From: Jens Axboe Date: Wed, 25 Apr 2007 11:42:27 +0000 (+0200) Subject: cfq-iosched: fix alias + front merge bug X-Git-Tag: v2.6.20.11~2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3720eda544ece8fa5ade8c87e5f2cf2fb05b0ff5;p=thirdparty%2Fkernel%2Fstable.git 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 Signed-off-by: Greg Kroah-Hartman --- diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 07b706243772e..0280fe661cd75 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 @@ -1622,12 +1628,6 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq, if (rq_is_meta(rq)) 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