linux-kernel - Re: [PATCH v4 4/6] hw_random: fix unregister race.

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Message-ID: <20141112044725.GA24812@gondor.apana.org.au>
Date:	Wed, 12 Nov 2014 12:47:25 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Amos Kong <akong@...hat.com>
Cc:	virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
	rusty@...tcorp.com.au, m@...s.ch, mpm@...enic.com,
	amit.shah@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/6] hw_random: fix unregister race.

On Mon, Nov 10, 2014 at 09:47:27PM +0800, Herbert Xu wrote:
> On Mon, Nov 03, 2014 at 11:56:24PM +0800, Amos Kong wrote:
> >
> > @@ -98,6 +99,8 @@ static inline void cleanup_rng(struct kref *kref)
> >  
> >  	if (rng->cleanup)
> >  		rng->cleanup(rng);
> 
> You need a compiler barrier here to prevent reordering.

Michael Büsch pointed out that we should actually have a memory
barrier here.  I thought we didn't need it because I was only
worried about the code in my original complaint.  However, expecting
driver writers to use correct synchronisation primitives is surely
asking too much.

So let's add an smp_wmb() here to ensure all side-effects of
cleanup is visible.

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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