linux-kernel - Re: 2.6.22-rc6 bad page error

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Message-ID: <20070712134606.A10012@jurassic.park.msu.ru>
Date:	Thu, 12 Jul 2007 13:46:06 +0400
From:	Ivan Kokshaysky <ink@...assic.park.msu.ru>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Bob Tracy <rct@...rkin.frus.com>,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
	linux-kernel@...r.kernel.org, linux-alpha@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: 2.6.22-rc6 bad page error

On Wed, Jul 11, 2007 at 06:07:59PM +0100, Hugh Dickins wrote:
> > +	gfp &= ~GFP_DMA;
> 
> The canonical form for this masking, even on arches without HIGHMEM,
> appears to be:
> 	gfp &= ~(__GFP_DMA | __GFP_HIGHMEM);
> But I guess that won't make any actual difference.

As far as I can see, none of 64-bit architectures masks the HIGHMEM
(or any other) bits. It's just not obvious because most of their
"alloc_coherent" routines are hidden in iommu_ops or something like that.

> > +	return __pci_alloc_consistent(dev, size, dma, GFP_ATOMIC);
> 
> I was going to ask you why that needs to be GFP_ATOMIC on Alpha.
> But find you're following the example of asm-generic and others.
> So really should be asking Sparc how it gets away with GFP_KERNEL.

According to DMA-mapping.txt GFP_ATOMIC is mandatory for
pci_alloc_consistent() since it can be called from interrupt context.
So sparc code is probably incorrect...

Ivan.
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