linux-kernel - Re: mm: slub: gpf in deactivate

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Message-ID: <alpine.DEB.2.10.1403251150330.16870@nuc>
Date:	Tue, 25 Mar 2014 11:51:59 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Sasha Levin <sasha.levin@...cle.com>
cc:	Pekka Enberg <penberg@...nel.org>, Matt Mackall <mpm@...enic.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: mm: slub: gpf in deactivate_slab

On Tue, 25 Mar 2014, Sasha Levin wrote:

> I have a lead on this. Consider the following:
>
>   kmem_cache_alloc
> 	__slab_alloc
> 		local_irq_save()
> 		deactivate_slab
> 			__cmpxchg_double_slab
> 				slab_unlock
> 					__bit_spin_unlock
> 						preempt_enable
> 		[ Page Fault ]
>
> With this trace, it manifests as a "BUG: sleeping function called from invalid
> context at arch/x86/mm/fault.c" on a might_sleep() in the page fault handler
> (which is an issue on it's own), but I suspect it's also the cause of the
> trace
> above - preemption enabled and a race that removed the page.
>
> Could someone confirm please?

The preempt count is incremented earlier in bit_spin_lock so the
preempt_enable() should not do anything.

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