1 files changed, 374 insertions, 91 deletions

diff --git a/kernel/kthread.c b/kernel/kthread.c
index b262f47046ca..f97fd01a2932 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -1,13 +1,17 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /* Kernel thread helper functions.
  *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
+ *   Copyright (C) 2009 Red Hat, Inc.
  *
  * Creation is done via kthreadd, so that we get a clean environment
  * even if we're invoked from userspace (think modprobe, hotplug cpu,
  * etc.).
  */
 #include <uapi/linux/sched/types.h>
+#include <linux/mm.h>
+#include <linux/mmu_context.h>
 #include <linux/sched.h>
+#include <linux/sched/mm.h>
 #include <linux/sched/task.h>
 #include <linux/kthread.h>
 #include <linux/completion.h>
@@ -23,8 +27,10 @@
 #include <linux/ptrace.h>
 #include <linux/uaccess.h>
 #include <linux/numa.h>
+#include <linux/sched/isolation.h>
 #include <trace/events/sched.h>
 
+
 static DEFINE_SPINLOCK(kthread_create_lock);
 static LIST_HEAD(kthread_create_list);
 struct task_struct *kthreadd_task;
@@ -46,12 +52,16 @@ struct kthread_create_info
 struct kthread {
 	unsigned long flags;
 	unsigned int cpu;
+	int result;
+	int (*threadfn)(void *);
 	void *data;
 	struct completion parked;
 	struct completion exited;
 #ifdef CONFIG_BLK_CGROUP
 	struct cgroup_subsys_state *blkcg_css;
 #endif
+	/* To store the full name if task comm is truncated. */
+	char *full_name;
 };
 
 enum KTHREAD_BITS {
@@ -60,20 +70,60 @@ enum KTHREAD_BITS {
 	KTHREAD_SHOULD_PARK,
 };
 
-static inline void set_kthread_struct(void *kthread)
+static inline struct kthread *to_kthread(struct task_struct *k)
 {
-	/*
-	 * We abuse ->set_child_tid to avoid the new member and because it
-	 * can't be wrongly copied by copy_process(). We also rely on fact
-	 * that the caller can't exec, so PF_KTHREAD can't be cleared.
-	 */
-	current->set_child_tid = (__force void __user *)kthread;
+	WARN_ON(!(k->flags & PF_KTHREAD));
+	return k->worker_private;
 }
 
-static inline struct kthread *to_kthread(struct task_struct *k)
+/*
+ * Variant of to_kthread() that doesn't assume @p is a kthread.
+ *
+ * Per construction; when:
+ *
+ *   (p->flags & PF_KTHREAD) && p->worker_private
+ *
+ * the task is both a kthread and struct kthread is persistent. However
+ * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and
+ * begin_new_exec()).
+ */
+static inline struct kthread *__to_kthread(struct task_struct *p)
 {
-	WARN_ON(!(k->flags & PF_KTHREAD));
-	return (__force void *)k->set_child_tid;
+	void *kthread = p->worker_private;
+	if (kthread && !(p->flags & PF_KTHREAD))
+		kthread = NULL;
+	return kthread;
+}
+
+void get_kthread_comm(char *buf, size_t buf_size, struct task_struct *tsk)
+{
+	struct kthread *kthread = to_kthread(tsk);
+
+	if (!kthread || !kthread->full_name) {
+		__get_task_comm(buf, buf_size, tsk);
+		return;
+	}
+
+	strscpy_pad(buf, kthread->full_name, buf_size);
+}
+
+bool set_kthread_struct(struct task_struct *p)
+{
+	struct kthread *kthread;
+
+	if (WARN_ON_ONCE(to_kthread(p)))
+		return false;
+
+	kthread = kzalloc(sizeof(*kthread), GFP_KERNEL);
+	if (!kthread)
+		return false;
+
+	init_completion(&kthread->exited);
+	init_completion(&kthread->parked);
+	p->vfork_done = &kthread->exited;
+
+	p->worker_private = kthread;
+	return true;
 }
 
 void free_kthread_struct(struct task_struct *k)
@@ -81,13 +131,17 @@ void free_kthread_struct(struct task_struct *k)
 	struct kthread *kthread;
 
