linux-kernel - Re: xfs lockdep trace after unlink

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Message-ID: <20131008215947.GA8915@redhat.com>
Date:	Tue, 8 Oct 2013 17:59:47 -0400
From:	Dave Jones <davej@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>, xfs@....sgi.com
Subject: Re: xfs lockdep trace after unlink

On Tue, Oct 08, 2013 at 02:39:10PM -0700, Paul E. McKenney wrote:
 > On Tue, Oct 08, 2013 at 05:20:56PM -0400, Dave Jones wrote:
 > > I was deleting a kernel tree, when this happened..
 > > RCU, or xfs ?
 > > 
 > > BUG: MAX_LOCKDEP_CHAINS too low!
 > 
 > I have to ask...  What happens when you bump up MAX_LOCKDEP_CHAINS?

We eat up a even more memory I guess.

kernel/lockdep_internals.h:#define MAX_LOCKDEP_CHAINS_BITS	15
kernel/lockdep_internals.h:#define MAX_LOCKDEP_CHAINS	(1UL << MAX_LOCKDEP_CHAINS_BITS)

I had to increase MAX_LOCKDEP_ENTRIES on my local tree already because
I was hitting that limit. 

 > There is a patch to avoid an RCU/scheduler/perf deadlock, which may
 > be found below.  But this stack doesn't look to me to be matching that
 > deadlock.

I'll add that to my tree until it gets mainlined.

thanks,

	Dave

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