On Fri, Sep 04, 2026 at 02:34:21PM +0530, Shrikanth Hegde wrote:
>
>
> On 9/4/26 1:05 PM, Michal Suchánek wrote:
> > On Thu, Sep 03, 2026 at 10:52:59PM +0530, Shrikanth Hegde wrote:
> > >
> > > > > If possible run against current upstream and share the results.
> > > >
> > > > https://github.com/openSUSE/kernel-source/blob/6824496d1801f73def615dca8794202eeb7b0d86/config/ppc64le/default
> > > >
> > > > [ 472.091531][ T6181] Kernel panic - not syncing: stack-protector:
> > > > Kernel stack is corrupted in: kvmhv_run_single_vcpu+0x19d4/0x1b50
> > > > [kvm_hv]
> > > > [ 472.091598][ T6181] CPU: 29 UID: 107 PID: 6181 Comm: CPU 112/KVM Not
> > > > tainted 7.2.2-5.g6824496-default #1 PREEMPT(full) openSUSE Tumbleweed
> > > > (unreleased) 61871a5f06863b4006f5ef27cd9f18e8a7a2edad
> > > > [ 472.091612][ T6181] Hardware name: IBM,9824-42A Power11
> > > > (architected) 0x820200 0xf000007 of:IBM,FW1110.20 (OB1110_130) hv:phyp
> > > > pSeries
> > > > [ 472.091624][ T6181] Call Trace:
> > > > [ 472.091630][ T6181] [c00000000fdfb680] [c00000000134ce90]
> > > > dump_stack_lvl+0x84/0xc0 (unreliable)
> > > > [ 472.091653][ T6181] [c00000000fdfb6b0] [c00000000022e7c8]
> > > > vpanic+0x324/0x5e4
> > > > [ 472.091666][ T6181] [c00000000fdfb760] [c00000000022eac4]
> > > > do_panic_on_target_cpu+0x0/0x2c
> > > > [ 472.091677][ T6181] [c00000000fdfb780] [c0000000013c1ff8]
> > > > __stack_chk_fail+0x48/0x60
> > > > [ 472.091689][ T6181] [c00000000fdfb7f0] [c00800001aae219c]
> > > > kvmhv_run_single_vcpu+0x19d4/0x1b50 [kvm_hv]
> > > > [ 472.091712][ T6181] [c00000000fdfb940] [c00800001aae24b4]
> > > > kvmppc_vcpu_run_hv+0x19c/0x12f0 [kvm_hv]
> > > > [ 472.091732][ T6181] [c00000000fdfba10] [c00800001aeeed18]
> > > > kvmppc_vcpu_run+0x30/0x48 [kvm]
> > > > [ 472.091779][ T6181] [c00000000fdfba30] [c00800001aee9ef4]
> > > > kvm_arch_vcpu_ioctl_run+0x35c/0x4a0 [kvm]
> > > > [ 472.091813][ T6181] [c00000000fdfbac0] [c00800001aedaac4]
> > > > kvm_vcpu_ioctl+0x1ac/0xad8 [kvm]
> > > > [ 472.091844][ T6181] [c00000000fdfbca0] [c0000000007f1244]
> > > > sys_ioctl+0x374/0x1060
> > > > [ 472.091857][ T6181] [c00000000fdfbdb0] [c00000000002f7f8]
> > > > system_call_exception+0x188/0x430
> > > > [ 472.091871][ T6181] [c00000000fdfbe50] [c00000000000cfdc]
> > > > system_call_vectored_common+0x15c/0x2ec
> > > > [ 472.091886][ T6181] ---- interrupt: 3000 at 0x7fffb5565fac
> > > > [ 472.091896][ T6181] NIP: 00007fffb5565fac LR: 00007fffb5565fac CTR:
> > > > 0000000000000000
> > > > [ 472.091904][ T6181] REGS: c00000000fdfbe80 TRAP: 3000 Not tainted
> > > > (7.2.2-5.g6824496-default)
> > > > [ 472.091911][ T6181] MSR: 800000000280f033
> > > > <SF,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE> CR: 42044402 XER: 00000000
> > > > [ 472.091938][ T6181] IRQMASK: 0
> > > > [ 472.091938][ T6181] GPR00: 0000000000000036 00007fbfa77ed7a0
> > > > 00007fffb5677100 00000000000000fa
> > > > [ 472.091938][ T6181] GPR04: 000000002000ae80 0000000000000000
> > > > 0000000000000000 0000000000000000
> > > > [ 472.091938][ T6181] GPR08: 00000000000000fa 0000000000000000
> > > > 0000000000000000 0000000000000000
> > > > [ 472.091938][ T6181] GPR12: 0000000000000000 00007fbfa77f5ec0
> > > > 000000014676f000 00007fbfa77ee7c0
> > > > [ 472.091938][ T6181] GPR16: 000000014674e8d0 00007fbfa77eeec0
> > > > 00007fbfa77eeec0 fffffffffffffff7
> > > > [ 472.091938][ T6181] GPR20: 00007fffb71210d0 0000000000000001
> > > > 00007fbfa77eeec0 0000000000000000
> > > > [ 472.091938][ T6181] GPR24: 00007fbfa77ed8e8 0000000105971428
> > > > 000000002000ae80 0000000105f77a70
> > > > [ 472.091938][ T6181] GPR28: 0000000000000000 0000000000000000
> > > > 000000002000ae80 000000014674f000
> > > > [ 472.092020][ T6181] NIP [00007fffb5565fac] 0x7fffb5565fac
> > > > [ 472.092027][ T6181] LR [00007fffb5565fac] 0x7fffb5565fac
> > > > [ 472.092033][ T6181] ---- interrupt: 3000
> > > > [ 472.098256][ T6181] pstore: backend (nvram) writing error (-1)
> > > >
> > > > This is the host, cannot run the kernel as guest because it fails to
> > > > boot most
> > > > of the time inside KVM.
> > > >
> > > > >
> > > > > > Nonethless, there are quite a few platforms. Originally no
> > > > > > preemption
> > > > > > was the only option, and that's the reason why many people run that.
> > > > > > It's the conservative, known working option. And that's the reason
> > > > > > a lot
> > > > > > of platfrom code does not get tested with more aggressive preemtion
> > > > > > models, and never gets fixed to work with them.
> > > > > >
> > > > >
> > > > > Full preemption has been there for many years!.
> > > >
> > > > Possible for years, forced only recently.
> > > >
> > > > > Lazy is not that aggressive compared to that.
> > > > >
> > > > > > Simply disabling the no preemtion option does not make the platform
> > > > > > code
> > > > > > ready.
> > > > > >
> > > > >
> > > > > Let's understand your crash case. Let's see where it is going wrong.
> > > > > I am suspecting
> > > > > it is some wrong usage of preemption api rather than arch can't
> > > > > support preemption.
> > > >
> > > > Very likely some wrong use of the preemption API by the arch code, or no
> > > > use where it should have been used. It did not matter so long as people
> > > > could run their no preempt configs and ignore the problem.
> > > >
> > > > Thanks
> > >
> > >
> > > Friendly LLM analysis says preemption is enabled too early and before
> > > completing kvmppc_handle_exit_hv() / kvmppc_handle_nested_exit()
> > >
> > > Below is ONLY a speculation and completely UNTESTED.
> > > Maybe worth a try.
> >
> > The patch is munged by the e-mail client, and it causes immediate
> > voluntary preemprion in rcu critical section and hard lockup on starting
> > a KVM VM.
> >
> > Also it would be sort of bad news if it worked because that would be
> > specific to book3s KVM HV and would not help with the KVM HV from the
> > original report which likely is not book3s, nor with KVM PR.
> >
>
> Thanks for trying. We will try a local repro and look into it why stack is
> getting corrupted.
There is also stack corruption when idling. At this point the machine is
stuck half-dead and would not go through with the panic, it requires
dump from the hyprvisor side to capture this.
Thanks
Michal
[542489.550547] [ T0] Kernel panic - not syncing: stack-protector: Kernel
stack is corrupted in: __sprint_symbol+0x1e4/0x1f0
[542489.557809] [ T0] ------------[ cut here ]------------
[542489.557814] [ T0] Voluntary context switch within RCU read-side
critical section!
[542489.557822] [ T0] WARNING: [] kernel/rcu/tree_plugin.h:332 at
rcu_note_context_switch+0x6a0/0x7b0, CPU#59: swapper/59/0
[542489.557837] [ T0] Modules linked in: vhost_net vhost vhost_iotlb tap
rpadlpar_io rpaphp kvm_hv kvm mptcp_diag xsk_diag tcp_diag udp_diag raw_diag
inet_diag unix_diag af_packet_diag netlink_diag xt_conntrack xt_MASQUERADE
xfrm_user xt_set ip_set xt_addrtype nft_compat nf_conntrack_netbios_ns
nf_conntrack_broadcast nft_masq nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib
nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct bonding tls
nft_chain_nat nf_nat nf_conntrack tun nf_defrag_ipv6 nf_defrag_ipv4 rfkill
af_packet binfmt_misc xfs aes_gcm_p10_crypto crypto_simd ibmveth cryptd xts
vmx_crypto rtc_generic fuse nvme_fabrics ip_tables x_tables ibmvscsi
scsi_transport_srp sd_mod scsi_dh_emc scsi_dh_rdac scsi_dh_alua sg scsi_mod
scsi_common nvme nvme_core nvme_keyring nvme_auth pseries_wdt btrfs xor
libblake2b raid6_pq dm_mirror dm_region_hash dm_log dm_mod br_netfilter bridge
stp llc nf_tables
[542489.557944] [ T0] CPU: 59 UID: 0 PID: 0 Comm: swapper/59 Tainted: G
D W 7.2.2-5.g6824496-default #1 PREEMPT(full) openSUSE Tumbleweed
(unreleased) 61871a5f06863b4006f5ef27cd9f18e8a7a2edad
[542489.557957] [ T0] Tainted: [D]=DIE, [W]=WARN
[542489.557961] [ T0] Hardware name: IBM,9824-42A Power11 (architected)
0x820200 0xf000007 of:IBM,FW1110.20 (OB1110_130) hv:phyp pSeries
[542489.557967] [ T0] NIP: c00000000035d700 LR: c00000000035d6fc CTR:
0000000000000000
[542489.557974] [ T0] REGS: c000001de047f990 TRAP: 0700 Tainted: G
D W (7.2.2-5.g6824496-default)
[542489.557980] [ T0] MSR: 800000000282b033
<SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 44002284 XER: 0000000e
[542489.557999] [ T0] CFAR: c00000000022d7a8 IRQMASK: 1
GPR00: c00000000035d6fc c000001de047fc30
c00000000205ad00 000000000000003f
GPR04: 3ffffffffffc02ef c000001de047f950
c000001de047f910 0000003ff0e20000
GPR08: 0000000000000027 0000000000000001
c000001de0191300 0000000044002284
GPR12: c000003ff1614890 c000003fffff9f00
0000000000000000 000000002eef9860
GPR16: 0000000000000000 c000003ff40dcc80
0000003ff0e20000 c000000000058010
GPR20: c000000000058160 c0000000032bcc80
c0000000032bcc80 c000000000057f80
GPR24: ffffffffffffffff 000000000000003b
c000001de0191300 c000000003bea6e0
GPR28: c000000000058010 ffffffffffffffff
0000000000000000 c000003ff40de100
[542489.558066] [ T0] NIP [c00000000035d700]
rcu_note_context_switch+0x6a0/0x7b0
[542489.558072] [ T0] LR [c00000000035d6fc]
rcu_note_context_switch+0x69c/0x7b0
[542489.558078] [ T0] Call Trace:
[542489.558082] [ T0] [c000001de047fc30] [c00000000035d6fc]
rcu_note_context_switch+0x69c/0x7b0 (unreliable)
[542489.558092] [ T0] [c000001de047fcd0] [c0000000013c4fc0]
__schedule+0xf0/0x1d10
[542489.558108] [ T0] [c000001de047fe20] [c0000000013c6eb0]
schedule_idle+0x30/0x60
[542489.558121] [ T0] [c000001de047fe40] [c0000000002caed8]
do_idle+0x258/0x470
[542489.558133] [ T0] [c000001de047feb0] [c0000000002cb3b4]
cpu_startup_entry+0x54/0x60
[542489.558145] [ T0] [c000001de047fee0] [c00000000005a720]
start_secondary+0x860/0xd70
[542489.558154] [ T0] [c000001de047ffe0] [c00000000000e158]
start_secondary_prolog+0x10/0x14
[542489.558162] [ T0] Code: f8c900a8 4bfffe6c 60000000 60420000 3c62ff87
39200001 f9410068 3d4201b2 386329d8 992aa087 4becff91 60000000 <0fe00000>
e9410068 4bfff9c4 60420000
[542489.558184] [ T0] ---[ end trace 0000000000000000 ]---
[542521.228724] [ C59] watchdog: CPU 59 Hard LOCKUP
[542521.228726] [ C59] watchdog: CPU 59 TB:3697937465165330, last heartbeat
TB:3697921085812082 (31990ms ago)
[542521.228728] [ C59] Modules linked in: vhost_net vhost vhost_iotlb tap
rpadlpar_io rpaphp kvm_hv kvm mptcp_diag xsk_diag tcp_diag udp_diag raw_diag
inet_diag unix_diag af_packet_diag netlink_diag xt_conntrack xt_MASQUERADE
xfrm_user xt_set ip_set xt_addrtype nft_compat nf_conntrack_netbios_ns
nf_conntrack_broadcast nft_masq nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib
nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct bonding tls
nft_chain_nat nf_nat nf_conntrack tun nf_defrag_ipv6 nf_defrag_ipv4 rfkill
af_packet binfmt_misc xfs aes_gcm_p10_crypto crypto_simd ibmveth cryptd xts
vmx_crypto rtc_generic fuse nvme_fabrics ip_tables x_tables ibmvscsi
scsi_transport_srp sd_mod scsi_dh_emc scsi_dh_rdac scsi_dh_alua sg scsi_mod
scsi_common nvme nvme_core nvme_keyring nvme_auth pseries_wdt btrfs xor
libblake2b raid6_pq dm_mirror dm_region_hash dm_log dm_mod br_netfilter bridge
stp llc nf_tables
[542521.228776] [ C59] CPU: 59 UID: 0 PID: 0 Comm: swapper/59 Tainted: G
D W 7.2.2-5.g6824496-default #1 PREEMPT(full) openSUSE Tumbleweed
(unreleased) 61871a5f06863b4006f5ef27cd9f18e8a7a2edad
[542521.228780] [ C59] Tainted: [D]=DIE, [W]=WARN
[542521.228781] [ C59] Hardware name: IBM,9824-42A Power11 (architected)
0x820200 0xf000007 of:IBM,FW1110.20 (OB1110_130) hv:phyp pSeries
[542521.228783] [ C59] NIP: c0000000013d2c94 LR: c0000000013d5330 CTR:
c000000003812be8
[542521.228785] [ C59] REGS: c000003ffed2bd60 TRAP: 0100 Tainted: G
D W (7.2.2-5.g6824496-default)
[542521.228788] [ C59] MSR: 8000000000081033 <SF,ME,IR,DR,RI,LE> CR:
42002282 XER: 2004000e
[542521.228794] [ C59] CFAR: 000000000000011c IRQMASK: 3
GPR00: c000000000260a58 c000003ffef2fb60
c00000000205ad00 c000001deaab3c00
GPR04: 00000000000001f8 0000000000000000
fffffffffffe0000 0000000000010000
GPR08: 0000000000000001 0000000000000001
000000001c82ef77 fffffffffffffffd
GPR12: c000000003812be0 c000003fffff9f00
0000000000000000 0000000000000000
GPR16: 0000000000000000 0000000000000000
0000000000000001 c000000003bc2b00
GPR20: c000003ff40c8de8 0000000000000001
c000003ff40c8da8 c000003ffef2fe08
GPR24: 0000000000000000 c000000003bea6e0
000000000000003b 0000003ff0e20000
GPR28: 0000000000780000 c0000000032bbe80
c000003ff40dbe80 c000001deaab3c00
[542521.228820] [ C59] NIP [c0000000013d2c94]
queued_spin_lock_slowpath+0x164/0x19a0
[542521.228824] [ C59] LR [c0000000013d5330] _raw_spin_lock+0x80/0xa0
[542521.228827] [ C59] Call Trace:
[542521.228827] [ C59] [c000003ffef2fb60] [0000000000001000] 0x1000
(unreliable)
[542521.228833] [ C59] [c000003ffef2fc60] [c000001de0191300]
0xc000001de0191300
