From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751259Ab1AEBV1 (ORCPT ); Tue, 4 Jan 2011 20:21:27 -0500 Received: from mail.openrapids.net ([64.15.138.104]:49347 "EHLO blackscsi.openrapids.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750801Ab1AEBV0 (ORCPT ); Tue, 4 Jan 2011 20:21:26 -0500 Date: Tue, 4 Jan 2011 20:21:23 -0500 From: Mathieu Desnoyers To: Frederic Weisbecker Cc: Zhaolei , "nhorman@tuxdriver.com" , LKML , Steven Rostedt , Ingo Molnar , Thomas Gleixner Subject: Re: [RFC patch 2/5] trace event skb fix unassigned field Message-ID: <20110105012123.GA10416@Krystal> References: <20110104235418.GD2911@nowhere> <20110105004038.GB9737@Krystal> <20110105004903.GF2911@nowhere> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110105004903.GF2911@nowhere> X-Editor: vi X-Info: http://www.efficios.com X-Operating-System: Linux/2.6.26-2-686 (i686) X-Uptime: 20:17:24 up 42 days, 6:20, 5 users, load average: 0.18, 0.06, 0.02 User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Frederic Weisbecker (fweisbec@gmail.com) wrote: > On Tue, Jan 04, 2011 at 07:40:38PM -0500, Mathieu Desnoyers wrote: > > * Frederic Weisbecker (fweisbec@gmail.com) wrote: > > > On Tue, Jan 04, 2011 at 06:46:06PM -0500, nhorman@tuxdriver.com wrote: > > > > Acked- by: Neil Horman > > > > > > > > > > > > Sent from my Verizon Wireless Phone > > > > > > > > ----- Reply message ----- > > > > From: "Mathieu Desnoyers" > > > > Date: Tue, Jan 4, 2011 6:16 pm > > > > Subject: [RFC patch 2/5] trace event skb fix unassigned field > > > > To: "LKML" > > > > Cc: "Mathieu Desnoyers" , "Steven Rostedt" , "Frederic Weisbecker" , "Ingo Molnar" , "Neil Horman" , "Thomas Gleixner" > > > > > > > > > > > > The field "protocol" in event kfree_skb is left unassigned if skb is NULL, > > > > leaving its trace output as garbage. Assign the value to 0 when skb is NULL > > > > instead. > > > > > > Hm, if the skb is already null, we probably shouldn't send any trace. > > > > > > What about using TP_CONDITION() ? > > > > Hrm, let's see. It's been introduced by commit > > 5cb3d1d9d34ac04bcaa2034139345b2a5fea54c1 > > by Zhaolei. > > > > Event at the time of that commit, the only caller looked like: > > > > void kfree_skb(struct sk_buff *skb) > > { > > if (unlikely(!skb)) > > return; > > if (likely(atomic_read(&skb->users) == 1)) > > smp_rmb(); > > else if (likely(!atomic_dec_and_test(&skb->users))) > > return; > > trace_kfree_skb(skb, __builtin_return_address(0)); > > __kfree_skb(skb); > > } > > EXPORT_SYMBOL(kfree_skb); > > > > So it already checks for a null pointer before calling the tracepoint. This > > leads me to wonder why why this check was added in the first place ? > > Likely for no strong reasons :) > > So I guess we can remove the check from the tracepoint? Yep, leading to this patch instead: trace event skb remove duplicate null-pointer check The check for NULL skb in the kfree_skb trace event is a duplicate from the check already done in its only caller, kfree_skb(). Remove this duplicate check. Signed-off-by: Mathieu Desnoyers CC: Steven Rostedt CC: Frederic Weisbecker CC: Ingo Molnar CC: Thomas Gleixner CC: Neil Horman --- include/trace/events/skb.h | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) Index: linux-2.6-lttng/include/trace/events/skb.h =================================================================== --- linux-2.6-lttng.orig/include/trace/events/skb.h +++ linux-2.6-lttng/include/trace/events/skb.h @@ -25,9 +25,7 @@ TRACE_EVENT(kfree_skb, TP_fast_assign( __entry->skbaddr = skb; - if (skb) { - __entry->protocol = ntohs(skb->protocol); - } + __entry->protocol = ntohs(skb->protocol); __entry->location = location; ), -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com