linux-kernel - Re: 2.6.34-rc1: rcu lockdep bug?

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Message-ID: <20100311161751.GA3804@hack>
Date:	Fri, 12 Mar 2010 00:17:51 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.34-rc1: rcu lockdep bug?

On Thu, Mar 11, 2010 at 05:45:56AM -0800, Paul E. McKenney wrote:
>On Thu, Mar 11, 2010 at 06:05:38PM +0800, Américo Wang wrote:
>> Hello, Paul and Peter,
>> 
>> Attached is the lockdep warning that I triggered today.
>> 
>> I am not sure if this is a bug of rcu lockdep, because I am
>> testing my patch when this occurred. However, in the backtrace,
>> there is none of the functions that I touched, weird.
>> 
>> So, please help to check if this is a bug of rcu lockdep.
>
>This sort of thing is caused by acquiring the same lock with softirq
>(AKA BH) blocked and not, which can result in self-deadlock.
>
>There was such a bug in the RCU lockdep stuff in -tip, but it has long
>since been fixed.  If you were seeing that bug, rcu_do_batch() would
>be on the stack, which it does not appear to be.
>
>So does your patch involve the usbfs_mutex?  Or attempt to manipulate
>vfs/fs state from withing networking softirq/BH context?
>

Nope, it is a patch for netpoll, nothing related with usb, nor vfs.

Thanks much!

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