netpoll trapped question

[Jeff Moyer]

Hi, Matt,

This part of the netpoll trapped logic seems suspect to me, from
include/linux/netdevice.h:

static inline void netif_wake_queue(struct net_device *dev)
{
#ifdef CONFIG_NETPOLL_TRAP
	if (netpoll_trap())
		return;
#endif
	if (test_and_clear_bit(__LINK_STATE_XOFF, &dev->state))
		__netif_schedule(dev);
}

static inline void netif_stop_queue(struct net_device *dev)
{
#ifdef CONFIG_NETPOLL_TRAP
	if (netpoll_trap())
		return;
#endif
	set_bit(__LINK_STATE_XOFF, &dev->state);
}

This looks buggy.  Network drivers are now not able to stop the queue when
they run out of Tx descriptors.  I think the __netif_schedule is okay to do
in the context of netpoll, and certainly a set_bit is okay.  Why are these
hooks in place?  I've tested alt-sysrq-t over netconsole and also netdump
with these #ifdef's removed, and things work correctly.  Compare this with
alt-sysrq-t hanging the system with these tests in place.  If I run netdump
with this logic still in place, I get the following messages from the tg3
driver:

  eth0: BUG! Tx Ring full when queue awake!

Shall I send a patch, or have I missed something?

-Jeff
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