 	/*
-	 * Can be NULL if this kthread was created by kernel_thread()
-	 * or if kmalloc() in kthread() failed.
+	 * Can be NULL if kmalloc() in set_kthread_struct() failed.
 	 */
 	kthread = to_kthread(k);
+	if (!kthread)
+		return;
+
 #ifdef CONFIG_BLK_CGROUP
-	WARN_ON_ONCE(kthread && kthread->blkcg_css);
+	WARN_ON_ONCE(kthread->blkcg_css);
 #endif
+	k->worker_private = NULL;
+	kfree(kthread->full_name);
 	kfree(kthread);
 }
 
@@ -153,6 +207,21 @@ bool kthread_freezable_should_stop(bool *was_frozen)
 EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
 
 /**
+ * kthread_func - return the function specified on kthread creation
+ * @task: kthread task in question
+ *
+ * Returns NULL if the task is not a kthread.
+ */
+void *kthread_func(struct task_struct *task)
+{
+	struct kthread *kthread = __to_kthread(task);
+	if (kthread)
+		return kthread->threadfn;
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(kthread_func);
+
+/**
  * kthread_data - return data value specified on kthread creation
  * @task: kthread task in question
  *
@@ -164,6 +233,7 @@ void *kthread_data(struct task_struct *task)
 {
 	return to_kthread(task)->data;
 }
+EXPORT_SYMBOL_GPL(kthread_data);
 
 /**
  * kthread_probe_data - speculative version of kthread_data()
@@ -176,10 +246,11 @@ void *kthread_data(struct task_struct *task)
  */
 void *kthread_probe_data(struct task_struct *task)
 {
-	struct kthread *kthread = to_kthread(task);
+	struct kthread *kthread = __to_kthread(task);
 	void *data = NULL;
 
-	probe_kernel_read(&data, &kthread->data, sizeof(data));
+	if (kthread)
+		copy_from_kernel_nofault(&data, &kthread->data, sizeof(data));
 	return data;
 }
 
@@ -199,8 +270,15 @@ static void __kthread_parkme(struct kthread *self)
 		if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags))
 			break;
 
+		/*
+		 * Thread is going to call schedule(), do not preempt it,
+		 * or the caller of kthread_park() may spend more time in
+		 * wait_task_inactive().
+		 */
+		preempt_disable();
 		complete(&self->parked);
-		schedule();
+		schedule_preempt_disabled();
+		preempt_enable();
 	}
 	__set_current_state(TASK_RUNNING);
 }
@@ -211,8 +289,47 @@ void kthread_parkme(void)
 }
 EXPORT_SYMBOL_GPL(kthread_parkme);
 
+/**
+ * kthread_exit - Cause the current kthread return @result to kthread_stop().
+ * @result: The integer value to return to kthread_stop().
+ *
+ * While kthread_exit can be called directly, it exists so that
+ * functions which do some additional work in non-modular code such as
+ * module_put_and_kthread_exit can be implemented.
+ *
+ * Does not return.
+ */
+void __noreturn kthread_exit(long result)
+{
+	struct kthread *kthread = to_kthread(current);
+	kthread->result = result;
+	do_exit(0);
+}
+
+/**
+ * kthread_complete_and_exit - Exit the current kthread.
+ * @comp: Completion to complete
+ * @code: The integer value to return to kthread_stop().
+ *
+ * If present complete @comp and the reuturn code to kthread_stop().
+ *
+ * A kernel thread whose module may be removed after the completion of
+ * @comp can use this function exit safely.
+ *
+ * Does not return.
+ */
+void __noreturn kthread_complete_and_exit(struct completion *comp, long code)
+{
+	if (comp)
+		complete(comp);
+
+	kthread_exit(code);
+}
+EXPORT_SYMBOL(kthread_complete_and_exit);
+
 static int kthread(void *_create)
 {
+	static const struct sched_param param = { .sched_priority = 0 };
 	/* Copy data: it's on kthread's stack */
 	struct kthread_create_info *create = _create;
 	int (*threadfn)(void *data) = create->threadfn;
@@ -221,32 +338,36 @@ static int kthread(void *_create)
 	struct kthread *self;
 	int ret;
 
