1 #include <linux/spinlock.h> 2 #include <linux/task_work.h> 3 #include <linux/tracehook.h> 4 5 static struct callback_head work_exited; /* all we need is ->next == NULL */ 6 7 /** 8 * task_work_add - ask the @task to execute @work->func() 9 * @task: the task which should run the callback 10 * @work: the callback to run 11 * @notify: send the notification if true 12 * 13 * Queue @work for task_work_run() below and notify the @task if @notify. 14 * Fails if the @task is exiting/exited and thus it can't process this @work. 15 * Otherwise @work->func() will be called when the @task returns from kernel 16 * mode or exits. 17 * 18 * This is like the signal handler which runs in kernel mode, but it doesn't 19 * try to wake up the @task. 20 * 21 * Note: there is no ordering guarantee on works queued here. 22 * 23 * RETURNS: 24 * 0 if succeeds or -ESRCH. 25 */ 26 int 27 task_work_add(struct task_struct *task, struct callback_head *work, bool notify) 28 { 29 struct callback_head *head; 30 31 do { 32 head = READ_ONCE(task->task_works); 33 if (unlikely(head == &work_exited)) 34 return -ESRCH; 35 work->next = head; 36 } while (cmpxchg(&task->task_works, head, work) != head); 37 38 if (notify) 39 set_notify_resume(task); 40 return 0; 41 } 42 43 /** 44 * task_work_cancel - cancel a pending work added by task_work_add() 45 * @task: the task which should execute the work 46 * @func: identifies the work to remove 47 * 48 * Find the last queued pending work with ->func == @func and remove 49 * it from queue. 50 * 51 * RETURNS: 52 * The found work or NULL if not found. 53 */ 54 struct callback_head * 55 task_work_cancel(struct task_struct *task, task_work_func_t func) 56 { 57 struct callback_head **pprev = &task->task_works; 58 struct callback_head *work; 59 unsigned long flags; 60 61 if (likely(!task->task_works)) 62 return NULL; 63 /* 64 * If cmpxchg() fails we continue without updating pprev. 65 * Either we raced with task_work_add() which added the 66 * new entry before this work, we will find it again. Or 67 * we raced with task_work_run(), *pprev == NULL/exited. 68 */ 69 raw_spin_lock_irqsave(&task->pi_lock, flags); 70 while ((work = lockless_dereference(*pprev))) { 71 if (work->func != func) 72 pprev = &work->next; 73 else if (cmpxchg(pprev, work, work->next) == work) 74 break; 75 } 76 raw_spin_unlock_irqrestore(&task->pi_lock, flags); 77 78 return work; 79 } 80 81 /** 82 * task_work_run - execute the works added by task_work_add() 83 * 84 * Flush the pending works. Should be used by the core kernel code. 85 * Called before the task returns to the user-mode or stops, or when 86 * it exits. In the latter case task_work_add() can no longer add the 87 * new work after task_work_run() returns. 88 */ 89 void task_work_run(void) 90 { 91 struct task_struct *task = current; 92 struct callback_head *work, *head, *next; 93 94 for (;;) { 95 /* 96 * work->func() can do task_work_add(), do not set 97 * work_exited unless the list is empty. 98 */ 99 do { 100 work = READ_ONCE(task->task_works); 101 head = !work && (task->flags & PF_EXITING) ? 102 &work_exited : NULL; 103 } while (cmpxchg(&task->task_works, work, head) != work); 104 105 if (!work) 106 break; 107 /* 108 * Synchronize with task_work_cancel(). It can't remove 109 * the first entry == work, cmpxchg(task_works) should 110 * fail, but it can play with *work and other entries. 111 */ 112 raw_spin_unlock_wait(&task->pi_lock); 113 114 do { 115 next = work->next; 116 work->func(work); 117 work = next; 118 cond_resched(); 119 } while (work); 120 } 121 } 122