netdev - Re: [PATCH net v2] bonding: fix bond_poll_controller bh

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Message-Id: <20150828.141351.2056521281131696426.davem@davemloft.net>
Date:	Fri, 28 Aug 2015 14:13:51 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	razor@...ckwall.org
Cc:	netdev@...r.kernel.org, 13806511171@....com,
	shemminger@...ux-foundation.org, maheshb@...gle.com,
	j.vosburgh@...il.com, vfalico@...il.com, gospo@...ulusnetworks.com,
	nikolay@...ulusnetworks.com
Subject: Re: [PATCH net v2] bonding: fix bond_poll_controller bh_enable
 warning

From: Nikolay Aleksandrov <razor@...ckwall.org>
Date: Fri, 28 Aug 2015 10:22:20 -0700

> The problem is rcu_read_unlock_bh() which triggers a warning when
> irqs are disabled.  ndo_poll_controller can run with bh enabled,
> disabled or irqs disabled so check if that is the case and acquire
> rcu_read_lock_bh only when not running with disabled irqs.

I would say that having hard irqs disabled is a strict requirement, as
per the debugging test in netpoll_send_skb_on_dev():

	WARN_ON_ONCE(!irqs_disabled());

If you want to add the same check to netpoll_send_udp(), that's fine.

But what isn't fine is adding all of this conditional locking, we want
->poll_controller() implementations to be able to depend upon the IRQ
environment they execute in, otherwise every single implementation
might need to have ugly conditional locking as well.
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