Re: [PATCH v3 2/2] blk-mq: fix blk_mq_tags double free while nr_requests grown

From: Yu Kuai <redacted>

In the case user trigger tags grow by queue sysfs attribute nr_requests,
hctx->sched_tags will be freed directly and replaced with a new
allocated tags, see blk_mq_tag_update_depth().

The problem is that hctx->sched_tags is from elevator->et->tags, while
et->tags is still the freed tags, hence later elevator exit will try to
free the tags again, causing kernel panic.

Fix this problem by replacing et->tags with new allocated tags as well.

Noted there are still some long term problems that will require some
refactor to be fixed thoroughly[1].

[1] https://lore.kernel.org/all/20250815080216.410665-1-yukuai1@huaweicloud.com/ (local)
Fixes: f5a6604f7a44 ("block: fix lockdep warning caused by lock dependency in elv_iosched_store")

Signed-off-by: Yu Kuai <redacted>
Reviewed-by: Ming Lei <redacted>
Reviewed-by: Nilay Shroff<redacted>
---
  block/blk-mq-tag.c | 1 +
  1 file changed, 1 insertion(+)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index d880c50629d6..5cffa5668d0c 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c

@@ -622,6 +622,7 @@ int blk_mq_tag_update_depth(struct blk_mq_hw_ctx *hctx,
  			return -ENOMEM;
  
  		blk_mq_free_map_and_rqs(set, *tagsptr, hctx->queue_num);
+		hctx->queue->elevator->et->tags[hctx->queue_num] = new;
  		*tagsptr = new;
  	} else {
  		/*