linux-kernel - Re: [RFC PATCH][3.0] Tracepoint: dissociate from module mutex (v2)

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Date:	Wed, 10 Aug 2011 23:23:27 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>, tglx@...utronix.de,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [RFC PATCH][3.0] Tracepoint: dissociate from module mutex (v2)

On Thu, 2011-08-11 at 12:14 +0900, Masami Hiramatsu wrote:
> (2011/08/11 4:18), Mathieu Desnoyers wrote:
> > Copy the information needed from struct module into a local module list
> > held within tracepoint.c from within the module coming/going notifier.
> > 
> > This vastly simplifies locking of tracepoint registration /
> > unregistration, because we don't have to take the module mutex to
> > register and unregister tracepoints anymore. Steven Rostedt ran into
> > dependency problems related to modules mutex vs kprobes mutex vs ftrace
> > mutex vs tracepoint mutex that seems to be hard to fix without removing
> > this dependency between tracepoint and module mutex. (note: it should be
> > investigated whether kprobes could benefit of being dissociated from the
> > modules mutex too.)
> 
> Thanks, it seems that kprobes has already mostly done that.
> It holds module_mutex only in kprobe_optimizer. However,
> it seems meaningless, because kprobe_mutex already protects
> kprobe_optimizer against the kprobes module notifier.
> Thus, a module removing will stays on the notifier until
> the optimizer runs out. So I think we can remove that mutex lock.
> 

So should I change my patch 4/5 to just remove the module_mutex?

[PATCH 4/5][RFC] kprobes: Inverse taking of module_mutex with kprobe_mutex

-- Steve


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