Re: [PATCH v2] KVM: PPC: Book3S HV: Don't drop pending doorbell across L2 entry

Hi Vaibhav,

I have tested this v2 patch and it is still giving me the issue I reported,
so here is my analysis:

a) Without applying the patch :

1) Start the guest and run stress-ng as below for sometime
localhost:~ # stress-ng --cpu 4 --vm 2 --vm-bytes 1G --hdd 2 --hdd-bytes 1G
--sched other --timeout 3600000s
stress-ng: info:  [1464] setting to a 41 days, 16 hours, 0 secs run per
stressor
stress-ng: info:  [1464] dispatching hogs: 4 cpu, 2 vm, 2 hdd



2) Start the migration from H1 to H2:

ltc-lp7:~ # virsh migrate --live --domain sles16_anu
qemu+ssh://10.xx.xx.xx/system --verbose --undefinesource --persistent
--auto-converge --postcopy
(root@10.xx.xx.xx) Password:
Migration: [100.00 %]

3) Migration got completed but guest is not getting recovered from
continuous softlockups

[ 1336.003836][    C1] watchdog: BUG: soft lockup - CPU#1 stuck for 977s!
[htxd_monitor:1337]
[ 1336.006834][    C4] watchdog: BUG: soft lockup - CPU#4 stuck for 1002s!
[rcu_exp_par_gp_:19]
[ 1346.015839][    C0] BUG: workqueue lockup - pool cpus=1 node=0 flags=0x0
nice=0 stuck for 1090s!
[ 1346.016355][    C0] BUG: workqueue lockup - pool cpus=3 node=0 flags=0x0
nice=0 stuck for 1107s!
[ 1346.016874][    C0] BUG: workqueue lockup - pool cpus=7 node=0 flags=0x0
nice=0 stuck for 1093s!
[ 1356.007835][    C6] watchdog: BUG: soft lockup - CPU#6 stuck for 912s!
[systemd:1353]
[ 1356.008835][    C7] watchdog: BUG: soft lockup - CPU#7 stuck for 998s!
[systemd-journal:570]
[ 1360.003836][    C1] watchdog: BUG: soft lockup - CPU#1 stuck for 999s!
[htxd_monitor:1337]
[ 1360.006834][    C4] watchdog: BUG: soft lockup - CPU#4 stuck for 1024s!
[rcu_exp_par_gp_:19]
[ 1368.933835][    C4] rcu: INFO: rcu_preempt self-detected stall on CPU
[ 1368.933973][    C4] rcu:     4-....: (1129830 ticks this GP)
idle=afc4/1/0x4000000000000002 softirq=3694/428556 fqs=259639
[ 1368.934106][    C4] rcu:              hardirqs   softirqs  csw/system
[ 1368.934188][    C4] rcu:      number:        1     444039 0
[ 1368.934271][    C4] rcu:     cputime:        3          8 1096165   ==>
1110021(ms)
[ 1368.934373][    C4] rcu:     (t=1140022 jiffies g=6177 q=1684 ncpus=8)
[ 1376.224839][    C0] BUG: workqueue lockup - pool cpus=1 node=0 flags=0x0
nice=0 stuck for 1120s!
[ 1376.225307][    C0] BUG: workqueue lockup - pool cpus=3 node=0 flags=0x0
nice=0 stuck for 1138s!
[ 1376.225428][    C0] BUG: workqueue lockup - pool cpus=5 node=0 flags=0x0
nice=0 stuck for 715s!
[ 1376.225548][    C0] BUG: workqueue lockup - pool cpus=6 node=0 flags=0x0
nice=0 stuck for 1027s!
[ 1376.225667][    C0] BUG: workqueue lockup - pool cpus=7 node=0 flags=0x0
nice=0 stuck for 1123s!
[ 1444.006835][    C4] watchdog: BUG: soft lockup - CPU#4 stuck for 1100s!
[rcu_exp_par_gp_:19]


b) Even after applying the patch also it is giving same softlockup issue as
mentioned above:
Though I have enough vcpus and memory on the guest (16 vcpus , 13Gi of
memory)  and ample amount of memory and cpus
present on host still these softlockups are happening after applying the
patch too. I tried reducing stress also on the guest
but still this issue is seen.

stress-ng --cpu 4 --vm 2 --vm-bytes 1G --hdd 2 --hdd-bytes 1G --sched other
--timeout 3600000s

If you are planning to send next version of this patch,
Please do add my reported-by:
Reported-by: Anushree Mathur <redacted>

Thanks for testing this Anushree. Upon further debugging, I found that
this issue is likely due to a bug in QEMU, for which I've sent a fix[1].

@maddy: Please don't pull in this patch for now, will ping here if this
is needed.

[1] : lore.kernel.org/qemu-devel/20260824070353.40016-1-gautam@linux.ibm.com/

Thanks,
Gautam