linux-kernel - Re: [PATCH] tracing/profile: Fix profile_disable vs module

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Message-ID: <4A923197.4040708@cn.fujitsu.com>
Date:	Mon, 24 Aug 2009 14:22:15 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload

Peter Zijlstra wrote:
> On Mon, 2009-08-24 at 12:19 +0800, Li Zefan wrote:
>> If the correspoding module is unloaded before ftrace_profile_disable()
>> is called, event->profile_disable() won't be called, which can
>> cause oops:
>>
>>   # insmod trace-events-sample.ko
>>   # perf record -f -a -e sample:foo_bar sleep 3 &
>>   # sleep 1
>>   # rmmod trace_events_sample
>>   # insmod trace-events-sample.ko
>>   OOPS!
>>
>> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> 
> 
> Hrmm, feel fragile, why don't we check if all a modules tracepoints are
> unused on unload?
> 

I don't think it's fragile. We are profiling via a module's
tracepoint, so we should pin the module, via module_get().
If event->profile_enable() has been calld, we should make
sure it's profile_disable() will be called.

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