-	self = kzalloc(sizeof(*self), GFP_KERNEL);
-	set_kthread_struct(self);
+	self = to_kthread(current);
 
-	/* If user was SIGKILLed, I release the structure. */
+	/* Release the structure when caller killed by a fatal signal. */
 	done = xchg(&create->done, NULL);
 	if (!done) {
 		kfree(create);
-		do_exit(-EINTR);
-	}
-
-	if (!self) {
-		create->result = ERR_PTR(-ENOMEM);
-		complete(done);
-		do_exit(-ENOMEM);
+		kthread_exit(-EINTR);
 	}
 
+	self->threadfn = threadfn;
 	self->data = data;
-	init_completion(&self->exited);
-	init_completion(&self->parked);
-	current->vfork_done = &self->exited;
+
+	/*
+	 * The new thread inherited kthreadd's priority and CPU mask. Reset
+	 * back to default in case they have been changed.
+	 */
+	sched_setscheduler_nocheck(current, SCHED_NORMAL, &param);
+	set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_TYPE_KTHREAD));
 
 	/* OK, tell user we're spawned, wait for stop or wakeup */
 	__set_current_state(TASK_UNINTERRUPTIBLE);
 	create->result = current;
+	/*
+	 * Thread is going to call schedule(), do not preempt it,
+	 * or the creator may spend more time in wait_task_inactive().
+	 */
+	preempt_disable();
 	complete(done);
-	schedule();
+	schedule_preempt_disabled();
+	preempt_enable();
 
 	ret = -EINTR;
 	if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
@@ -254,10 +375,10 @@ static int kthread(void *_create)
 		__kthread_parkme(self);
 		ret = threadfn(data);
 	}
-	do_exit(ret);
+	kthread_exit(ret);
 }
 
-/* called from do_fork() to get node information for about to be created task */
+/* called from kernel_clone() to get node information for about to be created task */
 int tsk_fork_get_node(struct task_struct *tsk)
 {
 #ifdef CONFIG_NUMA
@@ -277,7 +398,7 @@ static void create_kthread(struct kthread_create_info *create)
 	/* We want our own signal handler (we take no signals by default). */
 	pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
 	if (pid < 0) {
-		/* If user was SIGKILLed, I release the structure. */
+		/* Release the structure when caller killed by a fatal signal. */
 		struct completion *done = xchg(&create->done, NULL);
 
 		if (!done) {
@@ -319,9 +440,9 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
 	 */
 	if (unlikely(wait_for_completion_killable(&done))) {
 		/*
-		 * If I was SIGKILLed before kthreadd (or new kernel thread)
-		 * calls complete(), leave the cleanup of this structure to
-		 * that thread.
+		 * If I was killed by a fatal signal before kthreadd (or new
+		 * kernel thread) calls complete(), leave the cleanup of this
+		 * structure to that thread.
 		 */
 		if (xchg(&create->done, NULL))
 			return ERR_PTR(-EINTR);
@@ -333,21 +454,24 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
 	}
 	task = create->result;
 	if (!IS_ERR(task)) {
-		static const struct sched_param param = { .sched_priority = 0 };
 		char name[TASK_COMM_LEN];
+		va_list aq;
+		int len;
 
 		/*
 		 * task is already visible to other tasks, so updating
 		 * COMM must be protected.
 		 */
-		vsnprintf(name, sizeof(name), namefmt, args);
+		va_copy(aq, args);
+		len = vsnprintf(name, sizeof(name), namefmt, aq);
+		va_end(aq);
+		if (len >= TASK_COMM_LEN) {
+			struct kthread *kthread = to_kthread(task);
+
+			/* leave it truncated when out of memory. */
+			kthread->full_name = kvasprintf(GFP_KERNEL, namefmt, args);
+		}
 		set_task_comm(task, name);
-		/*
-		 * root may have changed our (kthreadd's) priority or CPU mask.
-		 * The kernel thread should not inherit these properties.
-		 */
-		sched_setscheduler_nocheck(task, SCHED_NORMAL, &param);
-		set_cpus_allowed_ptr(task, cpu_all_mask);
 	}
 	kfree(create);
 	return task;
@@ -368,7 +492,7 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
  * If thread is going to be bound on a particular cpu, give its node
  * in @node, to get NUMA affinity for kthread stack, or else give NUMA_NO_NODE.
  * When woken, the thread will run @threadfn() with @data as its
- * argument. @threadfn() can either call do_exit() directly if it is a
+ * argument. @threadfn() can either return directly if it is a
  * standalone thread for which no one will call kthread_stop(), or
  * return when 'kthread_should_stop()' is true (which means
  * kthread_stop() has been called).  The return value should be zero
@@ -392,7 +516,7 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 }
 EXPORT_SYMBOL(kthread_create_on_node);
 
