From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758391AbbA1VQl (ORCPT ); Wed, 28 Jan 2015 16:16:41 -0500 Received: from terminus.zytor.com ([198.137.202.10]:40980 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750894AbbA1Uuf (ORCPT ); Wed, 28 Jan 2015 15:50:35 -0500 Date: Wed, 28 Jan 2015 06:29:25 -0800 From: tip-bot for Jan Beulich Message-ID: Cc: torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, riel@redhat.com, hpa@zytor.com, JBeulich@suse.com, peterz@infradead.org, tglx@linutronix.de, jbeulich@suse.com, mingo@kernel.org Reply-To: hpa@zytor.com, riel@redhat.com, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, jbeulich@suse.com, mingo@kernel.org, peterz@infradead.org, JBeulich@suse.com, tglx@linutronix.de In-Reply-To: <54C2139202000078000588F7@mail.emea.novell.com> References: <54C2139202000078000588F7@mail.emea.novell.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/urgent] sched/fair: Avoid using uninitialized variable in preferred_group_nid() Git-Commit-ID: 81907478c4311a679849216abf723999184ab984 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 81907478c4311a679849216abf723999184ab984 Gitweb: http://git.kernel.org/tip/81907478c4311a679849216abf723999184ab984 Author: Jan Beulich AuthorDate: Fri, 23 Jan 2015 08:25:38 +0000 Committer: Ingo Molnar CommitDate: Wed, 28 Jan 2015 13:14:12 +0100 sched/fair: Avoid using uninitialized variable in preferred_group_nid() At least some gcc versions - validly afaict - warn about potentially using max_group uninitialized: There's no way the compiler can prove that the body of the conditional where it and max_faults get set/ updated gets executed; in fact, without knowing all the details of other scheduler code, I can't prove this either. Generally the necessary change would appear to be to clear max_group prior to entering the inner loop, and break out of the outer loop when it ends up being all clear after the inner one. This, however, seems inefficient, and afaict the same effect can be achieved by exiting the outer loop when max_faults is still zero after the inner loop. [ mingo: changed the solution to zero initialization: uninitialized_var() needs to die, as it's an actively dangerous construct: if in the future a known-proven-good piece of code is changed to have a true, buggy uninitialized variable, the compiler warning is then supressed... The better long term solution is to clean up the code flow, so that even simple minded compilers (and humans!) are able to read it without getting a headache. ] Signed-off-by: Jan Beulich Signed-off-by: Peter Zijlstra (Intel) Cc: Rik van Riel Cc: Linus Torvalds Link: http://lkml.kernel.org/r/54C2139202000078000588F7@mail.emea.novell.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 40667cb..fe331fc 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1730,7 +1730,7 @@ static int preferred_group_nid(struct task_struct *p, int nid) nodes = node_online_map; for (dist = sched_max_numa_distance; dist > LOCAL_DISTANCE; dist--) { unsigned long max_faults = 0; - nodemask_t max_group; + nodemask_t max_group = NODE_MASK_NONE; int a, b; /* Are there nodes at this distance from each other? */