block: don't flush plugged IO on forced preemtion scheduling

We really only want to unplug the pending IO when the process actually
goes to sleep.  So move the test for flushing the plug up to the place
where we actually deactivate the task - where we have properly checked
for preemption and for the process really sleeping.

Acked-by: Jens Axboe <jaxboe@fusionio.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/sched.c b/kernel/sched.c
index 48013633d792f4682b0777dd96caf10beb6c8e73..a187c3fe027b58debb8c15d6ec98f76d6eb62b75 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4111,20 +4111,20 @@ need_resched:
                                        try_to_wake_up_local(to_wakeup);
                        }
                        deactivate_task(rq, prev, DEQUEUE_SLEEP);
+
+                       /*
+                        * If we are going to sleep and we have plugged IO queued, make
+                        * sure to submit it to avoid deadlocks.
+                        */
+                       if (blk_needs_flush_plug(prev)) {
+                               raw_spin_unlock(&rq->lock);
+                               blk_flush_plug(prev);
+                               raw_spin_lock(&rq->lock);
+                       }
                }
                switch_count = &prev->nvcsw;
        }
 
-       /*
-        * If we are going to sleep and we have plugged IO queued, make
-        * sure to submit it to avoid deadlocks.
-        */
-       if (prev->state != TASK_RUNNING && blk_needs_flush_plug(prev)) {
-               raw_spin_unlock(&rq->lock);
-               blk_flush_plug(prev);
-               raw_spin_lock(&rq->lock);
-       }
-
        pre_schedule(rq, prev);
 
        if (unlikely(!rq->nr_running))