Subject: Re: [PATCH 1/1] bond: relocate rcu_read_lock and rcu_read_unlock

From: Nikolay Aleksandrov <[email-masked]>
Date: Mon, 1 Feb 2016 12:01:56 +0100

On 02/01/2016 04:31 AM, [email-masked] wrote:
> From: Zhu Yanjun <[email-masked]>
> 
> 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 <[email-masked]>
> CC: Veaceslav Falico <[email-masked]>
> CC: Andy Gospodarek <[email-masked]>
> Signed-off-by: Zhu Yanjun <[email-masked]>
> ---
>  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