-static void __kthread_bind_mask(struct task_struct *p, const struct cpumask *mask, long state)
+static void __kthread_bind_mask(struct task_struct *p, const struct cpumask *mask, unsigned int state)
 {
 	unsigned long flags;
 
@@ -408,7 +532,7 @@ static void __kthread_bind_mask(struct task_struct *p, const struct cpumask *mas
 	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 }
 
-static void __kthread_bind(struct task_struct *p, unsigned int cpu, long state)
+static void __kthread_bind(struct task_struct *p, unsigned int cpu, unsigned int state)
 {
 	__kthread_bind_mask(p, cpumask_of(cpu), state);
 }
@@ -442,7 +566,6 @@ EXPORT_SYMBOL(kthread_bind);
  *	     to "name.*%u". Code fills in cpu number.
  *
  * Description: This helper function creates and names a kernel thread
- * The thread will be woken and put into park mode.
  */
 struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
 					  void *data, unsigned int cpu,
@@ -456,10 +579,36 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
 		return p;
 	kthread_bind(p, cpu);
 	/* CPU hotplug need to bind once again when unparking the thread. */
-	set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
 	to_kthread(p)->cpu = cpu;
 	return p;
 }
+EXPORT_SYMBOL(kthread_create_on_cpu);
+
+void kthread_set_per_cpu(struct task_struct *k, int cpu)
+{
+	struct kthread *kthread = to_kthread(k);
+	if (!kthread)
+		return;
+
+	WARN_ON_ONCE(!(k->flags & PF_NO_SETAFFINITY));
+
+	if (cpu < 0) {
+		clear_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
+		return;
+	}
+
+	kthread->cpu = cpu;
+	set_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
+}
+
+bool kthread_is_per_cpu(struct task_struct *p)
+{
+	struct kthread *kthread = __to_kthread(p);
+	if (!kthread)
+		return false;
+
+	return test_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
+}
 
 /**
  * kthread_unpark - unpark a thread created by kthread_create().
@@ -538,7 +687,7 @@ EXPORT_SYMBOL_GPL(kthread_park);
  * instead of calling wake_up_process(): the thread will exit without
  * calling threadfn().
  *
- * If threadfn() may call do_exit() itself, the caller must ensure
+ * If threadfn() may call kthread_exit() itself, the caller must ensure
  * task_struct can't go away.
  *
  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
@@ -555,9 +704,10 @@ int kthread_stop(struct task_struct *k)
 	kthread = to_kthread(k);
 	set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
 	kthread_unpark(k);
+	set_tsk_thread_flag(k, TIF_NOTIFY_SIGNAL);
 	wake_up_process(k);
 	wait_for_completion(&kthread->exited);
-	ret = k->exit_code;
+	ret = kthread->result;
 	put_task_struct(k);
 
 	trace_sched_kthread_stop_ret(ret);
@@ -572,7 +722,7 @@ int kthreadd(void *unused)
 	/* Setup a clean context for our children to inherit. */
 	set_task_comm(tsk, "kthreadd");
 	ignore_signals(tsk);
-	set_cpus_allowed_ptr(tsk, cpu_all_mask);
+	set_cpus_allowed_ptr(tsk, housekeeping_cpumask(HK_TYPE_KTHREAD));
 	set_mems_allowed(node_states[N_MEMORY]);
 
 	current->flags |= PF_NOFREEZE;
@@ -667,8 +817,15 @@ repeat:
 	raw_spin_unlock_irq(&worker->lock);
 
 	if (work) {
+		kthread_work_func_t func = work->func;
 		__set_current_state(TASK_RUNNING);
+		trace_sched_kthread_work_execute_start(work);
 		work->func(work);
+		/*
+		 * Avoid dereferencing work after this point.  The trace
+		 * event only cares about the address.
+		 */
+		trace_sched_kthread_work_execute_end(work, func);
 	} else if (!freezing(current))
 		schedule();
 
