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

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@fb.com>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit 87c279e613f848c691111b29d49de8df3f4f56da)
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Acked-by: Luis Henriques <luis.henriques@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index ec732f508673b2ac143d1aff2c3f02905a7b6cae..1b7a9059a0b7d5ed73c1461b5367b88d18412ce0 100644 (file)
--- 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))