Re: [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0.6.8

[Ingo Molnar <mingo@elte.hu>]

* Mark_H_Johnson@raytheon.com <Mark_H_Johnson@raytheon.com> wrote:

> This build appears to run OK and then in the middle of the real time
> tests stops doing useful work (during network test).

weird, the deadlock detector did not trigger, although it is a clear
circular deadlock:

R     ksoftirqd/0/    3 [dffe8020, 105] blocked on: [dfcafc20] {r:0,a:-1,&((sk)->sk_lock.slock)}
.. held by:               rcp/ 4791 [d84bd910, 118]
... acquired at:  ip_send_reply+0x12b/0x250

D             rcp/ 4791 [d84bd910, 118] blocked on: [c03cb900] {r:0,a:-1,ptype_lock}
.. held by:       ksoftirqd/0/    3 [dffe8020, 105]
... acquired at:  netif_receive_skb+0xae/0x330

i.e. ksoftirqd blocked on rcp and rcp blocked on ksoftirqd, cleanly
deadlocking each other.

anyway, does the patch below, ontop of -V0.6.8, fix this type of hang?

	Ingo

--- linux/net/core/dev.c.orig
+++ linux/net/core/dev.c
@@ -1916,7 +1916,9 @@ static void net_rx_action(struct softirq
 		dev = list_entry(queue->poll_list.next,
 				 struct net_device, poll_list);
 
+		rcu_read_lock_read(&ptype_lock);
 		if (dev->quota <= 0 || dev->poll(dev, &budget)) {
+			rcu_read_unlock_read(&ptype_lock);
 			local_irq_disable();
 			list_del(&dev->poll_list);
 			list_add_tail(&dev->poll_list, &queue->poll_list);
@@ -1926,6 +1928,7 @@ static void net_rx_action(struct softirq
 				dev->quota = dev->weight;
 		} else {
 			dev_put(dev);
+			rcu_read_unlock_read(&ptype_lock);
 			local_irq_disable();
 		}