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 4801363..a187c3f 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))