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, @TWA_SIGNAL, or @TWA_SIGNAL_NO_IPI. 16 * 17 * @TWA_SIGNAL works like signals, in that the it will interrupt the targeted 18 * task and run the task_work, regardless of whether the task is currently 19 * running in the kernel or userspace. 20 * @TWA_SIGNAL_NO_IPI works like @TWA_SIGNAL, except it doesn't send a 21 * reschedule IPI to force the targeted task to reschedule and run task_work. 22 * This can be advantageous if there's no strict requirement that the 23 * task_work be run as soon as possible, just whenever the task enters the 24 * kernel anyway. 25 * @TWA_RESUME work is run only when the task exits the kernel and returns to 26 * user mode, or before entering guest mode. 27 * 28 * Fails if the @task is exiting/exited and thus it can't process this @work. 29 * Otherwise @work->func() will be called when the @task goes through one of 30 * the aforementioned transitions, or exits. 31 * 32 * If the targeted task is exiting, then an error is returned and the work item 33 * is not queued. It's up to the caller to arrange for an alternative mechanism 34 * in that case. 35 * 36 * Note: there is no ordering guarantee on works queued here. The task_work 37 * list is LIFO. 38 * 39 * RETURNS: 40 * 0 if succeeds or -ESRCH. 41 */ 42 int task_work_add(struct task_struct *task, struct callback_head *work, 43 enum task_work_notify_mode notify) 44 { 45 struct callback_head *head; 46 47 /* record the work call stack in order to print it in KASAN reports */ 48 kasan_record_aux_stack(work); 49 50 do { 51 head = READ_ONCE(task->task_works); 52 if (unlikely(head == &work_exited)) 53 return -ESRCH; 54 work->next = head; 55 } while (cmpxchg(&task->task_works, head, work) != head); 56 57 switch (notify) { 58 case TWA_NONE: 59 break; 60 case TWA_RESUME: 61 set_notify_resume(task); 62 break; 63 case TWA_SIGNAL: 64 set_notify_signal(task); 65 break; 66 case TWA_SIGNAL_NO_IPI: 67 __set_notify_signal(task); 68 break; 69 default: 70 WARN_ON_ONCE(1); 71 break; 72 } 73 74 return 0; 75 } 76 77 /** 78 * task_work_cancel_match - cancel a pending work added by task_work_add() 79 * @task: the task which should execute the work 80 * @match: match function to call 81 * 82 * RETURNS: 83 * The found work or NULL if not found. 84 */ 85 struct callback_head * 86 task_work_cancel_match(struct task_struct *task, 87 bool (*match)(struct callback_head *, void *data), 88 void *data) 89 { 90 struct callback_head **pprev = &task->task_works; 91 struct callback_head *work; 92 unsigned long flags; 93 94 if (likely(!task_work_pending(task))) 95 return NULL; 96 /* 97 * If cmpxchg() fails we continue without updating pprev. 98 * Either we raced with task_work_add() which added the 99 * new entry before this work, we will find it again. Or 100 * we raced with task_work_run(), *pprev == NULL/exited. 101 */ 102 raw_spin_lock_irqsave(&task->pi_lock, flags); 103 while ((work = READ_ONCE(*pprev))) { 104 if (!match(work, data)) 105 pprev = &work->next; 106 else if (cmpxchg(pprev, work, work->next) == work) 107 break; 108 } 109 raw_spin_unlock_irqrestore(&task->pi_lock, flags); 110 111 return work; 112 } 113 114 static bool task_work_func_match(struct callback_head *cb, void *data) 115 { 116 return cb->func == data; 117 } 118 119 /** 120 * task_work_cancel - cancel a pending work added by task_work_add() 121 * @task: the task which should execute the work 122 * @func: identifies the work to remove 123 * 124 * Find the last queued pending work with ->func == @func and remove 125 * it from queue. 126 * 127 * RETURNS: 128 * The found work or NULL if not found. 129 */ 130 struct callback_head * 131 task_work_cancel(struct task_struct *task, task_work_func_t func) 132 { 133 return task_work_cancel_match(task, task_work_func_match, func); 134 } 135 136 /** 137 * task_work_run - execute the works added by task_work_add() 138 * 139 * Flush the pending works. Should be used by the core kernel code. 140 * Called before the task returns to the user-mode or stops, or when 141 * it exits. In the latter case task_work_add() can no longer add the 142 * new work after task_work_run() returns. 143 */ 144 void task_work_run(void) 145 { 146 struct task_struct *task = current; 147 struct callback_head *work, *head, *next; 148 149 for (;;) { 150 /* 151 * work->func() can do task_work_add(), do not set 152 * work_exited unless the list is empty. 153 */ 154 do { 155 head = NULL; 156 work = READ_ONCE(task->task_works); 157 if (!work) { 158 if (task->flags & PF_EXITING) 159 head = &work_exited; 160 else 161 break; 162 } 163 } while (cmpxchg(&task->task_works, work, head) != work); 164 165 if (!work) 166 break; 167 /* 168 * Synchronize with task_work_cancel(). It can not remove 169 * the first entry == work, cmpxchg(task_works) must fail. 170 * But it can remove another entry from the ->next list. 171 */ 172 raw_spin_lock_irq(&task->pi_lock); 173 raw_spin_unlock_irq(&task->pi_lock); 174 175 do { 176 next = work->next; 177 work->func(work); 178 work = next; 179 cond_resched(); 180 } while (work); 181 } 182 } 183