On 2011-04-13 13:12, Peter Zijlstra wrote:

On Tue, 2011-04-12 at 19:23 -0700, Linus Torvalds wrote:

quoted

 kernel/sched.c |   20 ++++++++++----------
 1 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 48013633d792..a187c3fe027b 100644
--- 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)) 

Right, that cures the preemption problem. The reason I suggested placing
it where it was is that I'd like to keep all things that release
rq->lock in the middle of schedule() in one place, but I guess we can
cure that with some extra comments.

We definitely only want to do it on going to sleep, not preempt events.
So if you are fine with this change, then lets please do that.

Linus, I've got a few other things queued up in the area, I'll add this
and send them off soon. Or feel free to add this one yourself, since you
already did it.


-- 
Jens Axboe