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Date: Wed, 26 Aug 2009 15:10:44 +0800
From: Li Zefan <lizf@cn.fujitsu.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: Ingo Molnar <mingo@elte.hu>, Steven Rostedt <rostedt@goodmis.org>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       LKML <linux-kernel@vger.kernel.org>,
       Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload
References: <20090824092455.GA25267@elte.hu>	 <1251106058.7538.149.camel@twins> <4A937505.5000209@cn.fujitsu.com>	 <1251181266.7538.1016.camel@twins> <4A9385AA.508@cn.fujitsu.com>	 <1251182405.7538.1050.camel@twins> <20090825090558.GC14003@elte.hu>	 <1251191546.7538.1118.camel@twins> <20090825102215.GC26801@elte.hu>	 <1251196359.7538.1133.camel@twins>  <20090825103907.GB28287@elte.hu>	 <1251197235.7538.1142.camel@twins> <1251211963.7538.1164.camel@twins>	 <4A94D3A8.1090902@cn.fujitsu.com>  <1251269207.7538.1217.camel@twins> <1251270092.7538.1226.camel@twins>
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Peter Zijlstra wrote:
> On Wed, 2009-08-26 at 08:46 +0200, Peter Zijlstra wrote:
> 
>> Aahh, I see the bug, its only ftrace that knows about the module, not
>> tracepoints themselves, _that_ needs fixing.
> 
> You could possibly do something like:
> 
>  struct module *tp_mod = __module_address(&some_tp_symbol);
>  struct module *cb_mod = __module_text_address(func);
> 
>  if (tp_mod && tp_mod != cb_mod) {
> 	ret = try_get_module(tp_mod);
> 	if (ret)
> 		goto fail;
>  }
> 
> in register_trace_##name() or thereabout.
> 

Actually I tried it, but it didn't work. As I said, You can't find
any tp symbol when registering tp callback. The same example again:

	In module bar, we have register_trace_foo()
	In module foo, we have DEFINE_TRACE(foo) and trace_foo().

bar doesn't know any symbol of foo, so it can't bump foo's refcnt,

*Note: you can load module bar without loading module foo*