linux-kernel - Re: Is module refcounting racy?

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Message-ID: <alpine.LFD.2.00.1004010852170.3707@i5.linux-foundation.org>
Date:	Thu, 1 Apr 2010 08:55:59 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Nick Piggin <npiggin@...e.de>
cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Nick Piggin <npiggin@...il.com>, linux-kernel@...r.kernel.org,
	Jon Masters <jonathan@...masters.org>
Subject: Re: Is module refcounting racy?

On Thu, 1 Apr 2010, Nick Piggin wrote:
> 
> I think it can be done racelessly with my patch, which is not really too
> much overhead. I think if this is considered too much, then we should
> either fix code and preferably de-export and remove module_refcount from
> drivers, or remove module removal completely.

I doubt your patch matters too much, but I like it conceptually and it 
seems to be a nice basis for perhaps doing something clever in the long 
run.

[ ie avoiding the stop_machine and instead perhaps doing some optimistic 
  thing like "see if we seem to be unused right now, then unregister us, 
  and see - after unregistering - that the usage counts haven't increased, 
  and re-register if they have. ]

So I'd like to apply it as a "good improvement, even if module unloading 
which is the only thing that _should_ care deeply should already be under 
stop-machine".

But I'd like an ack or two first.

		Linus
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