This is a note to let you know that I've just added the patch titled blk-mq: really fix plug list flushing for nomerge queues to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: blk-mq-really-fix-plug-list-flushing-for-nomerge-queues.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 87c279e613f848c691111b29d49de8df3f4f56da Mon Sep 17 00:00:00 2001 From: Omar Sandoval <osandov@xxxxxx> Date: Wed, 1 Jun 2016 22:18:48 -0700 Subject: blk-mq: really fix plug list flushing for nomerge queues From: Omar Sandoval <osandov@xxxxxx> commit 87c279e613f848c691111b29d49de8df3f4f56da upstream. 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@xxxxxx> Reviewed-by: Ming Lei <tom.leiming@xxxxxxxxx> Reviewed-by: Jeff Moyer <jmoyer@xxxxxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxx> Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- block/blk-mq.c | 17 ++++++++--------- 1 file changed, 8 insertions(+), 9 deletions(-) --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1259,12 +1259,9 @@ static blk_qc_t blk_mq_make_request(stru 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)) @@ -1355,9 +1352,11 @@ static blk_qc_t blk_sq_make_request(stru 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)) Patches currently in stable-queue which might be from osandov@xxxxxx are queue-4.4/blk-mq-really-fix-plug-list-flushing-for-nomerge-queues.patch