From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Thu, 17 Aug 2006 01:48:01 -0700 (PDT) Received: from nf-out-0910.google.com (nf-out-0910.google.com [64.233.182.189]) by oss.sgi.com (8.12.10/8.12.10/SuSE Linux 0.7) with ESMTP id k7H8lcDW030841 for ; Thu, 17 Aug 2006 01:47:39 -0700 Received: by nf-out-0910.google.com with SMTP id a25so1008931nfc for ; Thu, 17 Aug 2006 01:47:07 -0700 (PDT) Message-ID: <9a8748490608170147o7bc9a457ud3e0a6729444c27e@mail.gmail.com> Date: Thu, 17 Aug 2006 10:47:07 +0200 From: "Jesper Juhl" Subject: Re: 'fbno' possibly used uninitialized in xfs_alloc_ag_vextent_small() In-Reply-To: <20060817084111.A2787212@wobbly.melbourne.sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <200608162327.34420.jesper.juhl@gmail.com> <20060817084111.A2787212@wobbly.melbourne.sgi.com> Sender: xfs-bounce@oss.sgi.com Errors-To: xfs-bounce@oss.sgi.com List-Id: xfs To: Nathan Scott Cc: linux-kernel@vger.kernel.org, xfs-masters@oss.sgi.com, xfs@oss.sgi.com On 17/08/06, Nathan Scott wrote: > Hi Jesper, > > On Wed, Aug 16, 2006 at 11:27:34PM +0200, Jesper Juhl wrote: > > (Please keep me on Cc since I'm not subscribed to the XFS lists) > > > > The coverity checker found what looks to me like a valid case of > > potentially uninitialized variable use (see below). > > It looks invalid, but its not, once again. To understand why this > isn't a problem requires looking at the xfs_alloc_ag_vextent_small > call sites (there's only two). If (*flen==0) is passed back out, > then the value in *fbno is discarded, always. > > > So basically, if we hit the 'else' branch, then 'fbno' has not been > > initialized and line 1490 will then use that uninitialized variable. > > > > What would prevent that from happening at some time?? > > Nothing. But its not a problem in practice. However, that final > else branch is very much unlikely, so theres no real cost to just > initialising the local fbno to NULLAGBLOCK in that branch, and we > future proof ourselves a bit that way I guess (in case the callers > ever change - pretty unlikely, but we may as well). How does the > patch below look to you? > Looks good to me. -- Jesper Juhl Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html Plain text mails only, please http://www.expita.com/nomime.html