netdev - Re: [PATCH net-next v1 2/2] bonding: Simplify the xmit function for modes that use xmit

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Message-ID: <1410151290.11872.80.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Sun, 07 Sep 2014 21:41:30 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Mahesh Bandewar <maheshb@...gle.com>
Cc:	Nikolay Aleksandrov <nikolay@...hat.com>,
	Jay Vosburgh <j.vosburgh@...il.com>,
	Veaceslav Falico <vfalico@...hat.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Maciej Zenczykowski <maze@...gle.com>
Subject: Re: [PATCH net-next v1 2/2] bonding: Simplify the xmit function for
 modes that use xmit_hash

On Sun, 2014-09-07 at 19:23 -0700, Mahesh Bandewar wrote:
> >
> I'm not expecting any writer protection here since all the paths are
> covered with some or the other lock at this moment. Just though that
> performing array manipulation in RCU context would be useful.


It is not useful. It is confusing only.

If you think of RCU as a replacement for reader/writer lock, its obvious
that once you get the writer lock, there is no need to get the reader
lock.

Extract from Documentation/RCU/whatisRCU.txt :

Use rcu_read_lock() and rcu_read_unlock() to guard RCU
read-side critical sections.

Use some solid scheme (such as locks or semaphores) to
keep concurrent updates from interfering with each other.



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