linux-kernel - Re: [BUG] Lockdep recursive locking in kmem_cache

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Message-Id: <1154121608.10196.24.camel@localhost.localdomain>
Date:	Fri, 28 Jul 2006 23:20:08 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Ravikiran G Thirumalai <kiran@...lex86.org>
Cc:	Christoph Lameter <clameter@....com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...radead.org>,
	alokk@...softinc.com
Subject: Re: [BUG] Lockdep recursive locking in kmem_cache_free

On Fri, 2006-07-28 at 14:12 -0700, Ravikiran G Thirumalai wrote:
> On Fri, Jul 28, 2006 at 01:48:33PM -0700, Christoph Lameter wrote:
> > On Fri, 28 Jul 2006, Thomas Gleixner wrote:
> > 
> > > On Fri, 2006-07-28 at 13:36 -0700, Christoph Lameter wrote:
> > > > On Fri, 28 Jul 2006, Thomas Gleixner wrote:
> > > > 
> > > > > Let me know, if you need more info
> > > > 
> > > > What type of NUMA system is this? How many nodes? Is memory exhausted on 
> > > > some so that allocations are redirected? Are cpusets or memory policies
> > > > used to redirect allocations?
> > > 
> > > Dual dual core opteron board, only one CPU brought up. This happens
> > > during bootup, so no special settings involved.
> > 
> > One cpu with two nodes?
> > 
> > > [    0.000000] Bootmem setup node 0 0000000000000000-0000000080000000
> > > [    0.000000] Bootmem setup node 1 0000000080000000-00000000fbff0000
> > 
> > Right two nodes. We may have a special case here of one cpu having to 
> > manage remote memory. Alien cache freeing is likely screwed up in that 
> > case because we cannot have the idea of one processor local to the node 
> > doing the alien cache draining . We have to take the remote lock (no cpu 
> > dedicate to that node).
> 
> Why should there be any problem taking the remote l3 lock?  If the remote
> node does not have cpu that does not mean we cannot take a lock from the
> local node!!! 
> 
> I think current git does not teach lockdep to ignore recursion for
> array_cache->lock when the array_cache->lock are from different cases.  As
> Arjan pointed out, I can see that l3->list_lock is special cased, but I
> cannot find where array_cache->lock is taken care of.
> 
> Again, if this is indeed a problem (recursion) machine should not boot even,
> when compiled without lockdep, tglx, can you please verify this?

It boots witjh lockdep disabled, so lockdep needs some education, which
is not that easy in this case.

	tglx


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