linux-kernel - Re: [PATCH] mm, compaction: avoid uninitialized variable use

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Date:	Thu, 12 May 2016 14:00:18 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Michal Hocko <mhocko@...nel.org>, Arnd Bergmann <arnd@...db.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...hsingularity.net>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Taku Izumi <izumi.taku@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, compaction: avoid uninitialized variable use

On 05/12/2016 08:16 AM, Michal Hocko wrote:
> I think this would be slightly better than your proposal. Andrew, could
> you fold it into the original
> mm-compaction-simplify-__alloc_pages_direct_compact-feedback-interface.patch
> patch?
> ---
>  From 434bc8b6f3787724327499998c4fe651e8ce5d68 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@...e.com>
> Date: Thu, 12 May 2016 08:10:33 +0200
> Subject: [PATCH] mmotm:
>   mm-compaction-simplify-__alloc_pages_direct_compact-feedback-interface-fix
>
> Arnd has reported the following compilation warning:
> mm/page_alloc.c: In function '__alloc_pages_nodemask':
> mm/page_alloc.c:3651:6: error: 'compact_result' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>
> This should be a false positive TRANSPARENT_HUGEPAGE depends on COMPACTION
> so is_thp_gfp_mask shouldn't be true. GFP_TRANSHUGE is a bit tricky
> and somebody might be using this accidently. Make sure that compact_result
> is defined also for !CONFIG_COMPACT and set it to COMPACT_SKIPPED because
> the compaction was really withdrawn.
>
> Reported-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Michal Hocko <mhocko@...e.com>

Ack.

> ---
>   mm/page_alloc.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4950d01ff935..0d9008042efa 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3300,6 +3300,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
>   		unsigned int alloc_flags, const struct alloc_context *ac,
>   		enum migrate_mode mode, enum compact_result *compact_result)
>   {
> +	*compact_result = COMPACT_SKIPPED;
>   	return NULL;
>   }
>
>