From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752089Ab1AEL7Z (ORCPT ); Wed, 5 Jan 2011 06:59:25 -0500 Received: from charlotte.tuxdriver.com ([70.61.120.58]:38693 "EHLO smtp.tuxdriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752014Ab1AEL7X (ORCPT ); Wed, 5 Jan 2011 06:59:23 -0500 Date: Wed, 5 Jan 2011 06:59:08 -0500 From: Neil Horman To: Mathieu Desnoyers Cc: Frederic Weisbecker , Zhaolei , LKML , Steven Rostedt , Ingo Molnar , Thomas Gleixner Subject: Re: [RFC patch 2/5] trace event skb fix unassigned field Message-ID: <20110105115908.GA4434@hmsreliant.think-freely.org> References: <20110104235418.GD2911@nowhere> <20110105004038.GB9737@Krystal> <20110105004903.GF2911@nowhere> <20110105012123.GA10416@Krystal> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110105012123.GA10416@Krystal> User-Agent: Mutt/1.5.21 (2010-09-15) X-Spam-Score: -1.1 (-) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 04, 2011 at 08:21:23PM -0500, Mathieu Desnoyers wrote: > * 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; > ), > > > Acked-by: Neil Horman > -- > Mathieu Desnoyers > Operating System Efficiency R&D Consultant > EfficiOS Inc. > http://www.efficios.com >