@@ -720,7 +877,7 @@ fail_task:
  *
  * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
  * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
- * when the worker was SIGKILLed.
+ * when the caller was killed by a fatal signal.
  */
 struct kthread_worker *
 kthread_create_worker(unsigned int flags, const char namefmt[], ...)
@@ -738,7 +895,7 @@ EXPORT_SYMBOL(kthread_create_worker);
 
 /**
  * kthread_create_worker_on_cpu - create a kthread worker and bind it
- *	it to a given CPU and the associated NUMA node.
+ *	to a given CPU and the associated NUMA node.
  * @cpu: CPU number
  * @flags: flags modifying the default behavior of the worker
  * @namefmt: printf-style name for the kthread worker (task).
@@ -749,9 +906,27 @@ EXPORT_SYMBOL(kthread_create_worker);
  * A good practice is to add the cpu number also into the worker name.
  * For example, use kthread_create_worker_on_cpu(cpu, "helper/%d", cpu).
  *
- * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
+ * CPU hotplug:
+ * The kthread worker API is simple and generic. It just provides a way
+ * to create, use, and destroy workers.
+ *
+ * It is up to the API user how to handle CPU hotplug. They have to decide
+ * how to handle pending work items, prevent queuing new ones, and
+ * restore the functionality when the CPU goes off and on. There are a
+ * few catches:
+ *
+ *    - CPU affinity gets lost when it is scheduled on an offline CPU.
+ *
+ *    - The worker might not exist when the CPU was off when the user
+ *      created the workers.
+ *
+ * Good practice is to implement two CPU hotplug callbacks and to
+ * destroy/create the worker when the CPU goes down/up.
+ *
+ * Return:
+ * The pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
  * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
- * when the worker was SIGKILLed.
+ * when the caller was killed by a fatal signal.
  */
 struct kthread_worker *
 kthread_create_worker_on_cpu(int cpu, unsigned int flags,
@@ -797,6 +972,8 @@ static void kthread_insert_work(struct kthread_worker *worker,
 {
 	kthread_insert_work_sanity_check(worker, work);
 
+	trace_sched_kthread_work_queue_work(worker, work);
+
 	list_add_tail(&work->node, pos);
 	work->worker = worker;
 	if (!worker->current_work && likely(worker->task))
@@ -860,7 +1037,8 @@ void kthread_delayed_work_timer_fn(struct timer_list *t)
 	/* Move the work from worker->delayed_work_list. */
 	WARN_ON_ONCE(list_empty(&work->node));
 	list_del_init(&work->node);
-	kthread_insert_work(worker, work, &worker->work_list);
+	if (!work->canceling)
+		kthread_insert_work(worker, work, &worker->work_list);
 
 	raw_spin_unlock_irqrestore(&worker->lock, flags);
 }
@@ -981,8 +1159,38 @@ void kthread_flush_work(struct kthread_work *work)
 EXPORT_SYMBOL_GPL(kthread_flush_work);
 
