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

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Message-Id: <69380EC5-CF63-48BE-AFCB-4F70E6869DFC@cumulusnetworks.com>
Date:	Fri, 28 Aug 2015 14:59:40 -0700
From:	Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, 13806511171@....com,
	shemminger@...ux-foundation.org, maheshb@...gle.com,
	j.vosburgh@...il.com, vfalico@...il.com, gospo@...ulusnetworks.com
Subject: Re: [PATCH net v2] bonding: fix bond_poll_controller bh_enable warning


> On Aug 28, 2015, at 2:13 PM, David Miller <davem@...emloft.net> wrote:
> 
> 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.

Great, that is what I wanted to know because I got confused by some older
commits. This will simplify the fix and I will add the warn_on in netpoll_send_udp().
v3 coming up

Thank you,
 Nik--
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