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

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Date:	Wed, 26 Aug 2009 15:10:44 +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>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload

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*


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