg		= arg,
+	};
+
+	return kernel_clone(&args);
+}
+
+#ifdef __ARCH_WANT_SYS_FORK
+SYSCALL_DEFINE0(fork)
+{
+#ifdef CONFIG_MMU
+	struct kernel_clone_args args = {
+		.exit_signal = SIGCHLD,
+	};
+
+	return kernel_clone(&args);
+#else
+	/* can not support in nommu mode */
+	return -EINVAL;
+#endif
+}
+#endif
+
+#ifdef __ARCH_WANT_SYS_VFORK
+SYSCALL_DEFINE0(vfork)
+{
+	struct kernel_clone_args args = {
+		.flags		= CLONE_VFORK | CLONE_VM,
+		.exit_signal	= SIGCHLD,
+	};
+
+	return kernel_clone(&args);
+}
+#endif
+
+#ifdef __ARCH_WANT_SYS_CLONE
+#ifdef CONFIG_CLONE_BACKWARDS
+SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
+		 int __user *, parent_tidptr,
+		 unsigned long, tls,
+		 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,
+		 unsigned long, tls)
+#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,
+		unsigned long, tls)
+#else
+SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
+		 int __user *, parent_tidptr,
+		 int __user *, child_tidptr,
+		 unsigned long, tls)
+#endif
+{
+	struct kernel_clone_args args = {
+		.flags		= (lower_32_bits(clone_flags) & ~CSIGNAL),
+		.pidfd		= parent_tidptr,
+		.child_tid	= child_tidptr,
+		.parent_tid	= parent_tidptr,
+		.exit_signal	= (lower_32_bits(clone_flags) & CSIGNAL),
+		.stack		= newsp,
+		.tls		= tls,
+	};
+
+	return kernel_clone(&args);
+}
+#endif
+
+#ifdef __ARCH_WANT_SYS_CLONE3
+
+noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
+					      struct clone_args __user *uargs,
+					      size_t usize)
+{
+	int err;
+	struct clone_args args;
+	pid_t *kset_tid = kargs->set_tid;
+
+	BUILD_BUG_ON(offsetofend(struct clone_args, tls) !=
+		     CLONE_ARGS_SIZE_VER0);
+	BUILD_BUG_ON(offsetofend(struct clone_args, set_tid_size) !=
+		     CLONE_ARGS_SIZE_VER1);
+	BUILD_BUG_ON(offsetofend(struct clone_args, cgroup) !=
+		     CLONE_ARGS_SIZE_VER2);
+	BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER2);
+
+	if (unlikely(usize > PAGE_SIZE))
+		return -E2BIG;
+	if (unlikely(usize < CLONE_ARGS_SIZE_VER0))
+		return -EINVAL;
+
+	err = copy_struct_from_user(&args, sizeof(args), uargs, usize);
+	if (err)
+		return err;
+
+	if (unlikely(args.set_tid_size > MAX_PID_NS_LEVEL))
+		return -EINVAL;
+
+	if (unlikely(!args.set_tid && args.set_tid_size > 0))
+		return -EINVAL;
+
+	if (unlikely(args.set_tid && args.set_tid_size == 0))
+		return -EINVAL;
+
+	/*
+	 * Verify that higher 32bits of exit_signal are unset and that
+	 * it is a valid signal
+	 */
+	if (unlikely((args.exit_signal & ~((u64)CSIGNAL)) ||
+		     !valid_signal(args.exit_signal)))
+		return -EINVAL;
+
+	if ((args.flags & CLONE_INTO_CGROUP) &&
+	    (args.cgroup > INT_MAX || usize < CLONE_ARGS_SIZE_VER2))
+		return -EINVAL;
+
+	*kargs = (struct kernel_clone_args){
+		.flags		= args.flags,
+		.pidfd		= u64_to_user_ptr(args.pidfd),
+		.child_tid	= u64_to_user_ptr(args.child_tid),
+		.parent_tid	= u64_to_user_ptr(args.parent_tid),
+		.exit_signal	= args.exit_signal,
+		.stack		= args.stack,
+		.stack_size	= args.stack_size,
+		.tls		= args.tls,
+		.set_tid_size	= args.set_tid_size,
+		.cgroup		= args.cgroup,
+	};
+
+	if (args.set_tid &&
+		copy_from_user(kset_tid, u64_to_user_ptr(args.set_tid),
+			(kargs->set_tid_size * sizeof(pid_t))))
+		return -EFAULT;
+
+	kargs->set_tid = kset_tid;
+
+	return 0;
+}
+
+/**
+ * clone3_stack_valid - check and prepare stack
+ * @kargs: kernel clone args
+ *
+ * Verify that the stack arguments userspace gave us are sane.
