linux-kernel - Re: [PATCH] fix crash when using XFS on loopback

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Message-ID: <alpine.LRH.2.02.1401041451350.21108@file01.intranet.prod.int.rdu2.redhat.com>
Date:	Sat, 4 Jan 2014 14:55:55 -0500 (EST)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	John David Anglin <dave.anglin@...l.net>
cc:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andi Kleen <ak@...ux.intel.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@....fi>, linux-kernel@...r.kernel.org,
	linux-parisc@...r.kernel.org
Subject: Re: [PATCH] fix crash when using XFS on loopback

On Sat, 4 Jan 2014, John David Anglin wrote:

> On 4-Jan-14, at 12:45 PM, Mikulas Patocka wrote:
> 
> > * flush_dcache_page asks for the list of userspace mappings, however that
> > page->mapping field is reused by the slab subsystem for a different
> > purpose. This causes the crash.
> 
> I'd noticed the other day that the parisc implementation of
> flush_dcache_page()
> should return if "!mapping || mapping != page->mapping" is true.  This would
> have avoided crash.
> 
> Dave

I think no.

page_mapping returns NULL if the page has only anonymous mapping and it is 
not placed in the swap cache. In this case, you need to flush the kernel 
cache.

Maybe you could skip cache flush if the page is neither anonymous nor 
file-backed, but I haven't seen this condition in other architectures' 
flush_dcache_page.

Mikulas
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