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

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Date:	Fri, 28 Jul 2006 14:26:16 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Ravikiran G Thirumalai <kiran@...lex86.org>
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, 28 Jul 2006, Ravikiran G Thirumalai wrote:

> 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.

Ok.

> Again, if this is indeed a problem (recursion) machine should not boot even,
> when compiled without lockdep, tglx, can you please verify this?

We seem to be fine on that level.

I would still like to see someone thinking through this a bit more.

Allocations via page_alloc_node() may be redirected by cpusets and 
because nodes are low on memory. This means that we get memory on a 
different node than we requested. How does that impact the alien lock 
situation? In particular what happens if the off slab allocation for 
the management object was on a different node from the slab data?
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