From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-iw0-f175.google.com ([209.85.223.175]:53343 "EHLO mail-iw0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934148AbZIDVWA convert rfc822-to-8bit (ORCPT ); Fri, 4 Sep 2009 17:22:00 -0400 MIME-Version: 1.0 In-Reply-To: <1252052757.26413.9.camel@pc1117.cambridge.arm.com> References: <1251958266-10692-1-git-send-email-lrodriguez@atheros.com> <1251962791.3336.3.camel@johannes.local> <43e72e890909031113r6010519br3b81d15cc331ba85@mail.gmail.com> <1252001837.9336.2.camel@johannes.local> <20090903204319.GC3701@mosca> <1252040671.9336.10.camel@johannes.local> <1252052757.26413.9.camel@pc1117.cambridge.arm.com> From: "Luis R. Rodriguez" Date: Fri, 4 Sep 2009 14:21:40 -0700 Message-ID: <43e72e890909041421m243bbea6i95c26ab21dc8732d@mail.gmail.com> Subject: Re: [PATCH] cfg80211: clear cfg80211_inform_bss() from kmemleak reports To: Catalin Marinas , "John W. Linville" Cc: Johannes Berg , Luis Rodriguez , "linux-kernel@vger.kernel.org" , "linux-wireless@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Fri, Sep 4, 2009 at 1:25 AM, Catalin Marinas wrote: > On Fri, 2009-09-04 at 07:04 +0200, Johannes Berg wrote: >> On Thu, 2009-09-03 at 13:43 -0700, Luis R. Rodriguez wrote: >> > On Thu, Sep 03, 2009 at 11:17:17AM -0700, Johannes Berg wrote: >> > > On Thu, 2009-09-03 at 11:13 -0700, Luis R. Rodriguez wrote: >> > > >> > > > What I meant is it gobbles it up and spits another thing out. When it >> > > > gobbles it up the routine then uses kref_put(). >> > > > >> > > > > Why can it not track this? >> > > > >> > > > It probably can, just not sure if it follows kref_put(), I was under >> > > > the impression here it doesn't and because of it we were getting false >> > > > positives. Catalin, can you confirm? >> > > >> > > Ah I'd think that if it can't track it then that's because we use a >> > > pointer to the middle of the struct to keep track of it much of the >> > > time. >> > >> > So you agree with the patch but not the commit log entry? >> >> I'm not sure -- I think kmemleak should be able to figure it out, and if >> you were using IBSS then we actually have a leak that we need to plug, >> but otherwise I'd prefer to get some more input from Catalin first. > > First of all, kmemleak_ignore() is not the right function to mark a > false positive as it completely ignores an object even though it may > have pointers to others. The kmemleak_not_leak() function should be > used. However, there are only two places in the kernel where this was > actually needed (one of them is a real leak but we ignore it as it makes > the code more complicated). > > So, I think we should try to figure out why kmemleak reports it. There > are a few common cases: >     1. transient false positive - this should disappear after a few >        scans >     2. a pointer leading to the reported object is stored in an area of >        memory not scanned by kmemleak - most commonly pages allocated >        explicitly (alloc_pages etc.) as kmemleak doesn't track these. >        The preferred solution is to inform kmemleak about such page >        (kmemleak_alloc/kmemleak_free) rather than marking the false >        positive >     3. a pointer leading to the reported object isn't actually pointing >        to anywhere inside the structure (i.e. using the physical >        address). Here we would use kmemleak_not_leak() John please revert this merged patch (b563f91105758c35d7cd4589992198b9da52d579) on wireless-testing as we'd like to investigate further why we get this. BTW I should not I got this kmemleak report after using the clear command by painting objects black. I'll test it now with your suggested changes. Luis