kernel/task_work.c

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