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_match - cancel a pending work added by task_work_add() 63 * @task: the task which should execute the work 64 * @match: match function to call 65 * 66 * RETURNS: 67 * The found work or NULL if not found. 68 */ 69 struct callback_head * 70 task_work_cancel_match(struct task_struct *task, 71 bool (*match)(struct callback_head *, void *data), 72 void *data) 73 { 74 struct callback_head **pprev = &task->task_works; 75 struct callback_head *work; 76 unsigned long flags; 77 78 if (likely(!task->task_works)) 79 return NULL; 80 /* 81 * If cmpxchg() fails we continue without updating pprev. 82 * Either we raced with task_work_add() which added the 83 * new entry before this work, we will find it again. Or 84 * we raced with task_work_run(), *pprev == NULL/exited. 85 */ 86 raw_spin_lock_irqsave(&task->pi_lock, flags); 87 while ((work = READ_ONCE(*pprev))) { 88 if (!match(work, data)) 89 pprev = &work->next; 90 else if (cmpxchg(pprev, work, work->next) == work) 91 break; 92 } 93 raw_spin_unlock_irqrestore(&task->pi_lock, flags); 94 95 return work; 96 } 97 98 static bool task_work_func_match(struct callback_head *cb, void *data) 99 { 100 return cb->func == data; 101 } 102 103 /** 104 * task_work_cancel - cancel a pending work added by task_work_add() 105 * @task: the task which should execute the work 106 * @func: identifies the work to remove 107 * 108 * Find the last queued pending work with ->func == @func and remove 109 * it from queue. 110 * 111 * RETURNS: 112 * The found work or NULL if not found. 113 */ 114 struct callback_head * 115 task_work_cancel(struct task_struct *task, task_work_func_t func) 116 { 117 return task_work_cancel_match(task, task_work_func_match, func); 118 } 119 120 /** 121 * task_work_run - execute the works added by task_work_add() 122 * 123 * Flush the pending works. Should be used by the core kernel code. 124 * Called before the task returns to the user-mode or stops, or when 125 * it exits. In the latter case task_work_add() can no longer add the 126 * new work after task_work_run() returns. 127 */ 128 void task_work_run(void) 129 { 130 struct task_struct *task = current; 131 struct callback_head *work, *head, *next; 132 133 for (;;) { 134 /* 135 * work->func() can do task_work_add(), do not set 136 * work_exited unless the list is empty. 137 */ 138 do { 139 head = NULL; 140 work = READ_ONCE(task->task_works); 141 if (!work) { 142 if (task->flags & PF_EXITING) 143 head = &work_exited; 144 else 145 break; 146 } 147 } while (cmpxchg(&task->task_works, work, head) != work); 148 149 if (!work) 150 break; 151 /* 152 * Synchronize with task_work_cancel(). It can not remove 153 * the first entry == work, cmpxchg(task_works) must fail. 154 * But it can remove another entry from the ->next list. 155 */ 156 raw_spin_lock_irq(&task->pi_lock); 157 raw_spin_unlock_irq(&task->pi_lock); 158 159 do { 160 next = work->next; 161 work->func(work); 162 work = next; 163 cond_resched(); 164 } while (work); 165 } 166 } 167