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

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Message-ID: <2375c9f91003120059g771d162fxefc21beb2ab17b4d@mail.gmail.com>
Date:	Fri, 12 Mar 2010 16:59:33 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	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 4:07 PM, David Miller <davem@...emloft.net> wrote:
> From: Américo Wang <xiyou.wangcong@...il.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 softirq context.
>
> Normally, netif_receive_skb() is invoked from softirq context.
>
> However, via netpoll it can be invoked essentially from any context.
>
> But, when this happens, the networking receive path makes amends such
> that this works fine.  That's what the netpoll_receive_skb() check in
> netif_receive_skb() is for.  That check makes it bail out early 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.

Thanks much, David!
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