linux-kernel - Re: [PATCH] mm: fs: fix lru_cache_disabled race in bh

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Date:   Wed, 9 Mar 2022 14:06:27 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        Chris Goldsworthy <cgoldswo@...eaurora.org>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        John Dias <joaodias@...gle.com>
Subject: Re: [PATCH] mm: fs: fix lru_cache_disabled race in bh_lru

On Tue,  8 Mar 2022 10:07:09 -0800 Minchan Kim <minchan@...nel.org> wrote:

> Check lru_cache_disabled under bh_lru_lock. Otherwise, it could
> introduce race below and it fails to migrate pages containing
> buffer_head.
> 
>    CPU 0					CPU 1
> 
> bh_lru_install
>                                        lru_cache_disable
>   lru_cache_disabled = false
>                                        atomic_inc(&lru_disable_count);
> 				       invalidate_bh_lrus_cpu of CPU 0
> 				       bh_lru_lock
> 				       __invalidate_bh_lrus
> 				       bh_lru_unlock
>   bh_lru_lock
>   install the bh
>   bh_lru_unlock

What are the user-visible runtime effects of this bug?

Is a cc:stable needed?

Should there be a reported-by?

Thanks.