netdev - Re: Races in net_rx_action vs netpoll?

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Message-Id: <20070710.224457.95896396.davem@davemloft.net>
Date:	Tue, 10 Jul 2007 22:44:57 -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: Tue, 10 Jul 2007 12:44:31 +0200

> On Tuesday 10 July 2007 00:27, David Miller wrote:
> > I'm happy to entertain this kind of solution, but we really
> > need to first have an interface to change multiple bits
> > at a time in one atomic operation, because by itself this
> > patch doubles the number of atomices we do when starting
> > a NAPI poll.
> 
> Understood. How about the patch below? It takes a similar
> approach, but it puts the onus on the netpoll code
> path rather than the general NAPI case.

Definitely looks more palatable.

> @@ -919,6 +921,14 @@ static inline void netif_rx_complete(str
>  {
>  	unsigned long flags;
>  
> +#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?
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