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Date: Mon, 15 Mar 2010 09:08:02 +0800
From: =?utf-8?Q?Am=C3=A9rico?= Wang <xiyou.wangcong@gmail.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: =?utf-8?Q?Am=C3=A9rico?= Wang <xiyou.wangcong@gmail.com>,
       Eric Dumazet <eric.dumazet@gmail.com>,
       David Miller <davem@davemloft.net>, peterz@infradead.org,
       linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: 2.6.34-rc1: rcu lockdep bug?
Message-ID: <20100315010802.GB2735@hack>
References: <20100311134556.GA6344@linux.vnet.ibm.com> <20100311161751.GA3804@hack> <2375c9f91003112356g1b4164e4pb5f63f0e0e2f310a@mail.gmail.com> <20100312.000705.225033546.davem@davemloft.net> <2375c9f91003120059g771d162fxefc21beb2ab17b4d@mail.gmail.com> <1268392276.3141.4.camel@edumazet-laptop> <2375c9f91003120511j6f33592cl12cb2617a27351ec@mail.gmail.com> <1268401058.3141.9.camel@edumazet-laptop> <20100313053356.GC3704@hack> <20100313215838.GB6805@linux.vnet.ibm.com>
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On Sat, Mar 13, 2010 at 01:58:38PM -0800, Paul E. McKenney wrote:
>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...
>

Hmm, then I am confused. The only possibility here is that this is
a lockdep bug...

Thanks for your help!