Virtualization - Sep 2022 - [PATCH v3 6/6] freezer,sched: Rewrite core freezer logic

On Mon, Sep 26, 2022 at 03:23:10PM +0200, Christian Borntraeger
wrote:
> Am 26.09.22 um 14:55 schrieb Peter Zijlstra:
> 
> > Could you please test with something like the below on? I can boot
that
> > with KVM, but obviously I didn't suffer any weirdness to begin
with :/
> > 
> > ---
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 4e6a6417211f..ef9ccfc3a8c0 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -4051,6 +4051,8 @@ try_to_wake_up(struct task_struct *p, unsigned
int state, int wake_flags)
> >   	unsigned long flags;
> >   	int cpu, success = 0;
> > +	WARN_ON_ONCE(state & TASK_FREEZABLE);
> > +
> >   	preempt_disable();
> >   	if (p == current) {
> >   		/*
> 
> Does not seem to trigger.
Moo -- quite the puzzle this :/ I'll go stare at it more then.

Am 26.09.22 um 15:37 schrieb Peter Zijlstra:
> On Mon, Sep 26, 2022 at 03:23:10PM +0200, Christian Borntraeger wrote:
>> Am 26.09.22 um 14:55 schrieb Peter Zijlstra:
>>
>>> Could you please test with something like the below on? I can boot
that
>>> with KVM, but obviously I didn't suffer any weirdness to begin
with :/
>>>
>>> ---
>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>>> index 4e6a6417211f..ef9ccfc3a8c0 100644
>>> --- a/kernel/sched/core.c
>>> +++ b/kernel/sched/core.c
>>> @@ -4051,6 +4051,8 @@ try_to_wake_up(struct task_struct *p,
unsigned int state, int wake_flags)
>>>    	unsigned long flags;
>>>    	int cpu, success = 0;
>>> +	WARN_ON_ONCE(state & TASK_FREEZABLE);
>>> +
>>>    	preempt_disable();
>>>    	if (p == current) {
>>>    		/*
>>
>> Does not seem to trigger.
> 
> Moo -- quite the puzzle this :/ I'll go stare at it more then.
In the end this is about the end of the sshd process (shutting it down).
I can also trigger the problem by sending a SIGTERM so its not about
the shutdown itself.
Pofiling the guest I see scheduler functions like sched_clock, pick_next_entity,
update_min_vruntime and so on with 100% system time.

Am 26.09.22 um 15:37 schrieb Peter Zijlstra:
> On Mon, Sep 26, 2022 at 03:23:10PM +0200, Christian Borntraeger wrote:
>> Am 26.09.22 um 14:55 schrieb Peter Zijlstra:
>>
>>> Could you please test with something like the below on? I can boot
that
>>> with KVM, but obviously I didn't suffer any weirdness to begin
with :/
>>>
>>> ---
>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>>> index 4e6a6417211f..ef9ccfc3a8c0 100644
>>> --- a/kernel/sched/core.c
>>> +++ b/kernel/sched/core.c
>>> @@ -4051,6 +4051,8 @@ try_to_wake_up(struct task_struct *p,
unsigned int state, int wake_flags)
>>>    	unsigned long flags;
>>>    	int cpu, success = 0;
>>> +	WARN_ON_ONCE(state & TASK_FREEZABLE);
>>> +
>>>    	preempt_disable();
>>>    	if (p == current) {
>>>    		/*
>>
>> Does not seem to trigger.
> 
> Moo -- quite the puzzle this :/ I'll go stare at it more then.
Hmm,

#define ___wait_is_interruptible(state)                                        
\
         (!__builtin_constant_p(state) ||                                       
\
                 state == TASK_INTERRUPTIBLE || state == TASK_KILLABLE)         
\

That would not trigger when state is also TASK_FREEZABLE, no?