linux-kernel - Re: [PATCH] dma-mapping: Remove WARN_ON in dma_free

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Message-ID: <4BB113E7.4050200@zytor.com>
Date:	Mon, 29 Mar 2010 13:56:07 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Stefan Bader <stefan.bader@...onical.com>
CC:	Matthew Wilcox <matthew@....cx>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, James.Bottomley@...e.de
Subject: Re: [PATCH] dma-mapping: Remove WARN_ON in dma_free_coherent

On 03/29/2010 01:50 PM, Stefan Bader wrote:
> Matthew Wilcox wrote:
>> On Mon, Mar 29, 2010 at 08:09:21PM +0200, Stefan Bader wrote:
>>> But it seems modifying that driver would be a bigger effort and maybe
>>> not really worthwile as it is a rather old driver. On the other side
>>> I was told [1] that this WARN_ON applies only to ARM which could sleep
>>> in the free path and it is just bogus for X86. As the code is in
>>> arch/x86 it would never be used for anything else than X86 and if
>>> its truely bogus on X86, couldn't it get removed?
>>
>> My suggestion was that you remove it from the Ubuntu kernel, not submit
>> it upstream.
>>
> No, I did not want to give that impression. But my rational was, that if this is
>  really a warning that has no meaning on X86, then why should it stay in code
> that is x86 only. And then why should that not go upstream.
> When I tried following the code, it looked like this was carried forward for
> quite a while and maybe it just stayed because nobody noticed it.
> But with KVM using that scsi driver, other distros might see the same bogus
> warning and then it would be beneficial for all to just remove it.
> If Ingo or hpa say it is needed, ok. But its at least worth a go.
> 


-	WARN_ON(irqs_disabled());       /* for portability */
                                           ^^^^^^^^^^^^^^^

It's there to keep people from writing their drivers incorrectly,
testing them on x86 only, and then pushing them upstream.

Nacked-by: H. Peter Anvin <hpa@...or.com>

	-hpa
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