Patch "blk-mq: don't queue plugged passthrough requests into scheduler" has been added to the 6.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    blk-mq: don't queue plugged passthrough requests into scheduler

to the 6.4-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-don-t-queue-plugged-passthrough-requests-into.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 3c2eaae313aa443f0a732f6dfd4ccaf748dfce48
Author: Ming Lei <ming.lei@xxxxxxxxxx>
Date:   Thu May 18 07:30:59 2023 +0200

    blk-mq: don't queue plugged passthrough requests into scheduler
    
    [ 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@xxxxxxxxxx>
    Closes: https://lore.kernel.org/linux-block/CAGS2=YosaYaUTEMU3uaf+y=8MqSrhL7sYsJn8EwbaM=76p_4Qg@xxxxxxxxxxxxxx/
    Investigated-by: Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>
    Fixes: 1c2d2fff6dc0 ("block: wire-up support for passthrough plugging")
    Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
    Signed-off-by: Christoph Hellwig <hch@xxxxxx>
    Link: https://lore.kernel.org/r/20230518053101.760632-2-hch@xxxxxx
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

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);