[PATCH] CFQ io scheduler: scheduler switch oops

If cfq is managing a queue and a new scheduler is later selected, it is
possible for the cfqd unplug_work work to be queued after the kblockd
work struct has been flushed.  The problem is the ordering of
cfq_shutdown_timer_wq() and blk_put_queue() in cfq_put_cfqd().  The
latter may rearm the work, leaving cfq_kick_queue() with dead data.

Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/block/cfq-iosched.c b/drivers/block/cfq-iosched.c
index 1ecb179b8604..ff1cc968f96d 100644
--- a/drivers/block/cfq-iosched.c
+++ b/drivers/block/cfq-iosched.c
@@ -2249,10 +2249,11 @@ static void cfq_put_cfqd(struct cfq_data *cfqd)
         if (!atomic_dec_and_test(&cfqd->ref))
                 return;
 
-        cfq_shutdown_timer_wq(cfqd);
-
         blk_put_queue(q);
 
+        cfq_shutdown_timer_wq(cfqd);
+        q->elevator->elevator_data = NULL;
+
         mempool_destroy(cfqd->crq_pool);
         kfree(cfqd->crq_hash);
         kfree(cfqd->cfq_hash);