netdev - Re: Races in net_rx_action vs netpoll?

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Date:	Wed, 11 Jul 2007 19:33:20 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	okir@....de
Cc:	netdev@...r.kernel.org
Subject: Re: Races in net_rx_action vs netpoll?

From: Olaf Kirch <okir@....de>
Date: Wed, 11 Jul 2007 09:41:37 +0200

> On Wednesday 11 July 2007 07:44, David Miller wrote:
> > > +#ifdef CONFIG_NETPOLL
> > > +	/* Prevent race with netpoll - yes, this is a kludge.
> > > +	 * But at least it doesn't penalize the non-netpoll
> > > +	 * code path. */
> > > +	if (test_bit(__LINK_STATE_POLL_LIST_FROZEN, &dev->state))
> > > +		return;
> > > +#endif
> > > +
> > >  	local_irq_save(flags);
> > >  	BUG_ON(!test_bit(__LINK_STATE_RX_SCHED, &dev->state));
> > >  	list_del(&dev->poll_list);
> > 
> > That new bit can be set in interrupt context can't it?
> 
> It's set and cleared in poll_napi only, and as far as I can tell 
> poll_napi will only ever be called from via softirq, but never
> from an interrupt handler directly.
> 
> I also don't think the test_bit() needs to lock out interrupts.
> The only reason we do it for the RX_SCHED bit is that the RX_SCHED
> bit and the poll_list change must happen atomically wrt interrupts
> from the NIC, right?

Ok, sounds good.

I'll add merge your patch with a target of 2.6.23

If you really want, after this patch has sat in 2.6.23 for a while
and got some good testing, we can consider a submission for -stable.
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