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 /* 13 * no-op IPI 14 * 15 * TWA_NMI_CURRENT will already have set the TIF flag, all 16 * this interrupt does it tickle the return-to-user path. 17 */ 18 } 19 static DEFINE_PER_CPU(struct irq_work, irq_work_NMI_resume) = 20 IRQ_WORK_INIT_HARD(task_work_set_notify_irq); 21 #endif 22 23 /** 24 * task_work_add - ask the @task to execute @work->func() 25 * @task: the task which should run the callback 26 * @work: the callback to run 27 * @notify: how to notify the targeted task 28 * 29 * Queue @work for task_work_run() below and notify the @task if @notify 30 * is @TWA_RESUME, @TWA_SIGNAL, @TWA_SIGNAL_NO_IPI or @TWA_NMI_CURRENT. 31 * 32 * @TWA_SIGNAL works like signals, in that the it will interrupt the targeted 33 * task and run the task_work, regardless of whether the task is currently 34 * running in the kernel or userspace. 35 * @TWA_SIGNAL_NO_IPI works like @TWA_SIGNAL, except it doesn't send a 36 * reschedule IPI to force the targeted task to reschedule and run task_work. 37 * This can be advantageous if there's no strict requirement that the 38 * task_work be run as soon as possible, just whenever the task enters the 39 * kernel anyway. 40 * @TWA_RESUME work is run only when the task exits the kernel and returns to 41 * user mode, or before entering guest mode. 42 * @TWA_NMI_CURRENT works like @TWA_RESUME, except it can only be used for the 43 * current @task and if the current context is NMI. 44 * 45 * Fails if the @task is exiting/exited and thus it can't process this @work. 46 * Otherwise @work->func() will be called when the @task goes through one of 47 * the aforementioned transitions, or exits. 48 * 49 * If the targeted task is exiting, then an error is returned and the work item 50 * is not queued. It's up to the caller to arrange for an alternative mechanism 51 * in that case. 52 * 53 * Note: there is no ordering guarantee on works queued here. The task_work 54 * list is LIFO. 55 * 56 * RETURNS: 57 * 0 if succeeds or -ESRCH. 58 */ 59 int task_work_add(struct task_struct *task, struct callback_head *work, 60 enum task_work_notify_mode notify) 61 { 62 struct callback_head *head; 63 64 if (notify == TWA_NMI_CURRENT) { 65 if (WARN_ON_ONCE(task != current)) 66 return -EINVAL; 67 if (!IS_ENABLED(CONFIG_IRQ_WORK)) 68 return -EINVAL; 69 } else { 70 kasan_record_aux_stack(work); 71 } 72 73 head = READ_ONCE(task->task_works); 74 do { 75 if (unlikely(head == &work_exited)) 76 return -ESRCH; 77 work->next = head; 78 } while (!try_cmpxchg(&task->task_works, &head, work)); 79 80 switch (notify) { 81 case TWA_NONE: 82 break; 83 case TWA_RESUME: 84 set_notify_resume(task); 85 break; 86 case TWA_SIGNAL: 87 set_notify_signal(task); 88 break; 89 case TWA_SIGNAL_NO_IPI: 90 __set_notify_signal(task); 91 break; 92 #ifdef CONFIG_IRQ_WORK 93 case TWA_NMI_CURRENT: 94 set_tsk_thread_flag(current, TIF_NOTIFY_RESUME); 95 irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume)); 96 break; 97 #endif 98 default: 99 WARN_ON_ONCE(1); 100 break; 101 } 102 103 return 0; 104 } 105 106 /** 107 * task_work_cancel_match - cancel a pending work added by task_work_add() 108 * @task: the task which should execute the work 109 * @match: match function to call 110 * @data: data to be passed in to match function 111 * 112 * RETURNS: 113 * The found work or NULL if not found. 114 */ 115 struct callback_head * 116 task_work_cancel_match(struct task_struct *task, 117 bool (*match)(struct callback_head *, void *data), 118 void *data) 119 { 120 struct callback_head **pprev = &task->task_works; 121 struct callback_head *work; 122 unsigned long flags; 123 124 if (likely(!task_work_pending(task))) 125 return NULL; 126 /* 127 * If cmpxchg() fails we continue without updating pprev. 128 * Either we raced with task_work_add() which added the 129 * new entry before this work, we will find it again. Or 130 * we raced with task_work_run(), *pprev == NULL/exited. 131 */ 132 raw_spin_lock_irqsave(&task->pi_lock, flags); 133 work = READ_ONCE(*pprev); 134 while (work) { 135 if (!match(work, data)) { 136 pprev = &work->next; 137 work = READ_ONCE(*pprev); 138 } else if (try_cmpxchg(pprev, &work, work->next)) 139 break; 140 } 141 raw_spin_unlock_irqrestore(&task->pi_lock, flags); 142 143 return work; 144 } 145 146 static bool task_work_func_match(struct callback_head *cb, void *data) 147 { 148 return cb->func == data; 149 } 150 151 /** 152 * task_work_cancel_func - cancel a pending work matching a function added by task_work_add() 153 * @task: the task which should execute the func's work 154 * @func: identifies the func to match with a work to remove 155 * 156 * Find the last queued pending work with ->func == @func and remove 157 * it from queue. 158 * 159 * RETURNS: 160 * The found work or NULL if not found. 161 */ 162 struct callback_head * 163 task_work_cancel_func(struct task_struct *task, task_work_func_t func) 164 { 165 return task_work_cancel_match(task, task_work_func_match, func); 166 } 167 168 static bool task_work_match(struct callback_head *cb, void *data) 169 { 170 return cb == data; 171 } 172 173 /** 174 * task_work_cancel - cancel a pending work added by task_work_add() 175 * @task: the task which should execute the work 176 * @cb: the callback to remove if queued 177 * 178 * Remove a callback from a task's queue if queued. 179 * 180 * RETURNS: 181 * True if the callback was queued and got cancelled, false otherwise. 182 */ 183 bool task_work_cancel(struct task_struct *task, struct callback_head *cb) 184 { 185 struct callback_head *ret; 186 187 ret = task_work_cancel_match(task, task_work_match, cb); 188 189 return ret == cb; 190 } 191 192 /** 193 * task_work_run - execute the works added by task_work_add() 194 * 195 * Flush the pending works. Should be used by the core kernel code. 196 * Called before the task returns to the user-mode or stops, or when 197 * it exits. In the latter case task_work_add() can no longer add the 198 * new work after task_work_run() returns. 199 */ 200 void task_work_run(void) 201 { 202 struct task_struct *task = current; 203 struct callback_head *work, *head, *next; 204 205 for (;;) { 206 /* 207 * work->func() can do task_work_add(), do not set 208 * work_exited unless the list is empty. 209 */ 210 work = READ_ONCE(task->task_works); 211 do { 212 head = NULL; 213 if (!work) { 214 if (task->flags & PF_EXITING) 215 head = &work_exited; 216 else 217 break; 218 } 219 } while (!try_cmpxchg(&task->task_works, &work, head)); 220 221 if (!work) 222 break; 223 /* 224 * Synchronize with task_work_cancel_match(). It can not remove 225 * the first entry == work, cmpxchg(task_works) must fail. 226 * But it can remove another entry from the ->next list. 227 */ 228 raw_spin_lock_irq(&task->pi_lock); 229 raw_spin_unlock_irq(&task->pi_lock); 230 231 do { 232 next = work->next; 233 work->func(work); 234 work = next; 235 cond_resched(); 236 } while (work); 237 } 238 } 239