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

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Date:	Fri, 28 Jul 2006 14:12:27 -0700
From:	Ravikiran G Thirumalai <kiran@...lex86.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	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, 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?

Thanks,
Kiran
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