+ * In addition, set the stack direction for userspace since it's easy for us to
+ * determine.
+ */
+static inline bool clone3_stack_valid(struct kernel_clone_args *kargs)
+{
+	if (kargs->stack == 0) {
+		if (kargs->stack_size > 0)
+			return false;
+	} else {
+		if (kargs->stack_size == 0)
+			return false;
+
+		if (!access_ok((void __user *)kargs->stack, kargs->stack_size))
+			return false;
+
+#if !defined(CONFIG_STACK_GROWSUP) && !defined(CONFIG_IA64)
+		kargs->stack += kargs->stack_size;
+#endif
+	}
+
+	return true;
+}
+
+static bool clone3_args_valid(struct kernel_clone_args *kargs)
+{
+	/* Verify that no unknown flags are passed along. */
+	if (kargs->flags &
+	    ~(CLONE_LEGACY_FLAGS | CLONE_CLEAR_SIGHAND | CLONE_INTO_CGROUP))
+		return false;
+
+	/*
+	 * - make the CLONE_DETACHED bit reusable for clone3
+	 * - make the CSIGNAL bits reusable for clone3
+	 */
+	if (kargs->flags & (CLONE_DETACHED | (CSIGNAL & (~CLONE_NEWTIME))))
+		return false;
+
+	if ((kargs->flags & (CLONE_SIGHAND | CLONE_CLEAR_SIGHAND)) ==
+	    (CLONE_SIGHAND | CLONE_CLEAR_SIGHAND))
+		return false;
+
+	if ((kargs->flags & (CLONE_THREAD | CLONE_PARENT)) &&
+	    kargs->exit_signal)
+		return false;
+
+	if (!clone3_stack_valid(kargs))
+		return false;
+
+	return true;
+}
+
+/**
+ * clone3 - create a new process with specific properties
+ * @uargs: argument structure
+ * @size:  size of @uargs
+ *
+ * clone3() is the extensible successor to clone()/clone2().
+ * It takes a struct as argument that is versioned by its size.
+ *
+ * Return: On success, a positive PID for the child process.
+ *         On error, a negative errno number.
+ */
+SYSCALL_DEFINE2(clone3, struct clone_args __user *, uargs, size_t, size)
+{
+	int err;
+
+	struct kernel_clone_args kargs;
+	pid_t set_tid[MAX_PID_NS_LEVEL];
+
+	kargs.set_tid = set_tid;
+
+	err = copy_clone_args_from_user(&kargs, uargs, size);
+	if (err)
+		return err;
+
+	if (!clone3_args_valid(&kargs))
+		return -EINVAL;
+
+	return kernel_clone(&kargs);
+}
+#endif
+
+void walk_process_tree(struct task_struct *top, proc_visitor visitor, void *data)
+{
+	struct task_struct *leader, *parent, *child;
+	int res;
+
+	read_lock(&tasklist_lock);
+	leader = top = top->group_leader;
+down:
+	for_each_thread(leader, parent) {
+		list_for_each_entry(child, &parent->children, sibling) {
+			res = visitor(child, data);
+			if (res) {
+				if (res < 0)
+					goto out;
+				leader = child;
+				goto down;
+			}
+up:
+			;
+		}
+	}
+
+	if (leader != top) {
+		child = leader;
+		parent = child->real_parent;
+		leader = parent->group_leader;
+		goto up;
+	}
+out:
+	read_unlock(&tasklist_lock);
+}
+
+#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 mm_cache_init(void)
+{
+	unsigned int mm_size;
+
+	/*
+	 * The mm_cpumask is located at the end of mm_struct, and is
+	 * dynamically sized based on the maximum CPU number this system
+	 * can have, taking hotplug into account (nr_cpu_ids).
