task_work.c

  1// SPDX-License-Identifier: GPL-2.0
  2#include <linux/irq_work.h>
  3#include <linux/spinlock.h>
  4#include <linux/task_work.h>
  5#include <linux/resume_user_mode.h>
  6
  7static struct callback_head work_exited; /* all we need is ->next == NULL */
  8
  9#ifdef CONFIG_IRQ_WORK
 10static void task_work_set_notify_irq(struct irq_work *entry)
 11{
 12	/*
 13	 * no-op IPI
 14	 *
 15	 * TWA_NMI_CURRENT will already have set the TIF flag, all
 16	 * this interrupt does it tickle the return-to-user path.
 17	 */
 18}
 19static DEFINE_PER_CPU(struct irq_work, irq_work_NMI_resume) =
 20	IRQ_WORK_INIT_HARD(task_work_set_notify_irq);
 21#endif
 22
 23/**
 24 * task_work_add - ask the @task to execute @work->func()
 25 * @task: the task which should run the callback
 26 * @work: the callback to run
 27 * @notify: how to notify the targeted task
 28 *
 29 * Queue @work for task_work_run() below and notify the @task if @notify
 30 * is @TWA_RESUME, @TWA_SIGNAL, @TWA_SIGNAL_NO_IPI or @TWA_NMI_CURRENT.
 31 *
 32 * @TWA_SIGNAL works like signals, in that the it will interrupt the targeted
 33 * task and run the task_work, regardless of whether the task is currently
 34 * running in the kernel or userspace.
 35 * @TWA_SIGNAL_NO_IPI works like @TWA_SIGNAL, except it doesn't send a
 36 * reschedule IPI to force the targeted task to reschedule and run task_work.
 37 * This can be advantageous if there's no strict requirement that the
 38 * task_work be run as soon as possible, just whenever the task enters the
 39 * kernel anyway.
 40 * @TWA_RESUME work is run only when the task exits the kernel and returns to
 41 * user mode, or before entering guest mode.
 42 * @TWA_NMI_CURRENT works like @TWA_RESUME, except it can only be used for the
 43 * current @task and if the current context is NMI.
 44 *
 45 * Fails if the @task is exiting/exited and thus it can't process this @work.
 46 * Otherwise @work->func() will be called when the @task goes through one of
 47 * the aforementioned transitions, or exits.
 48 *
 49 * If the targeted task is exiting, then an error is returned and the work item
 50 * is not queued. It's up to the caller to arrange for an alternative mechanism
 51 * in that case.
 52 *
 53 * Note: there is no ordering guarantee on works queued here. The task_work
 54 * list is LIFO.
 55 *
 56 * RETURNS:
 57 * 0 if succeeds or -ESRCH.
 58 */
 59int task_work_add(struct task_struct *task, struct callback_head *work,
 60		  enum task_work_notify_mode notify)
 61{
 62	struct callback_head *head;
 63
 64	if (notify == TWA_NMI_CURRENT) {
 65		if (WARN_ON_ONCE(task != current))
 66			return -EINVAL;
 67		if (!IS_ENABLED(CONFIG_IRQ_WORK))
 68			return -EINVAL;
 69	} else {
 70		kasan_record_aux_stack(work);
 71	}
 72
 73	head = READ_ONCE(task->task_works);
 74	do {
 75		if (unlikely(head == &work_exited))
 76			return -ESRCH;
 77		work->next = head;
 78	} while (!try_cmpxchg(&task->task_works, &head, work));
 79
 80	switch (notify) {
 81	case TWA_NONE:
 82		break;
 83	case TWA_RESUME:
 84		set_notify_resume(task);
 85		break;
 86	case TWA_SIGNAL:
 87		set_notify_signal(task);
 88		break;
 89	case TWA_SIGNAL_NO_IPI:
 90		__set_notify_signal(task);
 91		break;
 92#ifdef CONFIG_IRQ_WORK
 93	case TWA_NMI_CURRENT:
 94		set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
 95		irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume));
 96		break;
 97#endif
 98	default:
 99		WARN_ON_ONCE(1);
100		break;
101	}
102
103	return 0;
104}
105
106/**
107 * task_work_cancel_match - cancel a pending work added by task_work_add()
108 * @task: the task which should execute the work
109 * @match: match function to call
110 * @data: data to be passed in to match function
111 *
112 * RETURNS:
113 * The found work or NULL if not found.
