From: Ming Lei <ming.lei@redhat.com>
Date: Thu, 16 Jun 2022 09:43:59 +0800
Subject: [PATCH] blk-mq: protect q->elevator by ->sysfs_lock in
 blk_mq_elv_switch_none
Git-commit: 5fd7a84a09e640016fe106dd3e992f5210e23dc7
Patch-mainline: v5.19-rc3
References: jsc#PED-1183

elevator can be tore down by sysfs switch interface or disk release, so
hold ->sysfs_lock before referring to q->elevator, then potential
use-after-free can be avoided.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20220616014401.817001-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 block/blk-mq.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 26a7f802d7ee..c13d03b2e17c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4440,12 +4440,14 @@ static bool blk_mq_elv_switch_none(struct list_head *head,
 	if (!qe)
 		return false;
 
+	/* q->elevator needs protection from ->sysfs_lock */
+	mutex_lock(&q->sysfs_lock);
+
 	INIT_LIST_HEAD(&qe->node);
 	qe->q = q;
 	qe->type = q->elevator->type;
 	list_add(&qe->node, head);
 
-	mutex_lock(&q->sysfs_lock);
 	/*
 	 * After elevator_switch_mq, the previous elevator_queue will be
 	 * released by elevator_release. The reference of the io scheduler
-- 
2.35.3