From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?UTF-8?Q?Am=C3=A9rico_Wang?= <xiyou.wangcong@gmail.com>
Subject: Re: 2.6.34-rc1: rcu lockdep bug?
Date: Fri, 12 Mar 2010 21:11:02 +0800
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Cc: David Miller <davem@davemloft.net>, paulmck@linux.vnet.ibm.com,
	peterz@infradead.org, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org
To: Eric Dumazet <eric.dumazet@gmail.com>
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On Fri, Mar 12, 2010 at 7:11 PM, Eric Dumazet <eric.dumazet@gmail.com> =
wrote:
> Le vendredi 12 mars 2010 =C3=A0 16:59 +0800, Am=C3=A9rico Wang a =C3=A9=
crit :
>> On Fri, Mar 12, 2010 at 4:07 PM, David Miller <davem@davemloft.net> =
wrote:
>> > From: Am=C3=A9rico Wang <xiyou.wangcong@gmail.com>
>> > Date: Fri, 12 Mar 2010 15:56:03 +0800
>> >
>> >> Ok, after decoding the lockdep output, it looks like that
>> >> netif_receive_skb() should call rcu_read_lock_bh() instead of rcu=
_read_lock()?
>> >> But I don't know if all callers of netif_receive_skb() are in sof=
tirq context.
>> >
>> > Normally, netif_receive_skb() is invoked from softirq context.
>> >
>> > However, via netpoll it can be invoked essentially from any contex=
t.
>> >
>> > But, when this happens, the networking receive path makes amends s=
uch
>> > that this works fine. =C2=A0That's what the netpoll_receive_skb() =
check in
>> > netif_receive_skb() is for. =C2=A0That check makes it bail out ear=
ly if the
>> > call to netif_receive_skb() is via a netpoll invocation.
>> >
>>
>> Oh, I see. This means we should call rcu_read_lock_bh() instead.
>> If Paul has no objections, I will send a patch for this.
>>
>
> Nope, its calling rcu_read_lock() from interrupt context and it shoul=
d
> stay as is (we dont need to disable bh, this has a cpu cost)
>

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

Am I missing something?