Re: Linux 5.14

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Aug 30, 2021 at 01:15:37PM -0700, Linus Torvalds wrote:
> On Mon, Aug 30, 2021 at 1:12 PM Guenter Roeck <linux@roeck-us.net> wrote:
> >
> > So far so good, but there is a brand new runtime warning, seen when booting
> > s390 images.
> >
> > [    3.218816] ------------[ cut here ]------------
> > [    3.219010] WARNING: CPU: 1 PID: 0 at kernel/sched/core.c:5779 sched_core_cpu_starting+0x172/0x180
> > [    3.222845] Call Trace:
> > [    3.222992]  [<0000000000186e86>] sched_core_cpu_starting+0x176/0x180
> > [    3.223114] ([<0000000000186dc4>] sched_core_cpu_starting+0xb4/0x180)
> > [    3.223182]  [<00000000001963e4>] sched_cpu_starting+0x2c/0x68
> > [    3.223243]  [<000000000014f288>] cpuhp_invoke_callback+0x318/0x970
> > [    3.223304]  [<000000000014f970>] cpuhp_invoke_callback_range+0x90/0x108
> > [    3.223364]  [<000000000015123c>] notify_cpu_starting+0x84/0xa8
> > [    3.223426]  [<0000000000117bca>] smp_init_secondary+0x72/0xf0
> > [    3.223492]  [<0000000000117846>] smp_start_secondary+0x86/0x90
> >
> > Commit 3c474b3239f12 ("sched: Fix Core-wide rq->lock for uninitialized
> > CPUs") seems to be the culprit. Indeed, the warning is gone after reverting
> > this commit.
> 
> Ouch, not great timing.
> 
> Adding the s390 people to the cc too, just to make sure everybody
> involved is aware.

'Funny' thing, Sven actually tested that on s390. I had already comitted
the patch which is why his tag isn't on the commit:

  https://lkml.kernel.org/r/yt9dy28o8q0o.fsf@linux.ibm.com

Anyway, looks like Thomas found something fishy in their topology code.
Lemme go catch up.