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

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Message-ID: <20070624083849.GA19079@flint.arm.linux.org.uk>
Date:	Sun, 24 Jun 2007 09:38:50 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Christoph Lameter <clameter@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 07:39:33PM +0100, Hugh Dickins wrote:
> On Fri, 22 Jun 2007, Christoph Lameter wrote:
> > 
> > Add VM_BUG_ON in case someone uses page_mapping on a slab page
> > 
> > Detect slab objects being passed to the page oriented functions of the VM.
> > 
> > It is not sufficient to simply return NULL because the functions calling
> > page_mapping may depend on other items of the page_struct also to be setup
> > properly. Moreover the slab object may not be properly aligned. The page 
> > orientedfunctions of the VM expect to operate on page aligned, page sized 
> > objects. operations on objects straddling page boundaries may only affect 
> > the objects partially which may lead to surprising results.
> > 
> > It is better to detect eventually remaining uses and eliminate them.
> > 
> > Signed-off-by: Christoph Lameter <clameter@....com>
> 
> I'm quite happy with this approach for 2.6.23-rc, along with your ARM
> dma_map patch which (if I understood aright) rmk approved.

I didn't approve it.  Please re-read my reply - there are still some
unanswered questions in it which _really_ need answering.

The report talks about the AT91 machines.  These machines do not have
cache coherent DMA.  Therefore, the code being patched should be
optimised away by the compiler. *Or* we have even bigger problems.

Please forward the original problem report.

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