Messages in this thread Patch in this message | | | Date | Tue, 4 Jan 2011 19:40:38 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [RFC patch 2/5] trace event skb fix unassigned field |
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* Frederic Weisbecker (fweisbec@gmail.com) wrote: > On Tue, Jan 04, 2011 at 06:46:06PM -0500, nhorman@tuxdriver.com wrote: > > Acked- by: Neil Horman <nhorman@tuxdriver.com> > > > > > > Sent from my Verizon Wireless Phone > > > > ----- Reply message ----- > > From: "Mathieu Desnoyers" <mathieu.desnoyers@efficios.com> > > Date: Tue, Jan 4, 2011 6:16 pm > > Subject: [RFC patch 2/5] trace event skb fix unassigned field > > To: "LKML" <linux-kernel@vger.kernel.org> > > Cc: "Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>, "Steven Rostedt" <rostedt@goodmis.org>, "Frederic Weisbecker" <fweisbec@gmail.com>, "Ingo Molnar" <mingo@elte.hu>, "Neil Horman" <nhorman@tuxdriver.com>, "Thomas Gleixner" <tglx@linutronix.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 ?
Mathieu
> > > > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > > CC: Steven Rostedt <rostedt@goodmis.org> > > CC: Frederic Weisbecker <fweisbec@gmail.com> > > CC: Ingo Molnar <mingo@elte.hu> > > CC: Neil Horman <nhorman@tuxdriver.com> > > CC: Thomas Gleixner <tglx@linutronix.de> > > --- > > 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 = skb ? ntohs(skb->protocol) : 0; > > __entry->location = location; > > ), > > > > > >
-- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com
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