1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/irq_work.h> 3 #include <linux/spinlock.h> 4 #include <linux/task_work.h> 5 #include <linux/resume_user_mode.h> 6 7 static struct callback_head work_exited; /* all we need is ->next == NULL */ 8 9 #ifdef CONFIG_IRQ_WORK 10 static void task_work_set_notify_irq(struct irq_work *entry) 11 { 12 test_and_set_tsk_thread_flag(current, TIF_NOTIFY_RESUME); 13 } 14 static DEFINE_PER_CPU(struct irq_work, irq_work_NMI_resume) = 15 IRQ_WORK_INIT_HARD(task_work_set_notify_irq); 16 #endif 17 18 /** 19 * task_work_add - ask the @task to execute @work->func() 20 * @task: the task which should run the callback 21 * @work: the callback to run 22 * @notify: how to notify the targeted task 23 * 24 * Queue @work for task_work_run() below and notify the @task if @notify 25 * is @TWA_RESUME, @TWA_SIGNAL, @TWA_SIGNAL_NO_IPI or @TWA_NMI_CURRENT. 26 * 27 * @TWA_SIGNAL works like signals, in that the it will interrupt the targeted 28 * task and run the task_work, regardless of whether the task is currently 29 * running in the kernel or userspace. 30 * @TWA_SIGNAL_NO_IPI works like @TWA_SIGNAL, except it doesn't send a 31 * reschedule IPI to force the targeted task to reschedule and run task_work. 32 * This can be advantageous if there's no strict requirement that the 33 * task_work be run as soon as possible, just whenever the task enters the 34 * kernel anyway. 35 * @TWA_RESUME work is run only when the task exits the kernel and returns to 36 * user mode, or before entering guest mode. 37 * @TWA_NMI_CURRENT works like @TWA_RESUME, except it can only be used for the 38 * current @task and if the current context is NMI. 39 * 40 * Fails if the @task is exiting/exited and thus it can't process this @work. 41 * Otherwise @work->func() will be called when the @task goes through one of 42 * the aforementioned transitions, or exits. 43 * 44 * If the targeted task is exiting, then an error is returned and the work item 45 * is not queued. It's up to the caller to arrange for an alternative mechanism 46 * in that case. 47 * 48 * Note: there is no ordering guarantee on works queued here. The task_work 49 * list is LIFO. 50 * 51 * RETURNS: 52 * 0 if succeeds or -ESRCH. 53 */ 54 int task_work_add(struct task_struct *task, struct callback_head *work, 55 enum task_work_notify_mode notify) 56 { 57 struct callback_head *head; 58 59 if (notify == TWA_NMI_CURRENT) { 60 if (WARN_ON_ONCE(task != current)) 61 return -EINVAL; 62 if (!IS_ENABLED(CONFIG_IRQ_WORK)) 63 return -EINVAL; 64 } else { 65 kasan_record_aux_stack(work); 66 } 67 68 head = READ_ONCE(task->task_works); 69 do { 70 if (unlikely(head == &work_exited)) 71 return -ESRCH; 72 work->next = head; 73 } while (!try_cmpxchg(&task->task_works, &head, work)); 74 75 switch (notify) { 76 case TWA_NONE: 77 break; 78 case TWA_RESUME: 79 set_notify_resume(task); 80 break; 81 case TWA_SIGNAL: 82 set_notify_signal(task); 83 break; 84 case TWA_SIGNAL_NO_IPI: 85 __set_notify_signal(task); 86 break; 87 #ifdef CONFIG_IRQ_WORK 88 case TWA_NMI_CURRENT: 89 irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume)); 90 break; 91 #endif 92 default: 93 WARN_ON_ONCE(1); 94 break; 95 } 96 97 return 0; 98 } 99 100 /** 101 * task_work_cancel_match - cancel a pending work added by task_work_add() 102 * @task: the task which should execute the work 103 * @match: match function to call 104 * @data: data to be passed in to match function 105 * 106 * RETURNS: 107 * The found work or NULL if not found. 