blk-mq: don't allow merges if turned off for the queue

blk-mq uses BLK_MQ_F_SHOULD_MERGE, as set by the driver at init time,
to determine whether it should merge IO or not. However, this could
also be disabled by the admin, if merging is switched off through
sysfs. So check the general queue state as well before attempting
to merge IO.

Reported-by: Rob Elliott <Elliott@hp.com>
Tested-by: Rob Elliott <Elliott@hp.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index ac8a0413664e67ca435bd82f3ac9cb025c65e494..c9e89a8792e33f5eb723b95fcc9fa7e1a4b5888f 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1068,13 +1068,17 @@ static void blk_mq_bio_to_request(struct request *rq, struct bio *bio)
                blk_account_io_start(rq, 1);
 }
 
+static inline bool hctx_allow_merges(struct blk_mq_hw_ctx *hctx)
+{
+       return (hctx->flags & BLK_MQ_F_SHOULD_MERGE) &&
+               !blk_queue_nomerges(hctx->queue);
+}
+
 static inline bool blk_mq_merge_queue_io(struct blk_mq_hw_ctx *hctx,
                                         struct blk_mq_ctx *ctx,
                                         struct request *rq, struct bio *bio)
 {
-       struct request_queue *q = hctx->queue;
-
-       if (!(hctx->flags & BLK_MQ_F_SHOULD_MERGE)) {
+       if (!hctx_allow_merges(hctx)) {
                blk_mq_bio_to_request(rq, bio);
                spin_lock(&ctx->lock);
 insert_rq:
@@ -1082,6 +1086,8 @@ insert_rq:
                spin_unlock(&ctx->lock);
                return false;
        } else {
+               struct request_queue *q = hctx->queue;
+
                spin_lock(&ctx->lock);
                if (!blk_mq_attempt_merge(q, ctx, bio)) {
                        blk_mq_bio_to_request(rq, bio);