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kernel/task_work.c
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#include <linux/spinlock.h> #include <linux/task_work.h> #include <linux/tracehook.h> |
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static struct callback_head work_exited; /* all we need is ->next == NULL */ |
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/** * task_work_add - ask the @task to execute @work->func() * @task: the task which should run the callback * @work: the callback to run * @notify: send the notification if true * * Queue @work for task_work_run() below and notify the @task if @notify. * Fails if the @task is exiting/exited and thus it can't process this @work. * Otherwise @work->func() will be called when the @task returns from kernel * mode or exits. * * This is like the signal handler which runs in kernel mode, but it doesn't * try to wake up the @task. * |
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* Note: there is no ordering guarantee on works queued here. * |
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* RETURNS: * 0 if succeeds or -ESRCH. */ |
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int |
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task_work_add(struct task_struct *task, struct callback_head *work, bool notify) |
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{ |
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struct callback_head *head; |
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do { |
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head = READ_ONCE(task->task_works); |
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if (unlikely(head == &work_exited)) return -ESRCH; |
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work->next = head; } while (cmpxchg(&task->task_works, head, work) != head); |
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if (notify) |
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set_notify_resume(task); |
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return 0; |
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} |
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/** * task_work_cancel - cancel a pending work added by task_work_add() * @task: the task which should execute the work * @func: identifies the work to remove * * Find the last queued pending work with ->func == @func and remove * it from queue. * * RETURNS: * The found work or NULL if not found. */ |
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struct callback_head * |
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task_work_cancel(struct task_struct *task, task_work_func_t func) { |
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struct callback_head **pprev = &task->task_works; |
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struct callback_head *work; |
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unsigned long flags; |
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if (likely(!task->task_works)) return NULL; |
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/* * If cmpxchg() fails we continue without updating pprev. * Either we raced with task_work_add() which added the * new entry before this work, we will find it again. Or |
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* we raced with task_work_run(), *pprev == NULL/exited. |
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*/ |
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raw_spin_lock_irqsave(&task->pi_lock, flags); |
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while ((work = lockless_dereference(*pprev))) { |
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if (work->func != func) pprev = &work->next; else if (cmpxchg(pprev, work, work->next) == work) break; |
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} |
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raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
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return work; |
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} |
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/** * task_work_run - execute the works added by task_work_add() * * Flush the pending works. Should be used by the core kernel code. * Called before the task returns to the user-mode or stops, or when * it exits. In the latter case task_work_add() can no longer add the * new work after task_work_run() returns. */ |
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void task_work_run(void) { struct task_struct *task = current; |
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struct callback_head *work, *head, *next; |
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for (;;) { |
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/* * work->func() can do task_work_add(), do not set * work_exited unless the list is empty. */ do { |
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work = READ_ONCE(task->task_works); |
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head = !work && (task->flags & PF_EXITING) ? &work_exited : NULL; } while (cmpxchg(&task->task_works, work, head) != work); |
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if (!work) break; /* * Synchronize with task_work_cancel(). It can't remove * the first entry == work, cmpxchg(task_works) should * fail, but it can play with *work and other entries. */ raw_spin_unlock_wait(&task->pi_lock); |
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do { next = work->next; work->func(work); work = next; |
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cond_resched(); |
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} while (work); |
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} } |