netdev - Re: [PATCH RFC] gianfar: Make polling safe with IRQs disabled

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Message-ID: <20091109133231.GA26965@oksana.dev.rtsoft.ru>
Date:	Mon, 9 Nov 2009 16:32:31 +0300
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	David Miller <davem@...emloft.net>
Cc:	afleming@...escale.com, jason.wessel@...driver.com,
	netdev@...r.kernel.org, linuxppc-dev@...abs.org
Subject: Re: [PATCH RFC] gianfar: Make polling safe with IRQs disabled

On Sun, Nov 08, 2009 at 01:05:33AM -0800, David Miller wrote:
...
> > When using KGDBoE, gianfar driver spits 'Interrupt problem' messages,
> > which appears to be a legitimate warning, i.e. we may end up calling
> > netif_receive_skb() or vlan_hwaccel_receive_skb() with IRQs disabled.
> > 
> > This patch reworks the RX path so that if netpoll is enabled (the
> > only case when the driver don't know from what context the polling
> > may be called), we check whether IRQs are disabled, and if so we
> > fall back to safe variants of skb receiving functions.
> 
> This is bogus, I'll tell you why.
> 
> When you go into netif_receive_skb() we have a special check,
> "if (netpoll_receive_skb(..." that takes care of all of the
> details concerning doing a ->poll() from IRQ disabled context
> via netpoll.
> 
> So this code you're adding should not be necessary.
> 
> Or, explain to me why no other driver needs special logic in their
> ->poll() handler like this and does not run into any kinds of netpoll
> problems :-)

Hm, I was confused by the following note:

/**
 *      netif_receive_skb - process receive buffer from network
 *      @skb: buffer to process
...
 *      This function may only be called from softirq context and interrupts
 *      should be enabled.


Looking into the code though, I can indeed see that there
are netpoll checks, and __netpoll_rx() is actually called with
irqs disabled. So, in the end it appears that we should just
remove the 'Interrupt problem' message.


Thanks!

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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