linux-kernel - Re: linux-next: Tree for Mar 14 (mips qemu failure bisected)

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Message-ID: <56EA1839.8010807@roeck-us.net>
Date:	Wed, 16 Mar 2016 19:36:41 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Qais Yousef <qsyousef@...il.com>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...ux-mips.org
Subject: Re: linux-next: Tree for Mar 14 (mips qemu failure bisected)

On 03/16/2016 03:17 PM, Qais Yousef wrote:
> On 16/03/2016 20:27, Qais Yousef wrote:
>>
>>
>> On 16/03/2016 13:22, Guenter Roeck wrote:
>>> On Tue, Mar 15, 2016 at 05:17:13PM -0700, Guenter Roeck wrote:
>>>> On Tue, Mar 15, 2016 at 09:55:06PM +0000, Qais Yousef wrote:
>>>>> Hi Guenter,
>>>>>
>>> [ ... ]
>>>>>>> Qemu test results:
>>>>>>>     total: 96 pass: 69 fail: 27
>>>>>>> Failed tests:
>>>>>> [ ... ]
>>>>>>>     mips:mips_malta_smp_defconfig
>>>>>> I bisected this failure to commit bb11cff327e54 ("MIPS: Make smp CMP, CPS and MT
>>>>>> use the new generic IPI functions". Bisect log is attached.
>>>>> Thanks for bisecting this. I tested this on a real Malta system but not
>>>>> qemu. I'll try to reproduce.
>>>>>
>>>> I run the tests with only a single CPU core enabled. Maybe that causes
>>>> problems with your code ?
>>>>
>>> I ran another qemu test (this time on mainline) with "-smp 2", but the only
>>> difference is that the image now gets stuck even earlier.
>>>
>>> Also, I ran another set of bisects, this time with both mips and mips64
>>> on mainline (after your patch landed), with the same results.
>>>
>>> Guenter
>>>
>>
>> OK thanks for the info. The offending commit just enables using quite a few of the newly added code before that. So the problem could be in any of the newly added code.
>>
>> Unfortunately I can only look at this during my limited time in the evening and I have to setup my system to compile and run this, so I won't be able to get to the bottom of this as fast as I'd like to.
>>
>> Qais
>
> OK I was up and running faster than I thought I would be. Can you confirm that you're hitting a BUG_ON() in mips_smp_ipi_init()?
>
> What I see is that BUG_ON() is hit because we couldn't find an ipidomain to allocate the ipis from. The reason of whih is that the qemu malta machine doesn't have a GIC though the config is compiled with GIC on. Also if I remember correctly qemu malta doesn't really support SMP. I think that was the reason I never ran this on qemu.

Turns out MIPS_GIC is auto-selected by MIPS_MALTA, so I can not just unconfigure it.
Too bad. That means if your patch isn't accepted, I'll have to drop the mips
SMP build runtime tests, unless you have a better idea.

Thanks,
Guenter