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Date: Wed, 20 Jul 2011 09:00:41 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
Subject: Re: possible recursive locking detected cache_alloc_refill() +
 cache_flusharray()
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References: <20110716211850.GA23917@breakpoint.cc>  <alpine.LFD.2.02.1107172333340.2702@ionos>  <alpine.DEB.2.00.1107201619540.3528@tiger> <1311168638.5345.80.camel@twins> <alpine.DEB.2.00.1107201642500.4921@tiger>
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To: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Thomas Gleixner <tglx@linutronix.de>, Sebastian Siewior <sebastian@breakpoint.cc>, Matt Mackall <mpm@selenic.com>, linux-mm@kvack.org

On Wed, 20 Jul 2011, Pekka Enberg wrote:

> So what exactly is the lockdep complaint above telling us? We're holding on to
> l3->list_lock in cache_flusharray() (kfree path) but somehow we now entered
> cache_alloc_refill() (kmalloc path!) and attempt to take the same lock or lock
> in the same class.
>
> I am confused. How can that happen?

I guess you need a slab with CFLGS_OFF_SLAB metadata management. Then slab
does some recursive things doing allocations and free for metadata while
allocating larger objects.

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