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

[Guenter Roeck]

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()?

Most likely, but mips is one of the qemu emulations which simply hang if there is a crash,
without a log message, and I have not been able to figure out a command line that gives me
the actual crash log.

> 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.
Idea is to run the SMP build, not really a multi-core machine.

> 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.

With your patch I get

WARNING: CPU: 0 PID: 1 at arch/mips/kernel/smp.c:251 mips_smp_ipi_init+0x3c/0x1b0()

and the boot continues.

If Ralf accepts it, feel free to add

Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>

though I'll probably adjust my configuration to drop GIC from it (if that is possible).

Thanks a lot for looking into this!

Guenter