linux-kernel - Re: [PATCH v3 2/2] blk-mq: fix blk_mq_tags double free while nr

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Message-ID: <00421980-4602-4fe4-9f54-1345a7709d71@suse.de>
Date: Fri, 22 Aug 2025 08:02:08 +0200
From: Hannes Reinecke <hare@...e.de>
To: Yu Kuai <yukuai1@...weicloud.com>, yukuai3@...wei.com, axboe@...nel.dk,
 bvanassche@....org, ming.lei@...hat.com, nilay@...ux.ibm.com
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 yi.zhang@...wei.com, yangerkun@...wei.com, johnny.chenyi@...wei.com
Subject: Re: [PATCH v3 2/2] blk-mq: fix blk_mq_tags double free while
 nr_requests grown

On 8/21/25 08:06, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@...wei.com>
> 
> 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/
> Fixes: f5a6604f7a44 ("block: fix lockdep warning caused by lock dependency in elv_iosched_store")
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> Reviewed-by: Ming Lei <ming.lei@...hat.com>
> Reviewed-by: Nilay Shroff<nilay@...ux.ibm.com>
> ---
>   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 {
>   		/*

Reviewed-by: Hannes Reinecke <hare@...e.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich