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Subject: Re: [PATCH] mm: cleancache: fix corruption on missed inode
 invalidation
References: <20181112095734.17979-1-ptikhomirov@virtuozzo.com>
 <20181112113153.GC7175@quack2.suse.cz>
From: Andrey Ryabinin <aryabinin@virtuozzo.com>
Message-ID: <2abdb97e-0fed-0fb5-6941-e7afcc9e0209@virtuozzo.com>
Date: Mon, 12 Nov 2018 14:40:06 +0300
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Sender: owner-linux-mm@kvack.org
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To: Jan Kara <jack@suse.cz>, Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Vasily Averin <vvs@virtuozzo.com>, Konstantin Khorenko <khorenko@virtuozzo.com>, Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mgorman@techsingularity.net>, Matthew Wilcox <willy@infradead.org>, Andi Kleen <ak@linux.intel.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org



On 11/12/18 2:31 PM, Jan Kara wrote:
> 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@linux-foundation.org>
>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>> Cc: Mel Gorman <mgorman@techsingularity.net>
>> Cc: Jan Kara <jack@suse.cz>
>> Cc: Matthew Wilcox <willy@infradead.org>
>> Cc: Andi Kleen <ak@linux.intel.com>
>> Cc: linux-mm@kvack.org
>> Cc: linux-kernel@vger.kernel.org
>> Reviewed-by: Vasily Averin <vvs@virtuozzo.com>
>> Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
>> Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.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...
> 	  */

Or we can just call cleancache_invalidate_inode(mapping) on else branch,
so the code would be more self-explanatory, and also avoid
function call in no-cleancache setups, which should the most of setups.