linux-kernel - Re: [PATCH 00/10] blk-mq: fix blk_mq_tags double free while nr

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Message-ID: <aJ7wMFkuTewlyx1P@fedora>
Date: Fri, 15 Aug 2025 16:30:40 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: axboe@...nel.dk, hare@...e.de, nilay@...ux.ibm.com,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	yukuai3@...wei.com, yi.zhang@...wei.com, yangerkun@...wei.com,
	johnny.chenyi@...wei.com
Subject: Re: [PATCH 00/10] blk-mq: fix blk_mq_tags double free while
 nr_requests grown

On Fri, Aug 15, 2025 at 04:02:06PM +0800, 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 exist will try to
> free the tags again, causing kernel panic.
> 
> patch 1-6 are prep cleanup and refactor patches for updating nr_requests
> patch 7,8 are the fix patches for the regression
> patch 9 is cleanup patch after patch 8
> patch 10 fix the stale nr_requests documentation

Please do not mix bug(regression) fix with cleanup.

The bug fix for updating nr_requests should have been simple enough in single
or two patches, why do you make 10-patches for dealing with the regression?

Not mention this way is really unfriendly for stable tree backport.


Thanks,
Ming