From owner-svn-src-head@FreeBSD.ORG  Tue Jul  9 09:01:45 2013
Return-Path: <owner-svn-src-head@FreeBSD.ORG>
Delivered-To: svn-src-head@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by hub.freebsd.org (Postfix) with ESMTP id 5DE42C8D;
 Tue,  9 Jul 2013 09:01:45 +0000 (UTC) (envelope-from avg@FreeBSD.org)
Received: from svn.freebsd.org (svn.freebsd.org
 [IPv6:2001:1900:2254:2068::e6a:0])
 by mx1.freebsd.org (Postfix) with ESMTP id 5082711D3;
 Tue,  9 Jul 2013 09:01:45 +0000 (UTC)
Received: from svn.freebsd.org ([127.0.1.70])
 by svn.freebsd.org (8.14.7/8.14.7) with ESMTP id r6991juI023942;
 Tue, 9 Jul 2013 09:01:45 GMT (envelope-from avg@svn.freebsd.org)
Received: (from avg@localhost)
 by svn.freebsd.org (8.14.7/8.14.5/Submit) id r6991j64023941;
 Tue, 9 Jul 2013 09:01:45 GMT (envelope-from avg@svn.freebsd.org)
Message-Id: <201307090901.r6991j64023941@svn.freebsd.org>
From: Andriy Gapon <avg@FreeBSD.org>
Date: Tue, 9 Jul 2013 09:01:45 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
Subject: svn commit: r253077 - head/sys/kern
X-SVN-Group: head
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
X-BeenThere: svn-src-head@freebsd.org
X-Mailman-Version: 2.1.14
Precedence: list
List-Id: SVN commit messages for the src tree for head/-current
 <svn-src-head.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/svn-src-head>,
 <mailto:svn-src-head-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-head>
List-Post: <mailto:svn-src-head@freebsd.org>
List-Help: <mailto:svn-src-head-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-head>,
 <mailto:svn-src-head-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 09 Jul 2013 09:01:45 -0000

Author: avg
Date: Tue Jul  9 09:01:44 2013
New Revision: 253077
URL: http://svnweb.freebsd.org/changeset/base/253077

Log:
  should_yield: protect from td_swvoltick being uninitialized or too stale
  
  The distance between ticks and td_swvoltick should be calculated as
  an unsigned number.  Previously we could end up comparing a negative
  number with hogticks in which case should_yield() would give incorrect
  answer.
  
  We should probably ensure that td_swvoltick is properly initialized.
  
  Sponsored by:	HybridCluster
  MFC after:	5 days

Modified:
  head/sys/kern/kern_synch.c

Modified: head/sys/kern/kern_synch.c
==============================================================================
--- head/sys/kern/kern_synch.c	Tue Jul  9 08:59:39 2013	(r253076)
+++ head/sys/kern/kern_synch.c	Tue Jul  9 09:01:44 2013	(r253077)
@@ -581,7 +581,7 @@ int
 should_yield(void)
 {
 
-	return (ticks - curthread->td_swvoltick >= hogticks);
+	return ((unsigned int)(ticks - curthread->td_swvoltick) >= hogticks);
 }
 
 void