Re: [PATCH] netpoll: break recursive loop in netpoll rx path

[Matt Mackall <mpm@selenic.com>]

On Mon, Jun 12, 2006 at 11:40:29AM -0400, Neil Horman wrote:
> Hey there-
> 	the netpoll system currently has a rx to tx path via:
> netpoll_rx
>  __netpoll_rx
>   arp_reply
>    netpoll_send_skb
>     dev->hard_start_tx
> 
> 	This rx->tx loop places network drivers at risk of
> inadvertently causing a deadlock or BUG halt by recursively trying
> to acquire a spinlock that is used in both their rx and tx paths
> (this problem was origionally reported to me in the 3c59x driver,
> which shares a spinlock between the boomerang_interrupt and
> boomerang_start_xmit routines).

Grumble.

> This patch breaks this loop, by queueing arp frames, so that they
> can be responded to after all receive operations have been
> completed. Tested by myself and the reported with successful
> results.

Tested how? kgdb?

> +	if (likely(npi))
> +		while ((skb = skb_dequeue(&npi->arp_tx)) != NULL)
> +			arp_reply(skb);
> +

Assignment inside tests is frowned upon. I'd prefer pulling this out
to its own function too.


Mathematics is the supreme nostalgia of our time.