netdev - Re: [PATCH] Fix inet_diag.ko register vs rcv race

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Message-ID: <20071129124717.GD12069@ghostprotocols.net>
Date:	Thu, 29 Nov 2007 10:47:17 -0200
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Pavel Emelyanov <xemul@...nvz.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Linux Netdev List <netdev@...r.kernel.org>, devel@...nvz.org
Subject: Re: [PATCH] Fix inet_diag.ko register vs rcv race

Em Thu, Nov 29, 2007 at 11:37:34PM +1100, Herbert Xu escreveu:
> On Tue, Nov 27, 2007 at 04:09:43PM +0300, Pavel Emelyanov wrote:
> > The following race is possible when one cpu unregisters the handler
> > while other one is trying to receive a message and call this one:
> 
> Good catch! But I think we need a bit more to close this fully.
> 
> Dumps can resume asynchronously which means that they won't be
> holding inet_diag_mutex.  We can fix that pretty easily by
> giving that as our cb_mutex.
> 
> So could you add that to your patch and resubmit?
> 
> Arnaldo, synchronize_rcu() doesn't work on its own.  Whoever accesses
> the object that it's supposed to protect has to use the correct RCU
> primitives for this to work.
> 
> Synchronisation is like tango, it always takes two to make it work :)

Agreed, I didn't checked that when refactoring inet_diag, leaving this
as it was before I put my hands on it :-)

- Arnaldo
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