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, int notify) 29 { 30 struct callback_head *head; 31 unsigned long flags; 32 33 do { 34 head = READ_ONCE(task->task_works); 35 if (unlikely(head == &work_exited)) 36 return -ESRCH; 37 work->next = head; 38 } while (cmpxchg(&task->task_works, head, work) != head); 39 40 switch (notify) { 41 case TWA_RESUME: 42 set_notify_resume(task); 43 break; 44 case TWA_SIGNAL: 45 if (lock_task_sighand(task, &flags)) { 46 task->jobctl |= JOBCTL_TASK_WORK; 47 signal_wake_up(task, 0); 48 unlock_task_sighand(task, &flags); 49 } 50 break; 51 } 52 53 return 0; 54 } 55 56 /** 57 * task_work_cancel - cancel a pending work added by task_work_add() 58 * @task: the task which should execute the work 59 * @func: identifies the work to remove 60 * 61 * Find the last queued pending work with ->func == @func and remove 62 * it from queue. 63 * 64 * RETURNS: 65 * The found work or NULL if not found. 66 */ 67 struct callback_head * 68 task_work_cancel(struct task_struct *task, task_work_func_t func) 69 { 70 struct callback_head **pprev = &task->task_works; 71 struct callback_head *work; 72 unsigned long flags; 73 74 if (likely(!task->task_works)) 75 return NULL; 76 /* 77 * If cmpxchg() fails we continue without updating pprev. 78 * Either we raced with task_work_add() which added the 79 * new entry before this work, we will find it again. Or 80 * we raced with task_work_run(), *pprev == NULL/exited. 81 */ 82 raw_spin_lock_irqsave(&task->pi_lock, flags); 83 while ((work = READ_ONCE(*pprev))) { 84 if (work->func != func) 85 pprev = &work->next; 86 else if (cmpxchg(pprev, work, work->next) == work) 87 break; 88 } 89 raw_spin_unlock_irqrestore(&task->pi_lock, flags); 90 91 return work; 92 } 93 94 /** 95 * task_work_run - execute the works added by task_work_add() 96 * 97 * Flush the pending works. Should be used by the core kernel code. 98 * Called before the task returns to the user-mode or stops, or when 99 * it exits. In the latter case task_work_add() can no longer add the 100 * new work after task_work_run() returns. 101 */ 102 void task_work_run(void) 103 { 104 struct task_struct *task = current; 105 struct callback_head *work, *head, *next; 106 107 for (;;) { 108 /* 109 * work->func() can do task_work_add(), do not set 110 * work_exited unless the list is empty. 111 */ 112 do { 113 head = NULL; 114 work = READ_ONCE(task->task_works); 115 if (!work) { 116 if (task->flags & PF_EXITING) 117 head = &work_exited; 118 else 119 break; 120 } 121 } while (cmpxchg(&task->task_works, work, head) != work); 122 123 if (!work) 124 break; 125 /* 126 * Synchronize with task_work_cancel(). It can not remove 127 * the first entry == work, cmpxchg(task_works) must fail. 128 * But it can remove another entry from the ->next list. 129 */ 130 raw_spin_lock_irq(&task->pi_lock); 131 raw_spin_unlock_irq(&task->pi_lock); 132 133 do { 134 next = work->next; 135 work->func(work); 136 work = next; 137 cond_resched(); 138 } while (work); 139 } 140 } 141