Linux kernel: powerpc: KVM guest can trigger host crash on Power8

[John Paul Adrian Glaubitz]

Hi Michael!

On 11/1/21 08:37, John Paul Adrian Glaubitz wrote:
> I made another experiment and upgraded the host to 5.15-rc7 which contains your
> fixes and made the guests build gcc-10. Interestingly, this time, the gcc-10
> build crashed the guest but didn't manage to crash the host. I will update the
> guest to 5.15-rc7 now as well and see how that goes.

OK, so I'm definitely able to crash the 5.15 kernel as well:

[57031.404944] watchdog: BUG: soft lockup - CPU#24 stuck for 14957s! [migration/24:14]
[57035.420898] watchdog: BUG: soft lockup - CPU#48 stuck for 14961s! [CPU 17/KVM:1815]
[57047.456761] watchdog: BUG: soft lockup - CPU#152 stuck for 14841s! [CPU 13/KVM:1811]
[57055.404670] watchdog: BUG: soft lockup - CPU#24 stuck for 14979s! [migration/24:14]
[57059.420624] watchdog: BUG: soft lockup - CPU#48 stuck for 14983s! [CPU 17/KVM:1815]
[57064.064573] rcu: INFO: rcu_sched self-detected stall on CPU
[57064.064584] rcu:     48-....: (3338577 ticks this GP) idle=9f3/1/0x4000000000000002 softirq=77540/77540 fqs=15421 
[57064.064598] rcu: rcu_sched kthread timer wakeup didn't happen for 3988041 jiffies! g125265 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x200
[57064.064606] rcu:     Possible timer handling issue on cpu=136 timer-softirq=313650
[57064.064611] rcu: rcu_sched kthread starved for 3988042 jiffies! g125265 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x200 ->cpu=136
[57064.064618] rcu:     Unless rcu_sched kthread gets sufficient CPU time, OOM is now expected behavior.
[57064.064624] rcu: RCU grace-period kthread stack dump:
[57064.064665] rcu: Stack dump where RCU GP kthread last ran:
[57071.456487] watchdog: BUG: soft lockup - CPU#152 stuck for 14863s! [CPU 13/KVM:1811]
[57079.404396] watchdog: BUG: soft lockup - CPU#24 stuck for 15002s! [migration/24:14]

And the gcc-10 testsuite is able to trigger the crash very reliably.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz at debian.org
`. `'   Freie Universitaet Berlin - glaubitz at physik.fu-berlin.de
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