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: how to notify the targeted task 13 * 14 * Queue @work for task_work_run() below and notify the @task if @notify 15 * is @TWA_RESUME or @TWA_SIGNAL. @TWA_SIGNAL works like signals, in that the 16 * it will interrupt the targeted task and run the task_work. @TWA_RESUME 17 * work is run only when the task exits the kernel and returns to user mode, 18 * or before entering guest mode. Fails if the @task is exiting/exited and thus 19 * it can't process this @work. Otherwise @work->func() will be called when the 20 * @task goes through one of the aforementioned transitions, or exits. 21 * 22 * If the targeted task is exiting, then an error is returned and the work item 23 * is not queued. It's up to the caller to arrange for an alternative mechanism 24 * in that case. 25 * 26 * Note: there is no ordering guarantee on works queued here. The task_work 27 * list is LIFO. 28 * 29 * RETURNS: 30 * 0 if succeeds or -ESRCH. 31 */ 32 int task_work_add(struct task_struct *task, struct callback_head *work, 33 enum task_work_notify_mode notify) 34 { 35 struct callback_head *head; 36 37 do { 38 head = READ_ONCE(task->task_works); 39 if (unlikely(head == &work_exited)) 40 return -ESRCH; 41 work->next = head; 42 } while (cmpxchg(&task->task_works, head, work) != head); 43 44 switch (notify) { 45 case TWA_NONE: 46 break; 47 case TWA_RESUME: 48 set_notify_resume(task); 49 break; 50 case TWA_SIGNAL: 51 set_notify_signal(task); 52 break; 53 default: 54 WARN_ON_ONCE(1); 55 break; 56 } 57 58 return 0; 59 } 60 61 /** 62 * task_work_cancel - cancel a pending work added by task_work_add() 63 * @task: the task which should execute the work 64 * @func: identifies the work to remove 65 * 66 * Find the last queued pending work with ->func == @func and remove 67 * it from queue. 68 * 69 * RETURNS: 70 * The found work or NULL if not found. 71 */ 72 struct callback_head * 73 task_work_cancel(struct task_struct *task, task_work_func_t func) 74 { 75 struct callback_head **pprev = &task->task_works; 76 struct callback_head *work; 77 unsigned long flags; 78 79 if (likely(!task->task_works)) 80 return NULL; 81 /* 82 * If cmpxchg() fails we continue without updating pprev. 83 * Either we raced with task_work_add() which added the 84 * new entry before this work, we will find it again. Or 85 * we raced with task_work_run(), *pprev == NULL/exited. 86 */ 87 raw_spin_lock_irqsave(&task->pi_lock, flags); 88 while ((work = READ_ONCE(*pprev))) { 89 if (work->func != func) 90 pprev = &work->next; 91 else if (cmpxchg(pprev, work, work->next) == work) 92 break; 93 } 94 raw_spin_unlock_irqrestore(&task->pi_lock, flags); 95 96 return work; 97 } 98 99 /** 100 * task_work_run - execute the works added by task_work_add() 101 * 102 * Flush the pending works. Should be used by the core kernel code. 103 * Called before the task returns to the user-mode or stops, or when 104 * it exits. In the latter case task_work_add() can no longer add the 105 * new work after task_work_run() returns. 106 */ 107 void task_work_run(void) 108 { 109 struct task_struct *task = current; 110 struct callback_head *work, *head, *next; 111 112 for (;;) { 113 /* 114 * work->func() can do task_work_add(), do not set 115 * work_exited unless the list is empty. 116 */ 117 do { 118 head = NULL; 119 work = READ_ONCE(task->task_works); 120 if (!work) { 121 if (task->flags & PF_EXITING) 122 head = &work_exited; 123 else 124 break; 125 } 126 } while (cmpxchg(&task->task_works, work, head) != work); 127 128 if (!work) 129 break; 130 /* 131 * Synchronize with task_work_cancel(). It can not remove 132 * the first entry == work, cmpxchg(task_works) must fail. 133 * But it can remove another entry from the ->next list. 134 */ 135 raw_spin_lock_irq(&task->pi_lock); 136 raw_spin_unlock_irq(&task->pi_lock); 137 138 do { 139 next = work->next; 140 work->func(work); 141 work = next; 142 cond_resched(); 143 } while (work); 144 } 145 } 146