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

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Message-ID: <1463749762.18194.288.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Fri, 20 May 2016 06:09:22 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	John Fastabend <john.fastabend@...il.com>,
	Kevin Athey <kda@...gle.com>,
	Xiaotian Pei <xiaotian@...gle.com>
Subject: Re: [RFC net-next] net: sched: do not acquire qdisc spinlock in
 qdisc/class stats dump

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 */