sched/wait: Avoid abort_exclusive_wait() in ___wait_event()

[cascardo/linux.git] / kernel / sched / wait.c

diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index 2bbba01..2612393 100644 (file)
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -199,24 +199,39 @@ EXPORT_SYMBOL(prepare_to_wait_exclusive);
 long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
 {
        unsigned long flags;
-
-       if (signal_pending_state(state, current))
-               return -ERESTARTSYS;
+       long ret = 0;
 
        wait->private = current;
        wait->func = autoremove_wake_function;
 
        spin_lock_irqsave(&q->lock, flags);
-       if (list_empty(&wait->task_list)) {
-               if (wait->flags & WQ_FLAG_EXCLUSIVE)
-                       __add_wait_queue_tail(q, wait);
-               else
-                       __add_wait_queue(q, wait);
+       if (unlikely(signal_pending_state(state, current))) {
+               /*
+                * Exclusive waiter must not fail if it was selected by wakeup,
+                * it should "consume" the condition we were waiting for.
+                *
+                * The caller will recheck the condition and return success if
+                * we were already woken up, we can not miss the event because
+                * wakeup locks/unlocks the same q->lock.
+                *
+                * But we need to ensure that set-condition + wakeup after that
+                * can't see us, it should wake up another exclusive waiter if
+                * we fail.
+                */
+               list_del_init(&wait->task_list);
+               ret = -ERESTARTSYS;
+       } else {
+               if (list_empty(&wait->task_list)) {
+                       if (wait->flags & WQ_FLAG_EXCLUSIVE)
+                               __add_wait_queue_tail(q, wait);
+                       else
+                               __add_wait_queue(q, wait);
+               }
+               set_current_state(state);
        }
-       set_current_state(state);
        spin_unlock_irqrestore(&q->lock, flags);
 
-       return 0;
+       return ret;
 }
 EXPORT_SYMBOL(prepare_to_wait_event);