linux-kernel - Re: sparc64: Build failure due to commit f1600e549b94 (sparc: Make sparc64 use scalable lib/iommu-common.c functions)

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Date:	Mon, 20 Apr 2015 19:32:33 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Michael Ellerman <mpe@...erman.id.au>,
	David Miller <davem@...emloft.net>
CC:	sowmini.varadhan@...cle.com, benh@...nel.crashing.org,
	aik@....ibm.com, anton@....ibm.com, paulus@...ba.org,
	linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org, schwidefsky@...ibm.com,
	heiko.carstens@...ibm.com, linux-s390@...r.kernel.org,
	linux390@...ibm.com
Subject: Re: sparc64: Build failure due to commit f1600e549b94 (sparc: Make
 sparc64 use scalable lib/iommu-common.c functions)

On 04/20/2015 06:54 PM, Michael Ellerman wrote:
> On Mon, 2015-04-20 at 12:50 -0400, David Miller wrote:
>> From: Guenter Roeck <linux@...ck-us.net>
>> Date: Mon, 20 Apr 2015 09:44:31 -0700
>>
>>> On Mon, Apr 20, 2015 at 12:25:19PM -0400, David Miller wrote:
>>>> From: Guenter Roeck <linux@...ck-us.net>
>>>> Date: Sun, 19 Apr 2015 22:17:21 -0700
>>>>
>>>>> The debug option is intended for all _other_ architectures, to
>>>>> ensure that changes made for those don't break alpha/s390
>>>>> builds. alpha/s390 have ARCH_NEEDS_WEAK_PER_CPU and don't need the
>>>>> debug option.
>>>>
>>>> Ironically this would not create a build failure for the architectures
>>>> where this matters, because only powerpc has the like named percpu
>>>> symbol.
>>>>
>>>> So it's not really meeting the stated objective in this case.
>>>
>>> Yes, that is correct; it can only find problems in non-architecture
>>> code, and on the downside produces false positives and thus build errors
>>> like this one.
>>>
>>> Which makes the fix a bit philosophical. Rename iommu_pool_hash in
>>> iommu-common, or drop DEBUG_FORCE_WEAK_PER_CPU. I would rename
>>> iommu_pool_hash, but that is just me. Ultimately, I don't really
>>> care one way or another, as long as the problem gets fixed.
>>
>> If nightly builds of s390 and alpha, the two platforms where this
>> matters, are being done as reported in this thread, then I really
>> don't see the value in DEBUG_FORCE_WEAK_PER_CPU.

Me not either, but, as you say, that is a different discussion.

>
> We do an s390 allmodconfig for every linux-next release:
>
>    http://kisskb.ellerman.id.au/kisskb/target/573/
>
> And also for Linus' tree:
>
>    http://kisskb.ellerman.id.au/kisskb/target/568/
>
> We don't have alpha allmodconfig enabled, though we could, but we do build the
> defconfig:
>
>    http://kisskb.ellerman.id.au/kisskb/target/2499/
>    http://kisskb.ellerman.id.au/kisskb/target/2494/
>
I cover alpha:allmodconfig in my builds for -next, mainline, as well as all
kernel.org stable releases and release candidates. This discussion is a good
argument for enabling s390:allmodconfig as well.

> So I think that should be sufficient to catch any percpus that are introduced
> in generic code with the same name as s390/alpha variables.
>
Yes, but unfortunately only after the fact, though I don't see a means
to avoid that.

>
>> But I guess that's a more involved longer-term discussion and I guess
>> I'll apply Sowmini's patches for now.
>
Thanks!

Guenter

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