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Re: [PATCH tracing/kprobes 5/7] tracing/kprobes: Add argument name support
- From: Masami Hiramatsu <mhiramat at redhat dot com>
- To: rostedt at goodmis dot org
- Cc: Frederic Weisbecker <fweisbec at gmail dot com>, Ingo Molnar <mingo at elte dot hu>, lkml <linux-kernel at vger dot kernel dot org>, systemtap <systemtap at sources dot redhat dot com>, DLE <dle-develop at lists dot sourceforge dot net>, Jim Keniston <jkenisto at us dot ibm dot com>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Andi Kleen <ak at linux dot intel dot com>, Christoph Hellwig <hch at infradead dot org>, "Frank Ch. Eigler" <fche at redhat dot com>, "H. Peter Anvin" <hpa at zytor dot com>, Jason Baron <jbaron at redhat dot com>, "K.Prasad" <prasad at linux dot vnet dot ibm dot com>, Lai Jiangshan <laijs at cn dot fujitsu dot com>, Li Zefan <lizf at cn dot fujitsu dot com>, Peter Zijlstra <peterz at infradead dot org>, Srikar Dronamraju <srikar at linux dot vnet dot ibm dot com>, Tom Zanussi <tzanussi at gmail dot com>
- Date: Fri, 11 Sep 2009 12:11:29 -0400
- Subject: Re: [PATCH tracing/kprobes 5/7] tracing/kprobes: Add argument name support
- References: <20090910235258.22412.29317.stgit@dhcp-100-2-132.bos.redhat.com> <20090910235337.22412.77383.stgit@dhcp-100-2-132.bos.redhat.com> <1252678079.18996.665.camel@gandalf.stny.rr.com>
Steven Rostedt wrote:
> On Thu, 2009-09-10 at 19:53 -0400, Masami Hiramatsu wrote:
>
>> @@ -870,9 +892,13 @@ print_kprobe_event(struct trace_iterator *iter, int flags)
>> {
>> struct kprobe_trace_entry *field;
>> struct trace_seq *s =&iter->seq;
>> + struct trace_event *event;
>> + struct trace_probe *tp;
>> int i;
>>
>> field = (struct kprobe_trace_entry *)iter->ent;
>> + event = ftrace_find_event(field->ent.type);
>> + tp = container_of(event, struct trace_probe, event);
>
> Can this function be called the data is in the ring buffer, but the
> probe has been unregistered? If so, the result of ftrace_find_event be
> NULL?
Hmm, it will depend on ftrace implementation. Before releasing
trace_probe, kprobe tracer tries to unregister event call.
If it's correctly locking mutex or some rw_lock for both of
unregistering and printing, it will be safe.
Unfortunately, it seems not :-(.
In trace_events.c,
1054 static void __trace_remove_event_call(struct ftrace_event_call *call)
1055 {
1056 ftrace_event_enable_disable(call, 0);
1057 if (call->event)
1058 __unregister_ftrace_event(call->event);
What we need to do is calling unregister_ftrace_event() instead of
__unregister_ftrace_event.
Thank you,
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division
e-mail: mhiramat@redhat.com