* Ingo Molnar <[email protected]> wrote:
> hm, i got a new one:
>
> ============================================
> [ BUG: circular locking deadlock detected! ]
> --------------------------------------------
> sshd/28997 is trying to acquire lock:
> (&sk->sk_lock.slock){-+}, at: [<c0c6be28>] packet_rcv+0xbf/0x34b
>
> but task is already holding lock:
> (&dev->xmit_lock){-+}, at: [<c0bb04ec>] qdisc_restart+0x46/0x207
>
> which lock already depends on the new lock,
> which could lead to circular deadlocks!
>
> the dependency chain (in reverse order) is:
> -> #2 (&dev->xmit_lock){-+}: [<c0bb04ec>] qdisc_restart+0x46/0x207
> -> #1 (&dev->queue_lock){-+}: [<c0b98137>] dev_queue_xmit+0xc3/0x21e
> -> #0 (&sk->sk_lock.slock){-+}: [<c0c6be28>] packet_rcv+0xbf/0x34b
i think this might be a false positive, caused by my (ill-advised)
change below? [i did the change to clean up an unlock ordering
assymetry, but apparently i thus also introduced the xmit_lock ->
queue_lock dependency.]
Ingo
Index: linux/net/sched/sch_generic.c
===================================================================
--- linux.orig/net/sched/sch_generic.c
+++ linux/net/sched/sch_generic.c
@@ -98,6 +98,8 @@ int qdisc_restart(struct net_device *dev
/* Dequeue packet */
if ((skb = q->dequeue(q)) != NULL) {
unsigned nolock = (dev->features & NETIF_F_LLTX);
+ /* release queue */
+ spin_unlock(&dev->queue_lock);
/*
* When the driver has LLTX set it does its own locking
* in start_xmit. No need to add additional overhead by
@@ -121,9 +123,11 @@ int qdisc_restart(struct net_device *dev
kfree_skb(skb);
if (net_ratelimit())
printk(KERN_DEBUG "Dead loop on netdevice %s, fix it urgently!\n", dev->name);
+ spin_lock(&dev->queue_lock);
return -1;
}
__get_cpu_var(netdev_rx_stat).cpu_collision++;
+ spin_lock(&dev->queue_lock);
goto requeue;
}
/* Remember that the driver is grabbed by us. */
@@ -131,8 +135,6 @@ int qdisc_restart(struct net_device *dev
}
{
- /* And release queue */
- spin_unlock(&dev->queue_lock);
if (!netif_queue_stopped(dev)) {
int ret;
-
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