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

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Message-ID: <20100313053356.GC3704@hack>
Date:	Sat, 13 Mar 2010 13:33:56 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	David Miller <davem@...emloft.net>, paulmck@...ux.vnet.ibm.com,
	peterz@...radead.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: 2.6.34-rc1: rcu lockdep bug?

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.

Thanks!
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