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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: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       David Miller <davem@davemloft.net>, peterz@infradead.org,
       linux-kernel@vger.kernel.org, netdev@vger.kernel.org
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Date: Mon, 15 Mar 2010 11:41:03 +0100
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Le lundi 15 mars 2010 à 18:12 +0800, Américo Wang a écrit :
> On Mon, Mar 15, 2010 at 6:04 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > Le lundi 15 mars 2010 à 17:39 +0800, Américo Wang a écrit :
> >
> >>
> >> Ok, I think I found what lockdep really complains about, it is that we took
> >> spin_lock in netpoll_poll_lock() which is in hardirq-enabled environment,
> >> later, we took another spin_lock with spin_lock_irqsave() in netpoll_rx(),
> >> so lockdep thought we broke the locking rule.
> >>
> >> I don't know why netpoll_rx() needs irq disabled, it looks like that no one
> >> takes rx_lock in hardirq context. So can we use spin_lock(&rx_lock)
> >> instead? Or am I missing something here? Eric? David?
> >
> > I am a bit lost.
> >
> > Could you give the complete picture, because I cannot find it in my
> > netdev archives.
> >
> 
> Sure, sorry for this.
> 
> Here is the whole thread:
> 
> http://lkml.org/lkml/2010/3/11/100

OK thanks

netpoll_rx() can be called from hard irqs (netif_rx()), so rx_lock
definitly needs irq care.

netpoll_poll_lock() does take a spinlock with irq enabled, but its not
rx_lock, its napi->poll_lock.

I dont see what could be the problem, is it reproductible with vanilla
kernel ?