block CFQ: avoid moving request to different queue

request is queued in cfqq->fifo list. Looks it's possible we are moving a
request from one cfqq to another in request merge case. In such case, adjusting
the fifo list order doesn't make sense and is impossible if we don't iterate
the whole fifo list.

My test does hit one case the two cfqq are different, but didn't cause kernel
crash, maybe it's because fifo list isn't used frequently. Anyway, from the
code logic, this is buggy.

I thought we can re-enable the recusive merge logic after this is fixed.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index fb52df9744f5fe411908162fbb02257ca0bc097a..e62e9205b80a8047193cd32a690a0e5d5b689b85 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1973,7 +1973,8 @@ cfq_merged_requests(struct request_queue *q, struct request *rq,
         * reposition in fifo if next is older than rq
         */
        if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
-           time_before(rq_fifo_time(next), rq_fifo_time(rq))) {
+           time_before(rq_fifo_time(next), rq_fifo_time(rq)) &&
+           cfqq == RQ_CFQQ(next)) {
                list_move(&rq->queuelist, &next->queuelist);
                rq_set_fifo_time(rq, rq_fifo_time(next));
        }