Re: serious netpoll bug w/NAPI

["David S. Miller" <davem@xxxxxxxxxxxxx>]

On Tue, 15 Feb 2005 21:07:22 -0800
Matt Mackall <mpm@xxxxxxxxxxx> wrote:

> Because dev->np->poll_lock now serializes all access to ->poll (when
> netpoll is enabled on said device).

I think there is still a problem.

Sure, we won't recurse into ->poll(), but instead we'll loop forever
in netpoll_send_skb() in this case when netif_queue_stopped() is true.
We can't get into the ->poll() routine, so the TX queue can't make
forward progress, yet we keep looping to the "repeat" label over
and over again.

So we've replaced a crash via ->poll() re-entry with a deadlock
in netpoll_send_skb() :-)

I also think that taking a global spinlock for every ->poll()
call is a huge price to pay on SMP.