linux-kernel - Re: Oops in a driver while using SLUB as a SLAB allocator

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Date:	Fri, 22 Jun 2007 21:18:17 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Hugh Dickins <hugh@...itas.com>,
	Christoph Lameter <clameter@....com>,
	Nicolas Ferre <nicolas.ferre@....atmel.com>,
	ARM Linux Mailing List 
	<linux-arm-kernel@...ts.arm.linux.org.uk>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Marc Pignat <marc.pignat@...s.ch>,
	Andrew Victor <andrew@...people.com>,
	Pierre Ossman <drzeus@...eus.cx>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Oops in a driver while using SLUB as a SLAB allocator

On Fri, Jun 22, 2007 at 09:40:45AM -0700, Linus Torvalds wrote:
> 
> 
> On Fri, 22 Jun 2007, Hugh Dickins wrote:
> >
> > On Thu, 21 Jun 2007, Christoph Lameter wrote:
> > 
> > > Maybe this will address the issue on ARM?
> > 
> > Looks like it would indeed address the immediate issue on ARM -
> > IF they've no particular reason to be using kmalloc there.
> 
> I think the right thing to do is do both of these things. I already 
> applied Hugh's patch - it seemed like a total nobrainer to do at this 
> stage in the 2.6.22 -rc series. But that doesn't mean that we should not 
> _also_ look at "flush_dcache_page()" users.

Note, however, that the use of flush_dcache_page() on allocations
derived from dma_alloc_coherent() is undefined and unpredictable.

dma_alloc_coherent() may return a remapped virtual address which
would be invalid for things like virt_to_page() to operate on.

So the fact that dma_alloc_coherent() returning something that was
kmalloc'd and then causing flush_dcache_page() to oops is actually
a sign that there's far deeper problems.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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