108 */ 109 struct callback_head * 110 task_work_cancel_match(struct task_struct *task, 111 bool (*match)(struct callback_head *, void *data), 112 void *data) 113 { 114 struct callback_head **pprev = &task->task_works; 115 struct callback_head *work; 116 unsigned long flags; 117 118 if (likely(!task_work_pending(task))) 119 return NULL; 120 /* 121 * If cmpxchg() fails we continue without updating pprev. 122 * Either we raced with task_work_add() which added the 123 * new entry before this work, we will find it again. Or 124 * we raced with task_work_run(), *pprev == NULL/exited. 125 */ 126 raw_spin_lock_irqsave(&task->pi_lock, flags); 127 work = READ_ONCE(*pprev); 128 while (work) { 129 if (!match(work, data)) { 130 pprev = &work->next; 131 work = READ_ONCE(*pprev); 132 } else if (try_cmpxchg(pprev, &work, work->next)) 133 break; 134 } 135 raw_spin_unlock_irqrestore(&task->pi_lock, flags); 136 137 return work; 138 } 139 140 static bool task_work_func_match(struct callback_head *cb, void *data) 141 { 142 return cb->func == data; 143 } 144 145 /** 146 * task_work_cancel_func - cancel a pending work matching a function added by task_work_add() 147 * @task: the task which should execute the func's work 148 * @func: identifies the func to match with a work to remove 149 * 150 * Find the last queued pending work with ->func == @func and remove 151 * it from queue. 152 * 153 * RETURNS: 154 * The found work or NULL if not found. 155 */ 156 struct callback_head * 157 task_work_cancel_func(struct task_struct *task, task_work_func_t func) 158 { 159 return task_work_cancel_match(task, task_work_func_match, func); 160 } 161 162 static bool task_work_match(struct callback_head *cb, void *data) 163 { 164 return cb == data; 165 } 166 167 /** 168 * task_work_cancel - cancel a pending work added by task_work_add() 169 * @task: the task which should execute the work 170 * @cb: the callback to remove if queued 171 * 172 * Remove a callback from a task's queue if queued. 173 * 174 * RETURNS: 175 * True if the callback was queued and got cancelled, false otherwise. 176 */ 177 bool task_work_cancel(struct task_struct *task, struct callback_head *cb) 178 { 179 struct callback_head *ret; 180 181 ret = task_work_cancel_match(task, task_work_match, cb); 182 183 return ret == cb; 184 } 185 186 /** 187 * task_work_run - execute the works added by task_work_add() 188 * 189 * Flush the pending works. Should be used by the core kernel code. 190 * Called before the task returns to the user-mode or stops, or when 191 * it exits. In the latter case task_work_add() can no longer add the 192 * new work after task_work_run() returns. 193 */ 194 void task_work_run(void) 195 { 196 struct task_struct *task = current; 197 struct callback_head *work, *head, *next; 198 199 for (;;) { 200 /* 201 * work->func() can do task_work_add(), do not set 202 * work_exited unless the list is empty. 203 */ 204 work = READ_ONCE(task->task_works); 205 do { 206 head = NULL; 207 if (!work) { 208 if (task->flags & PF_EXITING) 209 head = &work_exited; 210 else 211 break; 212 } 213 } while (!try_cmpxchg(&task->task_works, &work, head)); 214 215 if (!work) 216 break; 217 /* 218 * Synchronize with task_work_cancel_match(). It can not remove 219 * the first entry == work, cmpxchg(task_works) must fail. 220 * But it can remove another entry from the ->next list. 221 */ 222 raw_spin_lock_irq(&task->pi_lock); 223 raw_spin_unlock_irq(&task->pi_lock); 224 225 do { 226 next = work->next; 227 work->func(work); 228 work = next; 229 cond_resched(); 230 } while (work); 231 } 232 } 233