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 = ACCESS_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 cmpxchg() fails we continue without updating pprev. 62 * Either we raced with task_work_add() which added the 63 * new entry before this work, we will find it again. Or 64 * we raced with task_work_run(), *pprev == NULL/exited. 65 */ 66 raw_spin_lock_irqsave(&task->pi_lock, flags); 67 while ((work = ACCESS_ONCE(*pprev))) { 68 smp_read_barrier_depends(); 69 if (work->func != func) 70 pprev = &work->next; 71 else if (cmpxchg(pprev, work, work->next) == work) 72 break; 73 } 74 raw_spin_unlock_irqrestore(&task->pi_lock, flags); 75 76 return work; 77 } 78 79 /** 80 * task_work_run - execute the works added by task_work_add() 81 * 82 * Flush the pending works. Should be used by the core kernel code. 83 * Called before the task returns to the user-mode or stops, or when 84 * it exits. In the latter case task_work_add() can no longer add the 85 * new work after task_work_run() returns. 86 */ 87 void task_work_run(void) 88 { 89 struct task_struct *task = current; 90 struct callback_head *work, *head, *next; 91 92 for (;;) { 93 /* 94 * work->func() can do task_work_add(), do not set 95 * work_exited unless the list is empty. 96 */ 97 do { 98 work = ACCESS_ONCE(task->task_works); 99 head = !work && (task->flags & PF_EXITING) ? 100 &work_exited : NULL; 101 } while (cmpxchg(&task->task_works, work, head) != work); 102 103 if (!work) 104 break; 105 /* 106 * Synchronize with task_work_cancel(). It can't remove 107 * the first entry == work, cmpxchg(task_works) should 108 * fail, but it can play with *work and other entries. 109 */ 110 raw_spin_unlock_wait(&task->pi_lock); 111 smp_mb(); 112 113 do { 114 next = work->next; 115 work->func(work); 116 work = next; 117 cond_resched(); 118 } while (work); 119 } 120 } 121