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 /* record the work call stack in order to print it in KASAN reports */ 66 kasan_record_aux_stack(work); 67 } 68 69 head = READ_ONCE(task->task_works); 70 do { 71 if (unlikely(head == &work_exited)) 72 return -ESRCH; 73 work->next = head; 74 } while (!try_cmpxchg(&task->task_works, &head, work)); 75 76 switch (notify) { 77 case TWA_NONE: 78 break; 79 case TWA_RESUME: 80 set_notify_resume(task); 81 break; 82 case TWA_SIGNAL: 83 set_notify_signal(task); 84 break; 85 case TWA_SIGNAL_NO_IPI: 86 __set_notify_signal(task); 87 break; 88 #ifdef CONFIG_IRQ_WORK 89 case TWA_NMI_CURRENT: 90 irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume)); 91 break; 92 #endif 93 default: 94 WARN_ON_ONCE(1); 95 break; 96 } 97 98 return 0; 99 } 100 101 /** 102 * task_work_cancel_match - cancel a pending work added by task_work_add() 103 * @task: the task which should execute the work 104 * @match: match function to call 105 * @data: data to be passed in to match function 106 * 107 * RETURNS: 108 * The found work or NULL if not found. 109 */ 110 struct callback_head * 111 task_work_cancel_match(struct task_struct *task, 112 bool (*match)(struct callback_head *, void *data), 113 void *data) 114 { 115 struct callback_head **pprev = &task->task_works; 116 struct callback_head *work; 117 unsigned long flags; 118 119 if (likely(!task_work_pending(task))) 120 return NULL; 121 /* 122 * If cmpxchg() fails we continue without updating pprev. 123 * Either we raced with task_work_add() which added the 124 * new entry before this work, we will find it again. Or 125 * we raced with task_work_run(), *pprev == NULL/exited. 126 */ 127 raw_spin_lock_irqsave(&task->pi_lock, flags); 128 work = READ_ONCE(*pprev); 129 while (work) { 130 if (!match(work, data)) { 131 pprev = &work->next; 132 work = READ_ONCE(*pprev); 133 } else if (try_cmpxchg(pprev, &work, work->next)) 134 break; 135 } 136 raw_spin_unlock_irqrestore(&task->pi_lock, flags); 137 138 return work; 139 } 140 141 static bool task_work_func_match(struct callback_head *cb, void *data) 142 { 143 return cb->func == data; 144 } 145 146 /** 147 * task_work_cancel_func - cancel a pending work matching a function added by task_work_add() 148 * @task: the task which should execute the func's work 149 * @func: identifies the func to match with a work to remove 150 * 151 * Find the last queued pending work with ->func == @func and remove 152 * it from queue. 153 * 154 * RETURNS: 155 * The found work or NULL if not found. 156 */ 157 struct callback_head * 158 task_work_cancel_func(struct task_struct *task, task_work_func_t func) 159 { 160 return task_work_cancel_match(task, task_work_func_match, func); 161 } 162 163 static bool task_work_match(struct callback_head *cb, void *data) 164 { 165 return cb == data; 166 } 167 168 /** 169 * task_work_cancel - cancel a pending work added by task_work_add() 170 * @task: the task which should execute the work 171 * @cb: the callback to remove if queued 172 * 173 * Remove a callback from a task's queue if queued. 174 * 175 * RETURNS: 176 * True if the callback was queued and got cancelled, false otherwise. 177 */ 178 bool task_work_cancel(struct task_struct *task, struct callback_head *cb) 179 { 180 struct callback_head *ret; 181 182 ret = task_work_cancel_match(task, task_work_match, cb); 183 184 return ret == cb; 185 } 186 187 /** 188 * task_work_run - execute the works added by task_work_add() 189 * 190 * Flush the pending works. Should be used by the core kernel code. 191 * Called before the task returns to the user-mode or stops, or when 192 * it exits. In the latter case task_work_add() can no longer add the 193 * new work after task_work_run() returns. 194 */ 195 void task_work_run(void) 196 { 197 struct task_struct *task = current; 198 struct callback_head *work, *head, *next; 199 200 for (;;) { 201 /* 202 * work->func() can do task_work_add(), do not set 203 * work_exited unless the list is empty. 204 */ 205 work = READ_ONCE(task->task_works); 206 do { 207 head = NULL; 208 if (!work) { 209 if (task->flags & PF_EXITING) 210 head = &work_exited; 211 else 212 break; 213 } 214 } while (!try_cmpxchg(&task->task_works, &work, head)); 215 216 if (!work) 217 break; 218 /* 219 * Synchronize with task_work_cancel_match(). It can not remove 220 * the first entry == work, cmpxchg(task_works) must fail. 221 * But it can remove another entry from the ->next list. 222 */ 223 raw_spin_lock_irq(&task->pi_lock); 224 raw_spin_unlock_irq(&task->pi_lock); 225 226 do { 227 next = work->next; 228 work->func(work); 229 work = next; 230 cond_resched(); 231 } while (work); 232 } 233 } 234