 /*
- * This function removes the work from the worker queue. Also it makes sure
- * that it won't get queued later via the delayed work's timer.
+ * Make sure that the timer is neither set nor running and could
+ * not manipulate the work list_head any longer.
+ *
+ * The function is called under worker->lock. The lock is temporary
+ * released but the timer can't be set again in the meantime.
+ */
+static void kthread_cancel_delayed_work_timer(struct kthread_work *work,
+					      unsigned long *flags)
+{
+	struct kthread_delayed_work *dwork =
+		container_of(work, struct kthread_delayed_work, work);
+	struct kthread_worker *worker = work->worker;
+
+	/*
+	 * del_timer_sync() must be called to make sure that the timer
+	 * callback is not running. The lock must be temporary released
+	 * to avoid a deadlock with the callback. In the meantime,
+	 * any queuing is blocked by setting the canceling counter.
+	 */
+	work->canceling++;
+	raw_spin_unlock_irqrestore(&worker->lock, *flags);
+	del_timer_sync(&dwork->timer);
+	raw_spin_lock_irqsave(&worker->lock, *flags);
+	work->canceling--;
+}
+
+/*
+ * This function removes the work from the worker queue.
+ *
+ * It is called under worker->lock. The caller must make sure that
+ * the timer used by delayed work is not running, e.g. by calling
+ * kthread_cancel_delayed_work_timer().
  *
  * The work might still be in use when this function finishes. See the
  * current_work proceed by the worker.
@@ -990,28 +1198,8 @@ EXPORT_SYMBOL_GPL(kthread_flush_work);
  * Return: %true if @work was pending and successfully canceled,
  *	%false if @work was not pending
  */
-static bool __kthread_cancel_work(struct kthread_work *work, bool is_dwork,
-				  unsigned long *flags)
+static bool __kthread_cancel_work(struct kthread_work *work)
 {
-	/* Try to cancel the timer if exists. */
-	if (is_dwork) {
-		struct kthread_delayed_work *dwork =
-			container_of(work, struct kthread_delayed_work, work);
-		struct kthread_worker *worker = work->worker;
-
-		/*
-		 * del_timer_sync() must be called to make sure that the timer
-		 * callback is not running. The lock must be temporary released
-		 * to avoid a deadlock with the callback. In the meantime,
-		 * any queuing is blocked by setting the canceling counter.
-		 */
-		work->canceling++;
-		raw_spin_unlock_irqrestore(&worker->lock, *flags);
-		del_timer_sync(&dwork->timer);
-		raw_spin_lock_irqsave(&worker->lock, *flags);
-		work->canceling--;
-	}
-
 	/*
 	 * Try to remove the work from a worker list. It might either
 	 * be from worker->work_list or from worker->delayed_work_list.
@@ -1034,14 +1222,14 @@ static bool __kthread_cancel_work(struct kthread_work *work, bool is_dwork,
  * modify @dwork's timer so that it expires after @delay. If @delay is zero,
  * @work is guaranteed to be queued immediately.
  *
- * Return: %true if @dwork was pending and its timer was modified,
- * %false otherwise.
+ * Return: %false if @dwork was idle and queued, %true otherwise.
  *
  * A special case is when the work is being canceled in parallel.
  * It might be caused either by the real kthread_cancel_delayed_work_sync()
  * or yet another kthread_mod_delayed_work() call. We let the other command
- * win and return %false here. The caller is supposed to synchronize these
- * operations a reasonable way.
+ * win and return %true here. The return value can be used for reference
+ * counting and the number of queued works stays the same. Anyway, the caller
+ * is supposed to synchronize these operations a reasonable way.
  *
  * This function is safe to call from any context including IRQ handler.
  * See __kthread_cancel_work() and kthread_delayed_work_timer_fn()
@@ -1053,22 +1241,39 @@ bool kthread_mod_delayed_work(struct kthread_worker *worker,
 {
 	struct kthread_work *work = &dwork->work;
 	unsigned long flags;
-	int ret = false;
+	int ret;
 
 	raw_spin_lock_irqsave(&worker->lock, flags);
 
 	/* Do not bother with canceling when never queued. */
-	if (!work->worker)
+	if (!work->worker) {
+		ret = false;
 		goto fast_queue;
+	}
 
 	/* Work must not be used with >1 worker, see kthread_queue_work() */
 	WARN_ON_ONCE(work->worker != worker);
 
-	/* Do not fight with another command that is canceling this work. */
-	if (work->canceling)
+	/*
+	 * Temporary cancel the work but do not fight with another command
+	 * that is canceling the work as well.
+	 *
+	 * It is a bit tricky because of possible races with another
+	 * mod_delayed_work() and cancel_delayed_work() callers.
+	 *
+	 * The timer must be canceled first because worker->lock is released
+	 * when doing so. But the work can be removed from the queue (list)
+	 * only when it can be queued again so that the return value can
+	 * be used for reference counting.
+	 */
+	kthread_cancel_delayed_work_timer(work, &flags);
+	if (work->canceling) {
+		/* The number of works in the queue does not change. */
+		ret = true;
 		goto out;
+	}
+	ret = __kthread_cancel_work(work);
 
