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Subject: Re: 2.6.34-rc1: rcu lockdep bug?
From: Eric Dumazet <eric.dumazet@gmail.com>
To: =?ISO-8859-1?Q?Am=E9rico?= Wang <xiyou.wangcong@gmail.com>
Cc: David Miller <davem@davemloft.net>, paulmck@linux.vnet.ibm.com,
       peterz@infradead.org, linux-kernel@vger.kernel.org,
       netdev@vger.kernel.org
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Date: Fri, 12 Mar 2010 12:11:16 +0100
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Le vendredi 12 mars 2010 à 16:59 +0800, Américo Wang a écrit :
> On Fri, Mar 12, 2010 at 4:07 PM, David Miller <davem@davemloft.net> wrote:
> > From: Américo Wang <xiyou.wangcong@gmail.com>
> > Date: Fri, 12 Mar 2010 15:56:03 +0800
> >
> >> Ok, after decoding the lockdep output, it looks like that
> >> netif_receive_skb() should call rcu_read_lock_bh() instead of rcu_read_lock()?
> >> But I don't know if all callers of netif_receive_skb() are in softirq context.
> >
> > Normally, netif_receive_skb() is invoked from softirq context.
> >
> > However, via netpoll it can be invoked essentially from any context.
> >
> > But, when this happens, the networking receive path makes amends such
> > that this works fine.  That's what the netpoll_receive_skb() check in
> > netif_receive_skb() is for.  That check makes it bail out early if the
> > call to netif_receive_skb() is via a netpoll invocation.
> >
> 
> Oh, I see. This means we should call rcu_read_lock_bh() instead.
> If Paul has no objections, I will send a patch for this.
> 

Nope, its calling rcu_read_lock() from interrupt context and it should
stay as is (we dont need to disable bh, this has a cpu cost)