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

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Date:   Mon, 12 Nov 2018 12:31:53 +0100
From:   Jan Kara <jack@...e.cz>
To:     Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        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 12-11-18 12:57:34, Pavel Tikhomirov 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.
> 
> Fixes: commit 91b0abe36a7b ("mm + fs: store shadow entries in page cache")
> To: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Mel Gorman <mgorman@...hsingularity.net>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Andi Kleen <ak@...ux.intel.com>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Reviewed-by: Vasily Averin <vvs@...tuozzo.com>
> Reviewed-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Signed-off-by: Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
> ---
>  mm/truncate.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

The patch looks good but can you add a short comment before the
truncate_inode_pages() call explaining why it needs to be called always?
Something like:

	 /*
	  * Cleancache needs notification even if there are no pages or
	  * shadow entries...
	  */

Otherwise you can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> 
> diff --git a/mm/truncate.c b/mm/truncate.c
> index 45d68e90b703..4c56c19e76eb 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -517,9 +517,9 @@ void truncate_inode_pages_final(struct address_space *mapping)
>  		 */
>  		xa_lock_irq(&mapping->i_pages);
>  		xa_unlock_irq(&mapping->i_pages);
> -
> -		truncate_inode_pages(mapping, 0);
>  	}
> +
> +	truncate_inode_pages(mapping, 0);
>  }
>  EXPORT_SYMBOL(truncate_inode_pages_final);
>  
> -- 
> 2.17.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR