Excerpts from Michal Suchánek's message of November 3, 2021 1:48 am: > 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 Hey Michal, great thanks for testing. Sorry I couldn't fix it, but a good result in the end. Thanks, Nick