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authorJens Axboe <jens.axboe@oracle.com>2007-04-25 13:42:27 +0200
committerGreg Kroah-Hartman <gregkh@suse.de>2007-05-01 17:06:03 -0700
commit3720eda544ece8fa5ade8c87e5f2cf2fb05b0ff5 (patch)
treeffd078d3143437b00350f78920df108b0490a32e
parentab02a65798ea8b940ea5645655238c778d4e4765 (diff)
downloadlinux-linaro-stable-3720eda544ece8fa5ade8c87e5f2cf2fb05b0ff5.tar.gz
cfq-iosched: fix alias + front merge bug
There's a really rare and obscure bug in CFQ, that causes a crash in cfq_dispatch_insert() due to rq == NULL. One example of that is seen here: http://lkml.org/lkml/2007/4/15/41 Neil correctly diagnosed the situation for how this can happen, read that analysis here: http://lkml.org/lkml/2007/4/25/57 This looks like it requires md to trigger, even though it should potentially be possible to due with O_DIRECT (at least if you edit the kernel and doctor some of the unplug calls). The fix is to move the ->next_rq update to when we add a request to the rbtree. Then we remove the possibility for a request to exist in the rbtree code, but not have ->next_rq correctly updated. Signed-off-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--block/cfq-iosched.c12
1 files changed, 6 insertions, 6 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 07b706243772..0280fe661cd7 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -462,6 +462,12 @@ static void cfq_add_rq_rb(struct request *rq)
if (!cfq_cfqq_on_rr(cfqq))
cfq_add_cfqq_rr(cfqd, cfqq);
+
+ /*
+ * check if this request is a better next-serve candidate
+ */
+ cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq);
+ BUG_ON(!cfqq->next_rq);
}
static inline void
@@ -1623,12 +1629,6 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
cfqq->meta_pending++;
/*
- * check if this request is a better next-serve candidate)) {
- */
- cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq);
- BUG_ON(!cfqq->next_rq);
-
- /*
* we never wait for an async request and we don't allow preemption
* of an async request. so just return early
*/