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Date: Fri, 12 Mar 2010 15:56:03 +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>, Linux Kernel Network Developers <netdev@...r.kernel.org> Subject: Re: 2.6.34-rc1: rcu lockdep bug? (Cc'ing netdev) On Fri, Mar 12, 2010 at 12:17 AM, Américo Wang <xiyou.wangcong@...il.com> wrote: > 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. > 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. Paul, what do you think? Thank you. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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