Re: [PATCH v2 0/7] kvm: fix latent guest entry/exit bugs

[Christian Borntraeger <borntraeger@linux.ibm.com>]

Am 20.01.22 um 12:57 schrieb Mark Rutland:
> On Wed, Jan 19, 2022 at 08:30:17PM +0100, Christian Borntraeger wrote:
>>
>>
>> Am 19.01.22 um 20:22 schrieb Mark Rutland:
>>> On Wed, Jan 19, 2022 at 07:25:20PM +0100, Christian Borntraeger wrote:
>>>> Am 19.01.22 um 11:58 schrieb Mark Rutland:
>>>>
>>>>
>>>> CCing new emails for Anup and Atish so that they are aware of this thread.
>>>
>>> Ah; whoops. I'd meant to fix the Ccs on the patches.
>>>
>>> Thanks!
>>>
>>> [...]
>>>
>>>> I just gave this a spin on s390 with debugging on and I got the following:
>>>>
>>>> [  457.151295] ------------[ cut here ]------------
>>>> [  457.151311] WARNING: CPU: 14 PID: 0 at kernel/rcu/tree.c:613 rcu_eqs_enter.constprop.0+0xf8/0x118
>>>
>>> Hmm, so IIUC that's:
>>>
>>> 	WARN_ON_ONCE(rdp->dynticks_nmi_nesting != DYNTICK_IRQ_NONIDLE);
>>>
>>> ... and we're clearly in the idle thread here.
>>>
>>> I wonder, is the s390 guest entry/exit *preemptible* ?
>>
>> Looks like debug_defconfig is indeed using preemption:
>>
>> CONFIG_PREEMPT_BUILD=y
>> # CONFIG_PREEMPT_NONE is not set
>> # CONFIG_PREEMPT_VOLUNTARY is not set
>> CONFIG_PREEMPT=y
>> CONFIG_PREEMPT_COUNT=y
>> CONFIG_PREEMPTION=y
>> CONFIG_PREEMPT_RCU=y
>> CONFIG_PREEMPT_NOTIFIERS=y
>> CONFIG_DEBUG_PREEMPT=y
>> CONFIG_PREEMPTIRQ_TRACEPOINTS=y
>> CONFIG_TRACE_PREEMPT_TOGGLE=y
>> CONFIG_PREEMPT_TRACER=y
>> # CONFIG_PREEMPTIRQ_DELAY_TEST is not set
> 
> Thanks for confirming!
> 
> Could you try with CONFIG_PROVE_RCU=y ? That can't be selected directly, but
> selecting PROVE_LOCKING=y will enable it.

PROVE_LOCKING was enabled in my runs as well as PROVE_RCU.