[542521.228836] [ C59] [c000003ffef2fc80] [c000000000260a58]
__queue_work+0x2f8/0x740
[542521.228841] [ C59] [c000003ffef2fd50] [c00000000038ceac]
call_timer_fn+0x4c/0x260
[542521.228845] [ C59] [c000003ffef2fde0] [c00000000038d308]
__run_timers+0x248/0x410
[542521.228849] [ C59] [c000003ffef2fec0] [c00000000038d56c]
run_timer_softirq+0x9c/0x130
[542521.228852] [ C59] [c000003ffef2fef0] [c00000000023ab0c]
handle_softirqs+0x14c/0x4a0
[542521.228855] [ C59] [c000003ffef2ffe0] [c000000000018418]
do_softirq_own_stack+0x38/0x50
[542521.228860] [ C59] [c000001de047f910] [c00000000023a238]
__irq_exit_rcu+0x198/0x1c0
[542521.228862] [ C59] [c000001de047f940] [c000000000026acc]
timer_interrupt+0x1cc/0x4f0
[542521.228866] [ C59] [c000001de047f9b0] [c000000000009fdc]
decrementer_common_virt+0x28c/0x290
[542521.228871] [ C59] ---- interrupt: 900 at
plpar_hcall_norets_notrace+0x18/0x2c
[542521.228876] [ C59] NIP: c0000000001b7634 LR: c0000000013c4898 CTR:
0000000000000000
[542521.228877] [ C59] REGS: c000001de047f9e0 TRAP: 0900 Tainted: G
D W (7.2.2-5.g6824496-default)
[542521.228879] [ C59] MSR: 800000000280b033
<SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 22000282 XER: 2004000e
[542521.228886] [ C59] CFAR: 0000000000000000 IRQMASK: 0
GPR00: 0000000000000000 c000001de047fc80
c00000000205ad00 0000000000000000
GPR04: 0000000000000000 0000000000000039
0000000000000000 0000000000000000
GPR08: ffffffffffffff7f 0000000000000000
ffffffffffffffff 0000000000000000
GPR12: 0000000000000000 c000003fffff9f00
0000000000000000 000000002eef9860
GPR16: 0000000000000000 0000000000000001
0000000000000001 c000000000058010
GPR20: c000000000058160 0000000000000002
c000000000057fb0 c000000000057f80
GPR24: ffffffffffffffff 0001ed6431fbb852
0000000000000000 0000000000000001
GPR28: 0000000000000000 0000000000000000
c0000000032a1878 c0000000032a1870
[542521.228911] [ C59] NIP [c0000000001b7634]
plpar_hcall_norets_notrace+0x18/0x2c
[542521.228915] [ C59] LR [c0000000013c4898]
check_and_cede_processor+0x48/0x60
[542521.228918] [ C59] ---- interrupt: 900
[542521.228919] [ C59] [c000001de047fc80] [ffffffffffffffff]
0xffffffffffffffff (unreliable)
[542521.228922] [ C59] [c000001de047fce0] [c0000000013c4944]
dedicated_cede_loop+0x94/0x1a0
[542521.228926] [ C59] [c000001de047fd30] [c0000000013c3f00]
cpuidle_enter_state+0x300/0x748
[542521.228930] [ C59] [c000001de047fde0] [c000000000f5ff10]
cpuidle_enter+0x50/0x80
[542521.228935] [ C59] [c000001de047fe20] [c0000000002ba358]
call_cpuidle+0x48/0x90
[542521.228939] [ C59] [c000001de047fe40] [c0000000002caf5c]
do_idle+0x2dc/0x470
[542521.228942] [ C59] [c000001de047feb0] [c0000000002cb3b8]
cpu_startup_entry+0x58/0x60
[542521.228945] [ C59] [c000001de047fee0] [c00000000005a720]
start_secondary+0x860/0xd70
[542521.228948] [ C59] [c000001de047ffe0] [c00000000000e158]
start_secondary_prolog+0x10/0x14
[542521.228951] [ C59] Code: 41810e8c 39400000 39000000 3cc0fffe 60000000
813f0000 71290001 41820050 3ce00001 60000000 60420000 7c40003c <71090001>
394a0001 40820028 3d2201ba
[568119.679467] [ C59] pstore: dump skipped in NMI path because of
concurrent dump
