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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 12:32:16 -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> <4AAA76B1.3020208@redhat.com>
Masami Hiramatsu wrote:
> 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.
Aah, NO. the caller of trace_remove_event_call() should have
trace_event_mutex before calling!
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division
e-mail: mhiramat@redhat.com