From 6ae0516b8a50ece5d766be608a305707e0450060 Mon Sep 17 00:00:00 2001 From: Shaohua Li Date: Fri, 16 Dec 2011 14:04:23 +0100 Subject: [PATCH] block, cfq: fix empty queue crash caused by request merge All requests of a queue could be merged to other requests of other queue. Such queue will not have request in it, but it's in service tree. This will cause kernel oops. I encounter a BUG_ON() in cfq_dispatch_request() with next patch, but the issue should exist without the patch. Signed-off-by: Shaohua Li Signed-off-by: Jens Axboe --- block/cfq-iosched.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 4c12869fcf77..3548705b04e4 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1655,6 +1655,8 @@ cfq_merged_requests(struct request_queue *q, struct request *rq, struct request *next) { struct cfq_queue *cfqq = RQ_CFQQ(rq); + struct cfq_data *cfqd = q->elevator->elevator_data; + /* * reposition in fifo if next is older than rq */ @@ -1669,6 +1671,16 @@ cfq_merged_requests(struct request_queue *q, struct request *rq, cfq_remove_request(next); cfq_blkiocg_update_io_merged_stats(&(RQ_CFQG(rq))->blkg, rq_data_dir(next), rq_is_sync(next)); + + cfqq = RQ_CFQQ(next); + /* + * all requests of this queue are merged to other queues, delete it + * from the service tree. If it's the active_queue, + * cfq_dispatch_requests() will choose to expire it or do idle + */ + if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list) && + cfqq != cfqd->active_queue) + cfq_del_cfqq_rr(cfqd, cfqq); } static int cfq_allow_merge(struct request_queue *q, struct request *rq, -- 2.39.2