linux-kernel - Re: [PATCH] mm: cleancache: fix potential race in cleancache apis

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Date:   Wed, 30 Jun 2021 10:13:28 +0200
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     권오훈 <ohoono.kwon@...sung.com>
Cc:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "ohkwon1043@...il.com" <ohkwon1043@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: cleancache: fix potential race in cleancache apis

On Wed, Jun 30, 2021 at 04:33:10PM +0900, 권오훈 wrote:
> Current cleancache api implementation has potential race as follows,
> which might lead to corruption in filesystems using cleancache.
> 
> thread 0                thread 1                        thread 2
> 
>                         in put_page
>                         get pool_id K for fs1
> invalidate_fs on fs1
> frees pool_id K
>                                                         init_fs for fs2
>                                                         allocates pool_id K
>                         put_page puts page
>                         which belongs to fs1
>                         into cleancache pool for fs2
> 
> At this point, a file cache which originally belongs to fs1 might be
> copied back to cleancache pool of fs2, which might be later used as if
> it were normal cleancache of fs2, and could eventually corrupt fs2 when
> flushed back.
> 
> Add rwlock in order to synchronize invalidate_fs with other cleancache
> operations.
> 
> In normal situations where filesystems are not frequently mounted or
> unmounted, there will be little performance impact since
> read_lock/read_unlock apis are used.
> 
> Signed-off-by: Ohhoon Kwon <ohoono.kwon@...sung.com>

What commit does this fix?  Should it go to stable kernels?

thanks,

greg k-h