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Date:   Wed, 9 Mar 2022 14:06:27 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Minchan Kim <minchan@kernel.org>
Cc:     linux-mm <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        Chris Goldsworthy <cgoldswo@codeaurora.org>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        John Dias <joaodias@google.com>
Subject: Re: [PATCH] mm: fs: fix lru_cache_disabled race in bh_lru
Message-Id: <20220309140627.eeaa069daa921dbef64f8970@linux-foundation.org>
In-Reply-To: <20220308180709.2017638-1-minchan@kernel.org>
References: <20220308180709.2017638-1-minchan@kernel.org>
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On Tue,  8 Mar 2022 10:07:09 -0800 Minchan Kim <minchan@kernel.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.