linux-kernel - Re: module-placed markers/tracepoints

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Message-Id: <200807301140.59745.rusty@rustcorp.com.au>
Date:	Wed, 30 Jul 2008 11:40:59 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	"Frank Ch. Eigler" <fche@...hat.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: module-placed markers/tracepoints

On Wednesday 30 July 2008 08:41:16 Mathieu Desnoyers wrote:
> Therefore, what would be needed here is to add a synchronize_sched()
> after mod->exit() in module.c or after each tracepoint/marker unregister
> in marker.c/tracepoint.c. However, I'd really prefer to add this to
> module.c since adding this for _every_ unregister will slow down
> processing or multiple probe unregistration too much.
>
> Rusty, am I understanding that correctly ?
>
> Mathieu

Hi Mathieu,

   Yes: stop_machine is merely used to atomically check the module refcount 
for zero and set the state so it can't be incremented again (ie. 
try_module_get will fail).

   So placing a tracepoint or marker in a module does not bump the module 
refcount?  If that's true, then there needs to be some kind of 
remove_markers_from_module() call after module->exit(), which should do the 
synchronize_sched() or whatever, right?

Rusty.
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