On Thu, Jan 14, 2021 at 11:08:03PM +1000, Nicholas Piggin wrote:
> Excerpts from Michal Suchánek's message of January 14, 2021 10:40 pm:
> > On Mon, Oct 19, 2020 at 02:50:51PM +1000, Nicholas Piggin wrote:
> >> Excerpts from Nicholas Piggin's message of October 19, 2020 11:00 am:
> >> > Excerpts from Michal Suchánek's message of October 17, 2020 6:14 am:
> >> >> On Mon, Sep 07, 2020 at 11:13:47PM +1000, Nicholas Piggin wrote:
> >> >>> Excerpts from Michael Ellerman's message of August 31, 2020 8:50 pm:
> >> >>> > Michal Suchánek <msuchanek@xxxxxxx> writes:
> >> >>> >> On Mon, Aug 31, 2020 at 11:14:18AM +1000, Nicholas Piggin wrote:
> >> >>> >>> Excerpts from Michal Suchánek's message of August 31, 2020 6:11 am:
> >> >>> >>> > Hello,
> >> >>> >>> >
> >> >>> >>> > on POWER8 KVM hosts lock up since commit 10d91611f426 ("powerpc/64s:
> >> >>> >>> > Reimplement book3s idle code in C").
> >> >>> >>> >
> >> >>> >>> > The symptom is host locking up completely after some hours of KVM
> >> >>> >>> > workload with messages like
> >> >>> >>> >
> >> >>> >>> > 2020-08-30T10:51:31+00:00 obs-power8-01 kernel: KVM: couldn't grab cpu 47
> >> >>> >>> > 2020-08-30T10:51:31+00:00 obs-power8-01 kernel: KVM: couldn't grab cpu 71
> >> >>> >>> > 2020-08-30T10:51:31+00:00 obs-power8-01 kernel: KVM: couldn't grab cpu 47
> >> >>> >>> > 2020-08-30T10:51:31+00:00 obs-power8-01 kernel: KVM: couldn't grab cpu 71
> >> >>> >>> > 2020-08-30T10:51:31+00:00 obs-power8-01 kernel: KVM: couldn't grab cpu 47
> >> >>> >>> >
> >> >>> >>> > printed before the host locks up.
> >> >>> >>> >
> >> >>> >>> > The machines run sandboxed builds which is a mixed workload resulting in
> >> >>> >>> > IO/single core/mutiple core load over time and there are periods of no
> >> >>> >>> > activity and no VMS runnig as well. The VMs are shortlived so VM
> >> >>> >>> > setup/terdown is somewhat excercised as well.
> >> >>> >>> >
> >> >>> >>> > POWER9 with the new guest entry fast path does not seem to be affected.
> >> >>> >>> >
> >> >>> >>> > Reverted the patch and the followup idle fixes on top of 5.2.14 and
> >> >>> >>> > re-applied commit a3f3072db6ca ("powerpc/powernv/idle: Restore IAMR
> >> >>> >>> > after idle") which gives same idle code as 5.1.16 and the kernel seems
> >> >>> >>> > stable.
> >> >>> >>> >
> >> >>> >>> > Config is attached.
> >> >>> >>> >
> >> >>> >>> > I cannot easily revert this commit, especially if I want to use the same
> >> >>> >>> > kernel on POWER8 and POWER9 - many of the POWER9 fixes are applicable
> >> >>> >>> > only to the new idle code.
> >> >>> >>> >
> >> >>> >>> > Any idea what can be the problem?
> >> >>> >>>
> >> >>> >>> So hwthread_state is never getting back to to HWTHREAD_IN_IDLE on
> >> >>> >>> those threads. I wonder what they are doing. POWER8 doesn't have a good
> >> >>> >>> NMI IPI and I don't know if it supports pdbg dumping registers from the
> >> >>> >>> BMC unfortunately.
> >> >>> >>
> >> >>> >> It may be possible to set up fadump with a later kernel version that
> >> >>> >> supports it on powernv and dump the whole kernel.
> >> >>> >
> >> >>> > Your firmware won't support it AFAIK.
> >> >>> >
> >> >>> > You could try kdump, but if we have CPUs stuck in KVM then there's a
> >> >>> > good chance it won't work :/
> >> >>>
> >> >>> I haven't had any luck yet reproducing this still. Testing with sub
> >> >>> cores of various different combinations, etc. I'll keep trying though.
> >> >>
> >> >> Hello,
> >> >>
> >> >> I tried running some KVM guests to simulate the workload and what I get
> >> >> is guests failing to start with a rcu stall. Tried both 5.3 and 5.9
> >> >> kernel and qemu 4.2.1 and 5.1.0
> >> >>
> >> >> To start some guests I run
> >> >>
> >> >> for i in $(seq 0 9) ; do /opt/qemu/bin/qemu-system-ppc64 -m 2048 -accel kvm -smp 8 -kernel /boot/vmlinux -initrd /boot/initrd -nodefaults -nographic -serial mon:telnet::444$i,server,wait & done
> >> >>
> >> >> To simulate some workload I run
> >> >>
> >> >> xz -zc9T0 < /dev/zero > /dev/null &
> >> >> while true; do
> >> >> killall -STOP xz; sleep 1; killall -CONT xz; sleep 1;
> >> >> done &
> >> >>
> >> >> on the host and add a job that executes this to the ramdisk. However, most
> >> >> guests never get to the point where the job is executed.
> >> >>
> >> >> Any idea what might be the problem?
> >> >
> >> > I would say try without pv queued spin locks (but if the same thing is
> >> > happening with 5.3 then it must be something else I guess).
> >> >
> >> > I'll try to test a similar setup on a POWER8 here.
> >>
> >> Couldn't reproduce the guest hang, they seem to run fine even with
> >> queued spinlocks. Might have a different .config.
> >>
> >> I might have got a lockup in the host (although different symptoms than
> >> the original report). I'll look into that a bit further.
> >
> > Hello,
> >
> > any progress on this?
>
> No progress, I still wasn't able to reproduce, and it fell off the
> radar sorry.
>
> I expect hwthred_state must be getting corrupted somewhere or a
> secondary thread getting stuck but I couldn't see where. I try pick
> it up again thanks for the reminder.
Hello,
the fixes pointed out in
https://lore.kernel.org/linuxppc-dev/87pmrtbbdt.fsf@xxxxxxxxxxxxxxxxxx/T/#u
resolve the problem.
Thanks
Michal
