netdev - Re: [PATCH net-next 1/6] rtnetlink: use rcu_dereference

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Message-ID: <20170810153815.GA22889@splinter>
Date:   Thu, 10 Aug 2017 18:38:15 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     Florian Westphal <fw@...len.de>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net-next 1/6] rtnetlink: use rcu_dereference_raw to
 silence rcu splat

On Thu, Aug 10, 2017 at 04:52:57PM +0200, Florian Westphal wrote:
> Ido reports a rcu splat in __rtnl_register.
> The splat is correct; as rtnl_register doesn't grab any logs
> and doesn't use rcu locks either.  It has always been like this.
> handler families are not registered in parallel so there are no
> races wrt. the kmalloc ordering.
> 
> The only reason to use rcu_dereference in the first place was to
> avoid sparse from complaining about this.
> 
> Thus this switches to _raw() to not have rcu checks here.
> 
> The alternative is to add rtnl locking to register/unregister,
> however, I don't see a compelling reason to do so as this has been
> lockless for the past twenty years or so.
> 
> Fixes: 6853dd4881 ("rtnetlink: protect handler table with rcu")
> Reported-by: Ido Schimmel <idosch@...sch.org>
> Signed-off-by: Florian Westphal <fw@...len.de>

Tested-by: Ido Schimmel <idosch@...lanox.com>

Thanks!