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Date: Tue, 4 Jan 2011 20:21:23 -0500 From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com> To: Frederic Weisbecker <fweisbec@...il.com> Cc: Zhaolei <zhaolei@...fujitsu.com>, "nhorman@...driver.com" <nhorman@...driver.com>, LKML <linux-kernel@...r.kernel.org>, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [RFC patch 2/5] trace event skb fix unassigned field * Frederic Weisbecker (fweisbec@...il.com) wrote: > On Tue, Jan 04, 2011 at 07:40:38PM -0500, Mathieu Desnoyers wrote: > > * Frederic Weisbecker (fweisbec@...il.com) wrote: > > > On Tue, Jan 04, 2011 at 06:46:06PM -0500, nhorman@...driver.com wrote: > > > > Acked- by: Neil Horman <nhorman@...driver.com> > > > > > > > > > > > > Sent from my Verizon Wireless Phone > > > > > > > > ----- Reply message ----- > > > > From: "Mathieu Desnoyers" <mathieu.desnoyers@...icios.com> > > > > Date: Tue, Jan 4, 2011 6:16 pm > > > > Subject: [RFC patch 2/5] trace event skb fix unassigned field > > > > To: "LKML" <linux-kernel@...r.kernel.org> > > > > Cc: "Mathieu Desnoyers" <mathieu.desnoyers@...icios.com>, "Steven Rostedt" <rostedt@...dmis.org>, "Frederic Weisbecker" <fweisbec@...il.com>, "Ingo Molnar" <mingo@...e.hu>, "Neil Horman" <nhorman@...driver.com>, "Thomas Gleixner" <tglx@...utronix.de> > > > > > > > > > > > > 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 <mathieu.desnoyers@...icios.com> CC: Steven Rostedt <rostedt@...dmis.org> CC: Frederic Weisbecker <fweisbec@...il.com> CC: Ingo Molnar <mingo@...e.hu> CC: Thomas Gleixner <tglx@...utronix.de> CC: Neil Horman <nhorman@...driver.com> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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