From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932282AbcEKOoM (ORCPT ); Wed, 11 May 2016 10:44:12 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:36794 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751647AbcEKOoL (ORCPT ); Wed, 11 May 2016 10:44:11 -0400 Date: Wed, 11 May 2016 16:44:07 +0200 From: Michal Hocko To: Arnd Bergmann Cc: Andrew Morton , Mel Gorman , Vlastimil Babka , David Rientjes , Joonsoo Kim , Taku Izumi , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm, compaction: avoid uninitialized variable use Message-ID: <20160511144407.GA21503@dhcp22.suse.cz> References: <1462973126-1183468-1-git-send-email-arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1462973126-1183468-1-git-send-email-arnd@arndb.de> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 11-05-16 15:24:44, Arnd Bergmann wrote: > A recent rework of the compaction code introduced a warning about > an uninitialized variable when CONFIG_COMPACTION is disabled and > __alloc_pages_direct_compact() does not set its 'compact_result' > output argument: > > 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 adds another check for CONFIG_COMPACTION to ensure we never > evaluate the uninitialized variable in this configuration, which > is probably the simplest way to avoid the warning. I think that hiding this into __alloc_pages_direct_compact is a better idea. See the diff below > > A more elaborate rework might make this more readable. > > Signed-off-by: Arnd Bergmann > Fixes: 13cff7b81275 ("mm, compaction: simplify __alloc_pages_direct_compact feedback interface") Please do not use SHA for mmotm commits because they are unstable and change each linux-next release. --- diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 4950d01ff935..14e3b4d93adc 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_DEFERRED; return NULL; } -- Michal Hocko SUSE Labs