1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/spinlock.h> 3 #include <linux/task_work.h> 4 #include <linux/tracehook.h> 5 6 static struct callback_head work_exited; /* all we need is ->next == NULL */ 7 8 /** 9 * task_work_add - ask the @task to execute @work->func() 10 * @task: the task which should run the callback 11 * @work: the callback to run 12 * @notify: send the notification if true 13 * 14 * Queue @work for task_work_run() below and notify the @task if @notify. 15 * Fails if the @task is exiting/exited and thus it can't process this @work. 16 * Otherwise @work->func() will be called when the @task returns from kernel 17 * mode or exits. 18 * 19 * This is like the signal handler which runs in kernel mode, but it doesn't 20 * try to wake up the @task. 21 * 22 * Note: there is no ordering guarantee on works queued here. 23 * 24 * RETURNS: 25 * 0 if succeeds or -ESRCH. 26 */ 27 int 28 task_work_add(struct task_struct *task, struct callback_head *work, bool notify) 29 { 30 struct callback_head *head; 31 32 do { 33 head = READ_ONCE(task->task_works); 34 if (unlikely(head == &work_exited)) 35 return -ESRCH; 36 work->next = head; 37 } while (cmpxchg(&task->task_works, head, work) != head); 38 39 if (notify) 40 set_notify_resume(task); 41 return 0; 42 } 43 44 /** 45 * task_work_cancel - cancel a pending work added by task_work_add() 46 * @task: the task which should execute the work 47 * @func: identifies the work to remove 48 * 49 * Find the last queued pending work with ->func == @func and remove 50 * it from queue. 51 * 52 * RETURNS: 53 * The found work or NULL if not found. 54 */ 55 struct callback_head * 56 task_work_cancel(struct task_struct *task, task_work_func_t func) 57 { 58 struct callback_head **pprev = &task->task_works; 59 struct callback_head *work; 60 unsigned long flags; 61 62 if (likely(!task->task_works)) 63 return NULL; 64 /* 65 * If cmpxchg() fails we continue without updating pprev. 66 * Either we raced with task_work_add() which added the 67 * new entry before this work, we will find it again. Or 68 * we raced with task_work_run(), *pprev == NULL/exited. 69 */ 70 raw_spin_lock_irqsave(&task->pi_lock, flags); 71 while ((work = READ_ONCE(*pprev))) { 72 if (work->func != func) 73 pprev = &work->next; 74 else if (cmpxchg(pprev, work, work->next) == work) 75 break; 76 } 77 raw_spin_unlock_irqrestore(&task->pi_lock, flags); 78 79 return work; 80 } 81 82 /** 83 * task_work_run - execute the works added by task_work_add() 84 * 85 * Flush the pending works. Should be used by the core kernel code. 86 * Called before the task returns to the user-mode or stops, or when 87 * it exits. In the latter case task_work_add() can no longer add the 88 * new work after task_work_run() returns. 89 */ 90 void task_work_run(void) 91 { 92 struct task_struct *task = current; 93 struct callback_head *work, *head, *next; 94 95 for (;;) { 96 /* 97 * work->func() can do task_work_add(), do not set 98 * work_exited unless the list is empty. 99 */ 100 do { 101 head = NULL; 102 work = READ_ONCE(task->task_works); 103 if (!work) { 104 if (task->flags & PF_EXITING) 105 head = &work_exited; 106 else 107 break; 108 } 109 } while (cmpxchg(&task->task_works, work, head) != work); 110 111 if (!work) 112 break; 113 /* 114 * Synchronize with task_work_cancel(). It can not remove 115 * the first entry == work, cmpxchg(task_works) must fail. 116 * But it can remove another entry from the ->next list. 117 */ 118 raw_spin_lock_irq(&task->pi_lock); 119 raw_spin_unlock_irq(&task->pi_lock); 120 121 do { 122 next = work->next; 123 work->func(work); 124 work = next; 125 cond_resched(); 126 } while (work); 127 } 128 } 129