Re: [RFC net-next] net: sched: do not acquire qdisc spinlock in qdisc/class stats dump

[Eric Dumazet]

On Fri, 2016-05-20 at 06:01 -0700, Eric Dumazet wrote:

> Tricky, since sch_direct_xmit() releases the qdisc spinlock and grabs it
> again, while owning the ' running seqcount'
> 
> Needs more LOCKDEP tricks ;)
> 

That would be :

@@ -137,10 +137,10 @@ int sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q,
 
                HARD_TX_UNLOCK(dev, txq);
        } else {
-               spin_lock(root_lock);
+               spin_lock_nested(root_lock, SINGLE_DEPTH_NESTING);
                return qdisc_qlen(q);
        }
-       spin_lock(root_lock);
+       spin_lock_nested(root_lock, SINGLE_DEPTH_NESTING);
 
        if (dev_xmit_complete(ret)) {
                /* Driver sent out skb successfully or skb was consumed */