netdev - Re: [PATCH 1/1] bond: relocate rcu_read_lock and rcu_read

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Message-ID: <56AF3B24.7000207@cumulusnetworks.com>
Date:	Mon, 1 Feb 2016 12:01:56 +0100
From:	Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:	zyjzyj2000@...il.com, j.vosburgh@...il.com, vfalico@...il.com,
	gospo@...ulusnetworks.com, netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] bond: relocate rcu_read_lock and rcu_read_unlock

On 02/01/2016 04:31 AM, zyjzyj2000@...il.com wrote:
> From: Zhu Yanjun <zyjzyj2000@...il.com>
> 
> rcu_read_lock and rcu_read_unlock are to protect the function
> bond_miimon_inspect. As such, moving rcu_read_lock and rcu_read_unlock
> to the function bond_miimon_inspect to make the source code compact.
> 
> CC: Jay Vosburgh <j.vosburgh@...il.com>
> CC: Veaceslav Falico <vfalico@...il.com>
> CC: Andy Gospodarek <gospo@...ulusnetworks.com>
> Signed-off-by: Zhu Yanjun <zyjzyj2000@...il.com>
> ---
>  drivers/net/bonding/bond_main.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 

Not true, RCU also protects the slave dereference in bond_should_notify_peers().
Even though there's already a rcu_read_lock() while doing the dereference
itself, it is there only to please RCU, IIRC. The only "simplification" you
can do is remove the rcu_read_lock/unlock() around the slave deref in
bond_should_notify_peers and use rcu_dereference_rtnl() as it can be used either
in RCU protected region or with RTNL held. Also I think net-next is still
closed (and that's where this should be targeted at).

Cheers,
 Nik