114 */
115struct callback_head *
116task_work_cancel_match(struct task_struct *task,
117		       bool (*match)(struct callback_head *, void *data),
118		       void *data)
119{
120	struct callback_head **pprev = &task->task_works;
121	struct callback_head *work;
122	unsigned long flags;
123
124	if (likely(!task_work_pending(task)))
125		return NULL;
126	/*
127	 * If cmpxchg() fails we continue without updating pprev.
128	 * Either we raced with task_work_add() which added the
129	 * new entry before this work, we will find it again. Or
130	 * we raced with task_work_run(), *pprev == NULL/exited.
131	 */
132	raw_spin_lock_irqsave(&task->pi_lock, flags);
133	work = READ_ONCE(*pprev);
134	while (work) {
135		if (!match(work, data)) {
136			pprev = &work->next;
137			work = READ_ONCE(*pprev);
138		} else if (try_cmpxchg(pprev, &work, work->next))
139			break;
140	}
141	raw_spin_unlock_irqrestore(&task->pi_lock, flags);
142
143	return work;
144}
145
146static bool task_work_func_match(struct callback_head *cb, void *data)
147{
148	return cb->func == data;
149}
150
151/**
152 * task_work_cancel_func - cancel a pending work matching a function added by task_work_add()
153 * @task: the task which should execute the func's work
154 * @func: identifies the func to match with a work to remove
155 *
156 * Find the last queued pending work with ->func == @func and remove
157 * it from queue.
158 *
159 * RETURNS:
160 * The found work or NULL if not found.
161 */
162struct callback_head *
163task_work_cancel_func(struct task_struct *task, task_work_func_t func)
164{
165	return task_work_cancel_match(task, task_work_func_match, func);
166}
167
168static bool task_work_match(struct callback_head *cb, void *data)
169{
170	return cb == data;
171}
172
173/**
174 * task_work_cancel - cancel a pending work added by task_work_add()
175 * @task: the task which should execute the work
176 * @cb: the callback to remove if queued
177 *
178 * Remove a callback from a task's queue if queued.
179 *
180 * RETURNS:
181 * True if the callback was queued and got cancelled, false otherwise.
182 */
183bool task_work_cancel(struct task_struct *task, struct callback_head *cb)
184{
185	struct callback_head *ret;
186
187	ret = task_work_cancel_match(task, task_work_match, cb);
188
189	return ret == cb;
190}
191
192/**
193 * task_work_run - execute the works added by task_work_add()
194 *
195 * Flush the pending works. Should be used by the core kernel code.
196 * Called before the task returns to the user-mode or stops, or when
197 * it exits. In the latter case task_work_add() can no longer add the
198 * new work after task_work_run() returns.
199 */
200void task_work_run(void)
201{
202	struct task_struct *task = current;
203	struct callback_head *work, *head, *next;
204
205	for (;;) {
206		/*
207		 * work->func() can do task_work_add(), do not set
208		 * work_exited unless the list is empty.
209		 */
210		work = READ_ONCE(task->task_works);
211		do {
212			head = NULL;
213			if (!work) {
214				if (task->flags & PF_EXITING)
215					head = &work_exited;
216				else
217					break;
218			}
219		} while (!try_cmpxchg(&task->task_works, &work, head));
220
221		if (!work)
222			break;
223		/*
224		 * Synchronize with task_work_cancel_match(). It can not remove
225		 * the first entry == work, cmpxchg(task_works) must fail.
226		 * But it can remove another entry from the ->next list.
227		 */
228		raw_spin_lock_irq(&task->pi_lock);
229		raw_spin_unlock_irq(&task->pi_lock);
230
231		do {
232			next = work->next;
233			work->func(work);
234			work = next;
235			cond_resched();
236		} while (work);
237	}
238}