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

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Date:	Fri, 12 Mar 2010 14:37:38 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	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?

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().

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