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