netdev - Re: [PATCH] igb: completely disable interrupts during netpoll

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Message-Id: <20080625.152751.154176346.davem@davemloft.net>
Date:	Wed, 25 Jun 2008 15:27:51 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	andy@...yhouse.net
Cc:	jeffrey.t.kirsher@...el.com, jesse.brandeburg@...el.com,
	bruce.w.allan@...el.com, john.ronciak@...el.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH] igb: completely disable interrupts during netpoll

From: Andy Gospodarek <andy@...yhouse.net>
Date: Wed, 25 Jun 2008 10:15:11 -0400

> 
> Globally disable the interrupt during netpoll rather than simply
> disabling it on the hardware.  This will ensure all pending operations
> are complete and no more will execute.  I've seen reports of deadlocks
> with the current driver and this patch resolves them.

I don't want to see network drivers start getting into the habit
of doing this.  This operation could be extremely expensive with
certain IRQ controllers.

It's better to have a good understanding of why the deadlocks
happen, and this was decidedly missing from your commit message.

NAPI is designed in such a way that if pending interrupts arrive
after NAPI disables chip interrupts it should be handled just
fine and in fact I see this happen all the time on some of my
test systems.
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