linux-kernel - Re: [PATCH] x86: adjust GFP mask handling for coherent allocations

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Date:	Tue, 27 Oct 2009 09:47:32 +0000
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"FUJITA Tomonori" <fujita.tomonori@....ntt.co.jp>
Cc:	<mingo@...e.hu>, <yinghai@...nel.org>, <tglx@...utronix.de>,
	<tiwai@...e.de>, <linux-kernel@...r.kernel.org>,
	<jbarnes@...tuousgeek.org>, <hpa@...or.com>
Subject: Re: [PATCH] x86: adjust GFP mask handling for coherent
	 allocations

>>> FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> 27.10.09 10:37 >>>
>On Tue, 27 Oct 2009 09:23:38 +0000
>"Jan Beulich" <JBeulich@...ell.com> wrote:
>
>> Because there's quite a few of them - just search for callers of
>> dma_alloc_coherent() passing NULL as the first argument. Of course
>> I'd rather see the fallback gone, but I think this requires cooperation
>> from/action taken by the driver maintainers first. A first step might be
>> to add a WRN_ON() for that case, but I don't see it being reasonable
>> to eliminate the fallback right away. Hence, with it having got broken
>> in .26 I think it is reasonable to fix it for the time being.
>
>Well, the most of them are drivers that nobody cares about (uses).
>
>What drivers did you hit this problem with?

drivers/firmware/dell_rbu.c (on .27.x, and in particular with the derivation
of __GFP_NORETRY from __GFP_DMA, which fortunately doesn't exist in
newer kernels anymore).

>We've lived with the current code for some years so this problem isn't
>urgent at all. Please don't add another workaround for broken code.
>Let's put WARN_ON for callers that use NULL and see who complains.

Jan

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