+	 */
+	mm_size = sizeof(struct mm_struct) + cpumask_size() + mm_cid_size();
+
+	mm_cachep = kmem_cache_create_usercopy("mm_struct",
+			mm_size, ARCH_MIN_MMSTRUCT_ALIGN,
+			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
+			offsetof(struct mm_struct, saved_auxv),
+			sizeof_field(struct mm_struct, saved_auxv),
+			NULL);
+}
+
+void __init proc_caches_init(void)
+{
+	sighand_cachep = kmem_cache_create("sighand_cache",
+			sizeof(struct sighand_struct), 0,
+			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
+			SLAB_ACCOUNT, sighand_ctor);
+	signal_cachep = kmem_cache_create("signal_cache",
+			sizeof(struct signal_struct), 0,
+			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
+			NULL);
+	files_cachep = kmem_cache_create("files_cache",
+			sizeof(struct files_struct), 0,
+			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
+			NULL);
+	fs_cachep = kmem_cache_create("fs_cache",
+			sizeof(struct fs_struct), 0,
+			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
+			NULL);
+
+	vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_ACCOUNT);
+#ifdef CONFIG_PER_VMA_LOCK
+	vma_lock_cachep = KMEM_CACHE(vma_lock, SLAB_PANIC|SLAB_ACCOUNT);
+#endif
+	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|CLONE_NEWCGROUP|
+				CLONE_NEWTIME))
+		return -EINVAL;
+	/*
+	 * Not implemented, but pretend it works if there is nothing
+	 * to unshare.  Note that unsharing the address space or the
+	 * signal handlers also need to unshare the signal queues (aka
+	 * CLONE_THREAD).
+	 */
+	if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
+		if (!thread_group_empty(current))
+			return -EINVAL;
+	}
+	if (unshare_flags & (CLONE_SIGHAND | CLONE_VM)) {
+		if (refcount_read(&current->sighand->count) > 1)
+			return -EINVAL;
+	}
+	if (unshare_flags & CLONE_VM) {
+		if (!current_is_single_threaded())
+			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
+ */
+int unshare_fd(unsigned long unshare_flags, unsigned int max_fds,
+	       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, max_fds, &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 kernel_clone() 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.
+ */
+int ksys_unshare(unsigned long unshare_flags)
+{
+	struct fs_struct *fs, *new_fs = NULL;
+	struct files_struct *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 group
+	 * and unshare the filesystem root and working directories.
+	 */
+	if (unshare_flags & CLONE_NEWUSER)
+		unshare_flags |= CLONE_THREAD | CLONE_FS;
+	/*
+	 * If unsharing vm, must also unshare signal handlers.
+	 */
+	if (unshare_flags & CLONE_VM)
+		unshare_flags |= CLONE_SIGHAND;
+	/*
+	 * If unsharing a signal handlers, must also unshare the signal queues.
+	 */
+	if (unshare_flags & CLONE_SIGHAND)
+		unshare_flags |= CLONE_THREAD;
+	/*
+	 * 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, NR_OPEN_MAX, &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_cred) {
+		err = set_cred_ucounts(new_cred);
+		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)
+			swap(current->files, new_fd);
+
+		task_unlock(current);
+
+		if (new_cred) {
+			/* Install the new user namespace */
+			commit_creds(new_cred);
+			new_cred = NULL;
+		}
+	}
+
+	perf_event_namespaces(current);
+
+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;
+}
+
+SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
+{
+	return ksys_unshare(unshare_flags);
+}
+
+/*
+ *	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(void)
+{
+	struct task_struct *task = current;
+	struct files_struct *old, *copy = NULL;
+	int error;
+
+	error = unshare_fd(CLONE_FILES, NR_OPEN_MAX, &copy);
+	if (error || !copy)
+		return error;
+
+	old = task->files;
+	task_lock(task);
+	task->files = copy;
+	task_unlock(task);
+	put_files_struct(old);
+	return 0;
+}
+
+int sysctl_max_threads(struct ctl_table *table, int write,
+		       void *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct ctl_table t;
+	int ret;
+	int threads = max_threads;
+	int min = 1;
+	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;
+
+	max_threads = threads;
+
+	return 0;
+}