linux-kernel - [PATCH 5.4 111/141] blk-mq: Swap two calls in blk_mq_exit

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Message-Id: <20210517140246.538365162@linuxfoundation.org>
Date:   Mon, 17 May 2021 16:02:43 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
        Ming Lei <ming.lei@...hat.com>,
        Hannes Reinecke <hare@...e.com>,
        Bart Van Assche <bvanassche@....org>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 111/141] blk-mq: Swap two calls in blk_mq_exit_queue()

From: Bart Van Assche <bvanassche@....org>

[ Upstream commit 630ef623ed26c18a457cdc070cf24014e50129c2 ]

If a tag set is shared across request queues (e.g. SCSI LUNs) then the
block layer core keeps track of the number of active request queues in
tags->active_queues. blk_mq_tag_busy() and blk_mq_tag_idle() update that
atomic counter if the hctx flag BLK_MQ_F_TAG_QUEUE_SHARED is set. Make
sure that blk_mq_exit_queue() calls blk_mq_tag_idle() before that flag is
cleared by blk_mq_del_queue_tag_set().

Cc: Christoph Hellwig <hch@...radead.org>
Cc: Ming Lei <ming.lei@...hat.com>
Cc: Hannes Reinecke <hare@...e.com>
Fixes: 0d2602ca30e4 ("blk-mq: improve support for shared tags maps")
Signed-off-by: Bart Van Assche <bvanassche@....org>
Reviewed-by: Ming Lei <ming.lei@...hat.com>
Link: https://lore.kernel.org/r/20210513171529.7977-1-bvanassche@acm.org
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 block/blk-mq.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2970,10 +2970,12 @@ EXPORT_SYMBOL(blk_mq_init_allocated_queu
 /* tags can _not_ be used after returning from blk_mq_exit_queue */
 void blk_mq_exit_queue(struct request_queue *q)
 {
-	struct blk_mq_tag_set	*set = q->tag_set;
+	struct blk_mq_tag_set *set = q->tag_set;
 
-	blk_mq_del_queue_tag_set(q);
+	/* Checks hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED. */
 	blk_mq_exit_hw_queues(q, set, set->nr_hw_queues);
+	/* May clear BLK_MQ_F_TAG_QUEUE_SHARED in hctx->flags. */
+	blk_mq_del_queue_tag_set(q);
 }
 
 static int __blk_mq_alloc_rq_maps(struct blk_mq_tag_set *set)