Re: [PATCH 1/2] sched/idle: Fix arch_cpu_idle() vs tracing

Guenter Roeck
2020-12-01T13:06:57Z

On Tue, Dec 01, 2020 at 01:52:46PM +0100, Peter Zijlstra wrote:
> On Tue, Dec 01, 2020 at 12:56:27PM +0100, Sven Schnelle wrote:
> > Hi Peter,
> >
> > Peter Zijlstra <peterz@infradead.org> writes:
> >
> > > On Mon, Nov 30, 2020 at 01:00:03PM -0800, Guenter Roeck wrote:
> > >> On Fri, Nov 20, 2020 at 12:41:46PM +0100, Peter Zijlstra wrote:
> > >> > We call arch_cpu_idle() with RCU disabled, but then use
> > >> > local_irq_{en,dis}able(), which invokes tracing, which relies on RCU.
> > >> >
> > >> > Switch all arch_cpu_idle() implementations to use
> > >> > raw_local_irq_{en,dis}able() and carefully manage the
> > >> > lockdep,rcu,tracing state like we do in entry.
> > >> >
> > >> > (XXX: we really should change arch_cpu_idle() to not return with
> > >> > interrupts enabled)
> > >> >
> > >>
> > >> Has this patch been tested on s390 ? Reason for asking is that it causes
> > >> all my s390 emulations to crash. Reverting it fixes the problem.
> > >
> > > My understanding is that it changes the error on s390. Previously it
> > > would complain about the local_irq_enable() in arch_cpu_idle(), now it
> > > complains when taking an interrupt during idle.
> >
> > I looked into adding the required functionality for s390, but the code
> > we would need to add to entry.S is rather large - as you noted we would
> > have to duplicate large portions of irqentry_enter() into our code.
> > Given that s390 was fine before that patch, can you revert it and submit
> > it again during the next merge window?
>
> I'm not sure I understand how s390 was fine without it, let me consdier.
> Also, what's the status of ARM64, they do need this too.

For v5.10-rc6:

Build results:
total: 154 pass: 154 fail: 0
Qemu test results:
total: 426 pass: 421 fail: 5
Failed tests:
s390:defconfig:initrd
s390:defconfig:virtio-blk-ccw:rootfs
s390:defconfig:scsi[virtio-ccw]:rootfs
s390:defconfig:virtio-pci:rootfs
s390:defconfig:scsi[virtio-pci]:rootfs

At least with qemu all other tests/architectures are fine.
You can find the tested architectures at https://kerneltests.org/builders.

Guenter