1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/spinlock.h> 3 #include <linux/task_work.h> 4 #include <linux/resume_user_mode.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 /* record the work call stack in order to print it in KASAN reports */ 38 kasan_record_aux_stack(work); 39 40 do { 41 head = READ_ONCE(task->task_works); 42 if (unlikely(head == &work_exited)) 43 return -ESRCH; 44 work->next = head; 45 } while (cmpxchg(&task->task_works, head, work) != head); 46 47 switch (notify) { 48 case TWA_NONE: 49 break; 50 case TWA_RESUME: 51 set_notify_resume(task); 52 break; 53 case TWA_SIGNAL: 54 set_notify_signal(task); 55 break; 56 default: 57 WARN_ON_ONCE(1); 58 break; 59 } 60 61 return 0; 62 } 63 64 /** 65 * task_work_cancel_match - cancel a pending work added by task_work_add() 66 * @task: the task which should execute the work 67 * @match: match function to call 68 * 69 * RETURNS: 70 * The found work or NULL if not found. 71 */ 72 struct callback_head * 73 task_work_cancel_match(struct task_struct *task, 74 bool (*match)(struct callback_head *, void *data), 75 void *data) 76 { 77 struct callback_head **pprev = &task->task_works; 78 struct callback_head *work; 79 unsigned long flags; 80 81 if (likely(!task_work_pending(task))) 82 return NULL; 83 /* 84 * If cmpxchg() fails we continue without updating pprev. 85 * Either we raced with task_work_add() which added the 86 * new entry before this work, we will find it again. Or 87 * we raced with task_work_run(), *pprev == NULL/exited. 88 */ 89 raw_spin_lock_irqsave(&task->pi_lock, flags); 90 while ((work = READ_ONCE(*pprev))) { 91 if (!match(work, data)) 92 pprev = &work->next; 93 else if (cmpxchg(pprev, work, work->next) == work) 94 break; 95 } 96 raw_spin_unlock_irqrestore(&task->pi_lock, flags); 97 98 return work; 99 } 100 101 static bool task_work_func_match(struct callback_head *cb, void *data) 102 { 103 return cb->func == data; 104 } 105 106 /** 107 * task_work_cancel - cancel a pending work added by task_work_add() 108 * @task: the task which should execute the work 109 * @func: identifies the work to remove 110 * 111 * Find the last queued pending work with ->func == @func and remove 112 * it from queue. 113 * 114 * RETURNS: 115 * The found work or NULL if not found. 116 */ 117 struct callback_head * 118 task_work_cancel(struct task_struct *task, task_work_func_t func) 119 { 120 return task_work_cancel_match(task, task_work_func_match, func); 121 } 122 123 /** 124 * task_work_run - execute the works added by task_work_add() 125 * 126 * Flush the pending works. Should be used by the core kernel code. 127 * Called before the task returns to the user-mode or stops, or when 128 * it exits. In the latter case task_work_add() can no longer add the 129 * new work after task_work_run() returns. 130 */ 131 void task_work_run(void) 132 { 133 struct task_struct *task = current; 134 struct callback_head *work, *head, *next; 135 136 for (;;) { 137 /* 138 * work->func() can do task_work_add(), do not set 139 * work_exited unless the list is empty. 140 */ 141 do { 142 head = NULL; 143 work = READ_ONCE(task->task_works); 144 if (!work) { 145 if (task->flags & PF_EXITING) 146 head = &work_exited; 147 else 148 break; 149 } 150 } while (cmpxchg(&task->task_works, work, head) != work); 151 152 if (!work) 153 break; 154 /* 155 * Synchronize with task_work_cancel(). It can not remove 156 * the first entry == work, cmpxchg(task_works) must fail. 157 * But it can remove another entry from the ->next list. 158 */ 159 raw_spin_lock_irq(&task->pi_lock); 160 raw_spin_unlock_irq(&task->pi_lock); 161 162 do { 163 next = work->next; 164 work->func(work); 165 work = next; 166 cond_resched(); 167 } while (work); 168 } 169 } 170