From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: 2.6.34-rc1: rcu lockdep bug?
Date: Fri, 12 Mar 2010 14:37:38 +0100
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Cc: David Miller <davem@davemloft.net>, paulmck@linux.vnet.ibm.com,
	peterz@infradead.org, linux-kernel@vger.kernel.org,
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To: =?ISO-8859-1?Q?Am=E9rico?= Wang <xiyou.wangcong@gmail.com>
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Le vendredi 12 mars 2010 =C3=A0 21:11 +0800, Am=C3=A9rico Wang a =C3=A9=
crit :

> Oh, but lockdep complains about rcu_read_lock(), it said
> rcu_read_lock() can't be used in softirq context.
>=20
> 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().