linux-kernel - Re: [PATCH] Module : call synchronize_sched() between module exit() and free.

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Message-ID: <20080730114035.GD27711@redhat.com>
Date:	Wed, 30 Jul 2008 07:40:35 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] Module : call synchronize_sched() between module exit() and free.

Hi -

On Tue, Jul 29, 2008 at 10:27:51PM -0400, Mathieu Desnoyers wrote:
> [...]
> Actually, it's not placing a marker/tracepoint in a module which causes
> a problem, this is a simple function call after all, and correctly dealt
> with by current module.c code.
> [...]

Just to spell it out, it is this scenario I'd like to see documented:

module-foo.c:
   foo() { ... trace_mark (foo, "..."); ... }

module-bar.c:
   setup() { ... marker_probe_register ("foo" , ..., &foo_handler ); }
   teardown() { ... marker_probe_unregister ("foo" , ..., &foo_handler ); }
   foo_handler() { }

1)  module-foo loads
2)  module-bar loads
3)  module-bar.c:setup()
4)  module-foo unloads

What happens here?  Certainly no more calls to foo_handler, but is
that all?  (Would it not be desirable for an active marker to cause
module-foo's refcount to increase, so as to prevent unloading at this
time?)

5)  module-bar.c:teardown()

Can this teardown code succeed fully even if module-foo is already
dead and gone?
  

- FChE
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