[Xenial] blk-mq: really fix plug list flushing for nomerge queues

Thadeu Lima de Souza Cascardo cascardo at canonical.com
Wed Jan 18 10:31:42 UTC 2017


From: Omar Sandoval <osandov at fb.com>

BugLink: https://bugs.launchpad.net/bugs/1657281

Commit 0809e3ac6231 ("block: fix plug list flushing for nomerge queues")
updated blk_mq_make_request() to set request_count even when
blk_queue_nomerges() returns true. However, blk_mq_make_request() only
does limited plugging and doesn't use request_count;
blk_sq_make_request() is the one that should have been fixed. Do that
and get rid of the unnecessary work in the mq version.

Fixes: 0809e3ac6231 ("block: fix plug list flushing for nomerge queues")
Signed-off-by: Omar Sandoval <osandov at fb.com>
Reviewed-by: Ming Lei <tom.leiming at gmail.com>
Reviewed-by: Jeff Moyer <jmoyer at redhat.com>
Signed-off-by: Jens Axboe <axboe at fb.com>
(cherry picked from commit 87c279e613f848c691111b29d49de8df3f4f56da)
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 block/blk-mq.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index ec732f5..1b7a905 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1304,12 +1304,9 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 
 	blk_queue_split(q, &bio, q->bio_split);
 
-	if (!is_flush_fua && !blk_queue_nomerges(q)) {
-		if (blk_attempt_plug_merge(q, bio, &request_count,
-					   &same_queue_rq))
-			return BLK_QC_T_NONE;
-	} else
-		request_count = blk_plug_queued_count(q);
+	if (!is_flush_fua && !blk_queue_nomerges(q) &&
+	    blk_attempt_plug_merge(q, bio, &request_count, &same_queue_rq))
+		return BLK_QC_T_NONE;
 
 	rq = blk_mq_map_request(q, bio, &data);
 	if (unlikely(!rq))
@@ -1400,9 +1397,11 @@ static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
 
 	blk_queue_split(q, &bio, q->bio_split);
 
-	if (!is_flush_fua && !blk_queue_nomerges(q) &&
-	    blk_attempt_plug_merge(q, bio, &request_count, NULL))
-		return BLK_QC_T_NONE;
+	if (!is_flush_fua && !blk_queue_nomerges(q)) {
+		if (blk_attempt_plug_merge(q, bio, &request_count, NULL))
+			return BLK_QC_T_NONE;
+	} else
+		request_count = blk_plug_queued_count(q);
 
 	rq = blk_mq_map_request(q, bio, &data);
 	if (unlikely(!rq))
-- 
2.9.3





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