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

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Date:	Wed, 26 Aug 2009 17:21:15 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	Li Zefan <lizf@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/profile: Fix profile_disable vs module_unload


On Wed, 26 Aug 2009, Mathieu Desnoyers wrote:
> * Steven Rostedt (rostedt@...dmis.org) wrote:

> > Anyway, this prevents your tracepoints from doing the odd things of 
> > loading a probe before it exists. Well you can, but then you prevent the 
> > unload of the module that registered it. Fine, I chucked out that patch.
> > 
> 
> you should try adding the required tracepoint_synchronize_unregister()
> call to ftrace_profile_disable_##call in ftrace.h. I expect this will
> fix your problem.

Just did, and it did not solve the bug.

> 
> Note that this is a bit slow to call it at each unregistration. Ideally,
> a module containing tracepoint probes should call this synchronization
> primitive only once at module unload.

The bug looks like it is registering a probe, but not unregistering it 
before leaving the module. But when the module is loaded again, it now has 
a bad function to call when the tracepoint is hit.

-- Steve
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