From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753313Ab0LTGLY (ORCPT ); Mon, 20 Dec 2010 01:11:24 -0500 Received: from mail-wy0-f174.google.com ([74.125.82.174]:57450 "EHLO mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750783Ab0LTGLX (ORCPT ); Mon, 20 Dec 2010 01:11:23 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:mail-followup-to:mime-version :content-type:content-disposition:user-agent; b=e+BND+0iFVyQ/YcyUNo0M0ymNmIBZpJQVkJ/IdW9Ri6P1XCjQwHmHLikLP2stFcvuu iBQ5zm3zZZJMBUrFLpI9tq9pW93CfKuWYPmntTNdj5sA6SiXFFfK4i1DmKmGCRTeUUxg 0Uz4URFhbaBFNwuYiFIPCMW/ys85wCJ4Xsx4I= Date: Mon, 20 Dec 2010 09:10:41 +0300 From: Dan Carpenter To: Paul Turner Cc: Peter Zijlstra , linux-kernel@vger.kernel.org Subject: [smatch] sched_fair: check after dereference Message-ID: <20101220061041.GA8512@bicker> Mail-Followup-To: Dan Carpenter , Paul Turner , Peter Zijlstra , linux-kernel@vger.kernel.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Paul, In linux-next e33078baa4 "sched: Fix update_cfs_load() synchronization" introduced a dereference before the check for NULL. I don't know the code well enough to say if it's a bug or if the check can be removed. kernel/sched_fair.c +728 update_cfs_load(6) warn: variable dereferenced before check 'cfs_rq' 722 static void update_cfs_load(struct cfs_rq *cfs_rq, int global_update) 723 { 724 u64 period = sysctl_sched_shares_window; 725 u64 now, delta; 726 unsigned long load = cfs_rq->load.weight; ^^^^^^^^^^^^^^^^^^^ 727 728 if (!cfs_rq) ^^^^^^ 729 return; Can you take a look? regards, dan carpenter