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

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Date:	Wed, 16 Mar 2016 22:17:41 +0000
From:	Qais Yousef <qsyousef@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
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 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.

I'm not sure what's the best way forward here. I can add a check to 
verify gic_present inside this function and return early. Patch attached.

Ralf, thoughts?

Thanks,
Qais

View attachment "0001-MIPS-Fix-broken-malta-qemu.patch" of type "text/plain" (1410 bytes)