From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id D96B46B0005 for ; Wed, 11 May 2016 10:58:23 -0400 (EDT) Received: by mail-wm0-f71.google.com with SMTP id w143so44526921wmw.3 for ; Wed, 11 May 2016 07:58:23 -0700 (PDT) Received: from mout.kundenserver.de (mout.kundenserver.de. [212.227.126.130]) by mx.google.com with ESMTPS id 71si39214187wmr.122.2016.05.11.07.58.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 11 May 2016 07:58:22 -0700 (PDT) From: Arnd Bergmann Subject: Re: [PATCH] mm, compaction: avoid uninitialized variable use Date: Wed, 11 May 2016 16:52:41 +0200 Message-ID: <2695751.e2s15gCWav@wuerfel> In-Reply-To: <20160511144407.GA21503@dhcp22.suse.cz> References: <1462973126-1183468-1-git-send-email-arnd@arndb.de> <20160511144407.GA21503@dhcp22.suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , Mel Gorman , Vlastimil Babka , David Rientjes , Joonsoo Kim , Taku Izumi , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Wednesday 11 May 2016 16:44:07 Michal Hocko wrote: > 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 Ok, sounds good. > --- > 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; > } > I thought about this but didn't know which COMPACT_* value was appropriate here. The behavior then changes a bit with your approach compared to mine, because if (compact_result == COMPACT_DEFERRED) goto nopage; is true now. I assume this is what we want though. Arnd -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org