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Date: Fri, 12 Mar 2010 00:17:51 +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>,
       Peter Zijlstra <peterz@infradead.org>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: 2.6.34-rc1: rcu lockdep bug?
Message-ID: <20100311161751.GA3804@hack>
References: <2375c9f91003110205v1d7f00bfk89472cb11bd985d3@mail.gmail.com> <20100311134556.GA6344@linux.vnet.ibm.com>
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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!