-	ret = __kthread_cancel_work(work, true, &flags);
 fast_queue:
 	__kthread_queue_delayed_work(worker, dwork, delay);
 out:
@@ -1090,7 +1295,10 @@ static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
 	/* Work must not be used with >1 worker, see kthread_queue_work(). */
 	WARN_ON_ONCE(work->worker != worker);
 
-	ret = __kthread_cancel_work(work, is_dwork, &flags);
+	if (is_dwork)
+		kthread_cancel_delayed_work_timer(work, &flags);
+
+	ret = __kthread_cancel_work(work);
 
 	if (worker->current_work != work)
 		goto out_fast;
@@ -1190,6 +1398,82 @@ void kthread_destroy_worker(struct kthread_worker *worker)
 }
 EXPORT_SYMBOL(kthread_destroy_worker);
 
+/**
+ * kthread_use_mm - make the calling kthread operate on an address space
+ * @mm: address space to operate on
+ */
+void kthread_use_mm(struct mm_struct *mm)
+{
+	struct mm_struct *active_mm;
+	struct task_struct *tsk = current;
+
+	WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
+	WARN_ON_ONCE(tsk->mm);
+
+	task_lock(tsk);
+	/* Hold off tlb flush IPIs while switching mm's */
+	local_irq_disable();
+	active_mm = tsk->active_mm;
+	if (active_mm != mm) {
+		mmgrab(mm);
+		tsk->active_mm = mm;
+	}
+	tsk->mm = mm;
+	membarrier_update_current_mm(mm);
+	switch_mm_irqs_off(active_mm, mm, tsk);
+	local_irq_enable();
+	task_unlock(tsk);
+#ifdef finish_arch_post_lock_switch
+	finish_arch_post_lock_switch();
+#endif
+
+	/*
+	 * When a kthread starts operating on an address space, the loop
+	 * in membarrier_{private,global}_expedited() may not observe
+	 * that tsk->mm, and not issue an IPI. Membarrier requires a
+	 * memory barrier after storing to tsk->mm, before accessing
+	 * user-space memory. A full memory barrier for membarrier
+	 * {PRIVATE,GLOBAL}_EXPEDITED is implicitly provided by
+	 * mmdrop(), or explicitly with smp_mb().
+	 */
+	if (active_mm != mm)
+		mmdrop(active_mm);
+	else
+		smp_mb();
+}
+EXPORT_SYMBOL_GPL(kthread_use_mm);
+
+/**
+ * kthread_unuse_mm - reverse the effect of kthread_use_mm()
+ * @mm: address space to operate on
+ */
+void kthread_unuse_mm(struct mm_struct *mm)
+{
+	struct task_struct *tsk = current;
+
+	WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
+	WARN_ON_ONCE(!tsk->mm);
+
+	task_lock(tsk);
+	/*
+	 * When a kthread stops operating on an address space, the loop
+	 * in membarrier_{private,global}_expedited() may not observe
+	 * that tsk->mm, and not issue an IPI. Membarrier requires a
+	 * memory barrier after accessing user-space memory, before
+	 * clearing tsk->mm.
+	 */
+	smp_mb__after_spinlock();
+	sync_mm_rss(mm);
+	local_irq_disable();
+	tsk->mm = NULL;
+	membarrier_update_current_mm(NULL);
+	/* active_mm is still 'mm' */
+	enter_lazy_tlb(mm, tsk);
+	local_irq_enable();
+	task_unlock(tsk);
+}
+EXPORT_SYMBOL_GPL(kthread_unuse_mm);
+
 #ifdef CONFIG_BLK_CGROUP
 /**
  * kthread_associate_blkcg - associate blkcg to current kthread
@@ -1238,5 +1522,4 @@ struct cgroup_subsys_state *kthread_blkcg(void)
 	}
 	return NULL;
 }
-EXPORT_SYMBOL(kthread_blkcg);
 #endif