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

From: Guenter Roeck
Date: Wed Mar 16 2016 - 22:36:53 EST

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:
[ ... ]
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.


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.


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.