netdev - Re: [PATCH net-next] neigh: Add missing rcu_assign

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Message-ID: <20150528135044.GA8313@gondor.apana.org.au>
Date:	Thu, 28 May 2015 21:50:44 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	ying.xue@...driver.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] neigh: Add missing rcu_assign_pointer

Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> This patch is not needed.
> 
> You really should read Documentation/RCU , because it looks like you are
> quite confused.
> 
> When we remove an element from a RCU protected list, all the objects in
> the chain are already ready to be caught by rcu readers.
> 
> Therefore, no additional memory barrier is needed before doing *np =
> n->next;
> 
> Please do not add spurious memory barriers. Like atomic operations, we
> want all of them being required and possibly documented.

This patch is indeed bogus but accessing an RCU-protected like
this will trigger sparse warnings.  So better make it an
RCU_INIT_POINTER.

Cheers,
-- 
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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