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 head = READ_ONCE(task->task_works); 51 do { 52 if (unlikely(head == &work_exited)) 53 return -ESRCH; 54 work->next = head; 55 } while (!try_cmpxchg(&task->task_works, &head, work)); 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 * @data: data to be passed in to match function 82 * 83 * RETURNS: 84 * The found work or NULL if not found. 85 */ 86 struct callback_head * 87 task_work_cancel_match(struct task_struct *task, 88 bool (*match)(struct callback_head *, void *data), 89 void *data) 90 { 91 struct callback_head **pprev = &task->task_works; 92 struct callback_head *work; 93 unsigned long flags; 94 95 if (likely(!task_work_pending(task))) 96 return NULL; 97 /* 98 * If cmpxchg() fails we continue without updating pprev. 99 * Either we raced with task_work_add() which added the 100 * new entry before this work, we will find it again. Or 101 * we raced with task_work_run(), *pprev == NULL/exited. 102 */ 103 raw_spin_lock_irqsave(&task->pi_lock, flags); 104 work = READ_ONCE(*pprev); 105 while (work) { 106 if (!match(work, data)) { 107 pprev = &work->next; 108 work = READ_ONCE(*pprev); 109 } else if (try_cmpxchg(pprev, &work, work->next)) 110 break; 111 } 112 raw_spin_unlock_irqrestore(&task->pi_lock, flags); 113 114 return work; 115 } 116 117 static bool task_work_func_match(struct callback_head *cb, void *data) 118 { 119 return cb->func == data; 120 } 121 122 /** 123 * task_work_cancel - cancel a pending work added by task_work_add() 124 * @task: the task which should execute the work 125 * @func: identifies the work to remove 126 * 127 * Find the last queued pending work with ->func == @func and remove 128 * it from queue. 129 * 130 * RETURNS: 131 * The found work or NULL if not found. 132 */ 133 struct callback_head * 134 task_work_cancel(struct task_struct *task, task_work_func_t func) 135 { 136 return task_work_cancel_match(task, task_work_func_match, func); 137 } 138 139 /** 140 * task_work_run - execute the works added by task_work_add() 141 * 142 * Flush the pending works. Should be used by the core kernel code. 143 * Called before the task returns to the user-mode or stops, or when 144 * it exits. In the latter case task_work_add() can no longer add the 145 * new work after task_work_run() returns. 146 */ 147 void task_work_run(void) 148 { 149 struct task_struct *task = current; 150 struct callback_head *work, *head, *next; 151 152 for (;;) { 153 /* 154 * work->func() can do task_work_add(), do not set 155 * work_exited unless the list is empty. 156 */ 157 work = READ_ONCE(task->task_works); 158 do { 159 head = NULL; 160 if (!work) { 161 if (task->flags & PF_EXITING) 162 head = &work_exited; 163 else 164 break; 165 } 166 } while (!try_cmpxchg(&task->task_works, &work, head)); 167 168 if (!work) 169 break; 170 /* 171 * Synchronize with task_work_cancel(). It can not remove 172 * the first entry == work, cmpxchg(task_works) must fail. 173 * But it can remove another entry from the ->next list. 174 */ 175 raw_spin_lock_irq(&task->pi_lock); 176 raw_spin_unlock_irq(&task->pi_lock); 177 178 do { 179 next = work->next; 180 work->func(work); 181 work = next; 182 cond_resched(); 183 } while (work); 184 } 185 } 186