[PATCH 6.4 015/800] blk-mq: dont queue plugged passthrough requests into scheduler

Greg Kroah-Hartman
2023-07-16T19:53:29Z

From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit d97217e7f024bbe9aa62aea070771234c2879358 ]

Passthrough requests should never be queued to the I/O scheduler,
as scheduling these opaque requests doesn't make sense, and I/O
schedulers might require req->bio to be always valid.

We never let passthrough requests insert into the scheduler before
commit 1c2d2fff6dc0 ("block: wire-up support for passthrough plugging"),
restore this behavior even for passthrough requests issued under a plug.

[hch: use blk_mq_insert_requests for passthrough requests,
fix up the commit message and comments]

Reported-by: Guangwu Zhang <guazhang@redhat.com>
Closes: https://lore.kernel.org/linux-block/CAGS2=YosaYaUTEMU3uaf+y=8MqSrhL7sYsJn8EwbaM=76p_4Qg@mail.gmail.com/
Investigated-by: Yu Kuai <yukuai1@huaweicloud.com>
Fixes: 1c2d2fff6dc0 ("block: wire-up support for passthrough plugging")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230518053101.760632-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/blk-mq.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 850bfb844ed2f..c763f0bc66371 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2711,6 +2711,7 @@ static void blk_mq_dispatch_plug_list(struct blk_plug *plug, bool from_sched)
struct request *requeue_list = NULL;
struct request **requeue_lastp = &requeue_list;
unsigned int depth = 0;
+ bool is_passthrough = false;
LIST_HEAD(list);

do {
@@ -2719,7 +2720,9 @@ static void blk_mq_dispatch_plug_list(struct blk_plug *plug, bool from_sched)
if (!this_hctx) {
this_hctx = rq->mq_hctx;
this_ctx = rq->mq_ctx;
- } else if (this_hctx != rq->mq_hctx || this_ctx != rq->mq_ctx) {
+ is_passthrough = blk_rq_is_passthrough(rq);
+ } else if (this_hctx != rq->mq_hctx || this_ctx != rq->mq_ctx ||
+ is_passthrough != blk_rq_is_passthrough(rq)) {
rq_list_add_tail(&requeue_lastp, rq);
continue;
}
@@ -2731,7 +2734,8 @@ static void blk_mq_dispatch_plug_list(struct blk_plug *plug, bool from_sched)
trace_block_unplug(this_hctx->queue, depth, !from_sched);

percpu_ref_get(&this_hctx->queue->q_usage_counter);
- if (this_hctx->queue->elevator) {
+ /* passthrough requests should never be issued to the I/O scheduler */
+ if (this_hctx->queue->elevator && !is_passthrough) {
this_hctx->queue->elevator->type->ops.insert_requests(this_hctx,
&list, 0);
blk_mq_run_hw_queue(this_hctx, from_sched);
--
2.39.2