linux-kernel - Re: [PATCH 1/2] blk-stat: fix QUEUE_FLAG

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Message-ID: <ZDbmlYIrRpkWRZla@slm.duckdns.org>
Date:   Wed, 12 Apr 2023 07:12:53 -1000
From:   Tejun Heo <tj@...nel.org>
To:     chengming.zhou@...ux.dev
Cc:     axboe@...nel.dk, josef@...icpanda.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        Chengming Zhou <zhouchengming@...edance.com>
Subject: Re: [PATCH 1/2] blk-stat: fix QUEUE_FLAG_STATS clear

On Thu, Apr 13, 2023 at 12:07:53AM +0800, chengming.zhou@...ux.dev wrote:
> From: Chengming Zhou <zhouchengming@...edance.com>
> 
> We need to set QUEUE_FLAG_STATS for two cases:
> 1. blk_stat_enable_accounting()
> 2. blk_stat_add_callback()
> 
> So we should clear it only when ((q->stats->accounting == 0) &&
> list_empty(&q->stats->callbacks)).
> 
> blk_stat_disable_accounting() only check if q->stats->accounting
> is 0 before clear the flag, this patch fix it.
> 
> Also add list_empty(&q->stats->callbacks)) check when enable, or
> the flag is already set.
> 
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>

Acked-by: Tejun Heo <tj@...nel.org>

It'd be useful to explicitly illustrate the buggy behavior in the
description (e.g. if you do X, Y and then Z, then X incorrectly loses
accounting). Can you also please add the appropriate stable cc?

Thanks.

-- 
tejun