netdev - Re: 2.6.34-rc1: rcu lockdep bug?

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Message-ID: <20100313215838.GB6805@linux.vnet.ibm.com>
Date:	Sat, 13 Mar 2010 13:58:38 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>, peterz@...radead.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: 2.6.34-rc1: rcu lockdep bug?

On Sat, Mar 13, 2010 at 01:33:56PM +0800, Américo Wang wrote:
> On Fri, Mar 12, 2010 at 02:37:38PM +0100, Eric Dumazet wrote:
> >Le vendredi 12 mars 2010 à 21:11 +0800, Américo Wang a écrit :
> >
> >> Oh, but lockdep complains about rcu_read_lock(), it said
> >> rcu_read_lock() can't be used in softirq context.
> >> 
> >> Am I missing something?
> >
> >Well, lockdep might be dumb, I dont know...
> >
> >I suggest you read rcu_read_lock_bh kernel doc :
> >
> >/**
> > * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical
> >section
> > *
> > * This is equivalent of rcu_read_lock(), but to be used when updates
> > * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
> > * consider completion of a softirq handler to be a quiescent state,
> > * a process in RCU read-side critical section must be protected by
> > * disabling softirqs. Read-side critical sections in interrupt context
> > * can use just rcu_read_lock().
> > *
> > */
> >
> >
> >Last sentence being perfect :
> >
> >Read-side critical sections in interrupt context
> >can use just rcu_read_lock().
> >
> 
> Yeah, right, then it is more likely to be a bug of rcu lockdep.
> Paul is looking at it.

Except that it seems to be working correctly for me...

							Thanx, Paul
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