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 unsigned long flags; 37 38 do { 39 head = READ_ONCE(task->task_works); 40 if (unlikely(head == &work_exited)) 41 return -ESRCH; 42 work->next = head; 43 } while (cmpxchg(&task->task_works, head, work) != head); 44 45 switch (notify) { 46 case TWA_NONE: 47 break; 48 case TWA_RESUME: 49 set_notify_resume(task); 50 break; 51 case TWA_SIGNAL: 52 /* 53 * Only grab the sighand lock if we don't already have some 54 * task_work pending. This pairs with the smp_store_mb() 55 * in get_signal(), see comment there. 56 */ 57 if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) && 58 lock_task_sighand(task, &flags)) { 59 task->jobctl |= JOBCTL_TASK_WORK; 60 signal_wake_up(task, 0); 61 unlock_task_sighand(task, &flags); 62 } 63 break; 64 default: 65 WARN_ON_ONCE(1); 66 break; 67 } 68 69 return 0; 70 } 71 72 /** 73 * task_work_cancel - cancel a pending work added by task_work_add() 74 * @task: the task which should execute the work 75 * @func: identifies the work to remove 76 * 77 * Find the last queued pending work with ->func == @func and remove 78 * it from queue. 79 * 80 * RETURNS: 81 * The found work or NULL if not found. 82 */ 83 struct callback_head * 84 task_work_cancel(struct task_struct *task, task_work_func_t func) 85 { 86 struct callback_head **pprev = &task->task_works; 87 struct callback_head *work; 88 unsigned long flags; 89 90 if (likely(!task->task_works)) 91 return NULL; 92 /* 93 * If cmpxchg() fails we continue without updating pprev. 94 * Either we raced with task_work_add() which added the 95 * new entry before this work, we will find it again. Or 96 * we raced with task_work_run(), *pprev == NULL/exited. 97 */ 98 raw_spin_lock_irqsave(&task->pi_lock, flags); 99 while ((work = READ_ONCE(*pprev))) { 100 if (work->func != func) 101 pprev = &work->next; 102 else if (cmpxchg(pprev, work, work->next) == work) 103 break; 104 } 105 raw_spin_unlock_irqrestore(&task->pi_lock, flags); 106 107 return work; 108 } 109 110 /** 111 * task_work_run - execute the works added by task_work_add() 112 * 113 * Flush the pending works. Should be used by the core kernel code. 114 * Called before the task returns to the user-mode or stops, or when 115 * it exits. In the latter case task_work_add() can no longer add the 116 * new work after task_work_run() returns. 117 */ 118 void task_work_run(void) 119 { 120 struct task_struct *task = current; 121 struct callback_head *work, *head, *next; 122 123 for (;;) { 124 /* 125 * work->func() can do task_work_add(), do not set 126 * work_exited unless the list is empty. 127 */ 128 do { 129 head = NULL; 130 work = READ_ONCE(task->task_works); 131 if (!work) { 132 if (task->flags & PF_EXITING) 133 head = &work_exited; 134 else 135 break; 136 } 137 } while (cmpxchg(&task->task_works, work, head) != work); 138 139 if (!work) 140 break; 141 /* 142 * Synchronize with task_work_cancel(). It can not remove 143 * the first entry == work, cmpxchg(task_works) must fail. 144 * But it can remove another entry from the ->next list. 145 */ 146 raw_spin_lock_irq(&task->pi_lock); 147 raw_spin_unlock_irq(&task->pi_lock); 148 149 do { 150 next = work->next; 151 work->func(work); 152 work = next; 153 cond_resched(); 154 } while (work); 155 } 156 } 157