linux-kernel - Re: [PATCH] mm: cleancache: fix corruption on missed inode invalidation

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Date:   Thu, 15 Nov 2018 14:31:03 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
Cc:     Vasily Averin <vvs@...tuozzo.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Konstantin Khorenko <khorenko@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Jan Kara <jack@...e.cz>, Matthew Wilcox <willy@...radead.org>,
        Andi Kleen <ak@...ux.intel.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: cleancache: fix corruption on missed inode
 invalidation

On Mon, 12 Nov 2018 12:57:34 +0300 Pavel Tikhomirov <ptikhomirov@...tuozzo.com> wrote:

> If all pages are deleted from the mapping by memory reclaim and also
> moved to the cleancache:
> 
> __delete_from_page_cache
>   (no shadow case)
>   unaccount_page_cache_page
>     cleancache_put_page
>   page_cache_delete
>     mapping->nrpages -= nr
>     (nrpages becomes 0)
> 
> We don't clean the cleancache for an inode after final file truncation
> (removal).
> 
> truncate_inode_pages_final
>   check (nrpages || nrexceptional) is false
>     no truncate_inode_pages
>       no cleancache_invalidate_inode(mapping)
> 
> These way when reading the new file created with same inode we may get
> these trash leftover pages from cleancache and see wrong data instead of
> the contents of the new file.
> 
> Fix it by always doing truncate_inode_pages which is already ready for
> nrpages == 0 && nrexceptional == 0 case and just invalidates inode.
> 

Data corruption sounds serious.  Shouldn't we backport this into
-stable kernels?