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

___wait_event() doesn't really need abort_exclusive_wait(), we can simply
change prepare_to_wait_event() to remove the waiter from q->task_list if
it was interrupted.

This simplifies the code/logic, and this way prepare_to_wait_event() can
have more users, see the next change.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Neil Brown <neilb@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160908164815.GA18801@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
--
 include/linux/wait.h |    7 +------
 kernel/sched/wait.c  |   35 +++++++++++++++++++++++++----------
 2 files changed, 26 insertions(+), 16 deletions(-)

diff --git a/include/linux/wait.h b/include/linux/wait.h
index e4cfd1e..7261dcb 100644 (file)
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -280,12 +280,7 @@ wait_queue_head_t *bit_waitqueue(void *, int);
                                                                        \
                if (___wait_is_interruptible(state) && __int) {         \
                        __ret = __int;                                  \
-                       if (exclusive) {                                \
-                               abort_exclusive_wait(&wq, &__wait,      \
-                                                    NULL);             \
-                               goto __out;                             \
-                       }                                               \
-                       break;                                          \
+                       goto __out;                                     \
                }                                                       \
                                                                        \
                cmd;                                                    \

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);