linux-kernel - Re: [RFC, DEBUGGING 1/2] mm: pass NR_FILE_PAGES/NR_SHMEM into node_page

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Date:	Thu, 23 Jun 2016 11:41:24 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...riel.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC, DEBUGGING 1/2] mm: pass NR_FILE_PAGES/NR_SHMEM into
 node_page_state

On Thu, Jun 23, 2016 at 12:05:17PM +0200, Arnd Bergmann wrote:
> I see some new warnings from a recent mm change:
> 
> mm/filemap.c: In function '__delete_from_page_cache':
> include/linux/vmstat.h:116:2: error: array subscript is above array bounds [-Werror=array-bounds]
>   atomic_long_add(x, &zone->vm_stat[item]);
>   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> include/linux/vmstat.h:116:35: error: array subscript is above array bounds [-Werror=array-bounds]
>   atomic_long_add(x, &zone->vm_stat[item]);
>                       ~~~~~~~~~~~~~^~~~~~
> include/linux/vmstat.h:116:35: error: array subscript is above array bounds [-Werror=array-bounds]
> include/linux/vmstat.h:117:2: error: array subscript is above array bounds [-Werror=array-bounds]
> 
> Looking deeper into it, I find that we pass the wrong enum
> into some functions after the type for the symbol has changed.
> 
> This changes the code to use the other function for those that
> are using the incorrect type. I've done this blindly just going
> by warnings I got from a debug patch I did for this, so it's likely
> that some cases are more subtle and need another change, so please
> treat this as a bug-report rather than a patch for applying.
> 

I have an alternative fix for this in a private tree. For now, I've asked
Andrew to withdraw the series entirely as there are non-trivial collisions
with OOM detection rework and huge page support for tmpfs.  It'll be easier
and safer to resolve this outside of mmotm as it'll require a full round
of testing which takes 3-4 days.

Thanks.

-- 
Mel Gorman
SUSE Labs