[PATCH 39/47] clocksource: hyper-v: Move CPUHP_AP_HYPERV_TIMER_STARTING post stop_machine()

[PATCH 39/47] clocksource: hyper-v: Move CPUHP_AP_HYPERV_TIMER_STARTING post stop_machine()

[Frederic Weisbecker]

Between CPUHP_TEARDOWN_CPU and CPUHP_AP_OFFLINE, stop_machine executes
all the teardown callbacks while stopping all CPUs in the system. This
doesn't mix-up well with running RT or isolated tasks.

In order to transition smoothly from global stop_machine to finer
grained synchronization between teardown callbacks and the other CPUs,
a new stop machine post function has been introduced to be executed
after the main one with IRQs still disabled while other CPUs can exit
stop_machine().

The teardown callback here simply performs timer and IRQ disablement,
both of which can run concurrently with other CPUs.

Move it to post stop_machine() accordingly.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 kernel/cpu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 93b8498e26c4..b49b67ef5ecb 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1275,7 +1275,7 @@ void clear_tasks_mm_cpumask(int cpu)
 static int take_cpu_down(void *_param)
 {
 	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
-	enum cpuhp_state target = max((int)st->target, CPUHP_AP_TI_GP_TIMER_STARTING);
+	enum cpuhp_state target = max((int)st->target, CPUHP_AP_HYPERV_TIMER_STARTING);
 	int err, cpu = smp_processor_id();
 
 	/* Ensure this CPU doesn't handle any more interrupts. */
@@ -1303,7 +1303,7 @@ static int take_cpu_down_post(void *_param)
 	enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
 	int cpu = smp_processor_id();
 
-	WARN_ON(st->state != CPUHP_AP_TI_GP_TIMER_STARTING);
+	WARN_ON(st->state != CPUHP_AP_HYPERV_TIMER_STARTING);
 	/*
 	 * Invoke the former CPU_DYING callbacks. DYING must not fail!
 	 */
-- 
2.53.0

Re: [PATCH 39/47] clocksource: hyper-v: Move CPUHP_AP_HYPERV_TIMER_STARTING post stop_machine()

[Naman Jain]

On 11/5/2026 10:00 PM, Frederic Weisbecker wrote:
> Between CPUHP_TEARDOWN_CPU and CPUHP_AP_OFFLINE, stop_machine executes
> all the teardown callbacks while stopping all CPUs in the system. This
> doesn't mix-up well with running RT or isolated tasks.
> 
> In order to transition smoothly from global stop_machine to finer
> grained synchronization between teardown callbacks and the other CPUs,
> a new stop machine post function has been introduced to be executed
> after the main one with IRQs still disabled while other CPUs can exit
> stop_machine().
> 
> The teardown callback here simply performs timer and IRQ disablement,
> both of which can run concurrently with other CPUs.
> 
> Move it to post stop_machine() accordingly.
> 
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> ---
>   kernel/cpu.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 93b8498e26c4..b49b67ef5ecb 100644

I am unable to correlate the commit message with the change and could 
not find the rest of the series on lore to get more context.


Regards,
Naman

> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1275,7 +1275,7 @@ void clear_tasks_mm_cpumask(int cpu)
>   static int take_cpu_down(void *_param)
>   {
>   	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
> -	enum cpuhp_state target = max((int)st->target, CPUHP_AP_TI_GP_TIMER_STARTING);
> +	enum cpuhp_state target = max((int)st->target, CPUHP_AP_HYPERV_TIMER_STARTING);
>   	int err, cpu = smp_processor_id();
>   
>   	/* Ensure this CPU doesn't handle any more interrupts. */
> @@ -1303,7 +1303,7 @@ static int take_cpu_down_post(void *_param)
>   	enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
>   	int cpu = smp_processor_id();
>   
> -	WARN_ON(st->state != CPUHP_AP_TI_GP_TIMER_STARTING);
> +	WARN_ON(st->state != CPUHP_AP_HYPERV_TIMER_STARTING);
>   	/*
>   	 * Invoke the former CPU_DYING callbacks. DYING must not fail!
>   	 */

Re: [PATCH 39/47] clocksource: hyper-v: Move CPUHP_AP_HYPERV_TIMER_STARTING post stop_machine()

[Frederic Weisbecker]

Le Fri, Nov 06, 2026 at 03:37:26PM +0530, Naman Jain a écrit :
> 
> 
> On 11/5/2026 10:00 PM, Frederic Weisbecker wrote:
> > Between CPUHP_TEARDOWN_CPU and CPUHP_AP_OFFLINE, stop_machine executes
> > all the teardown callbacks while stopping all CPUs in the system. This
> > doesn't mix-up well with running RT or isolated tasks.
> > 
> > In order to transition smoothly from global stop_machine to finer
> > grained synchronization between teardown callbacks and the other CPUs,
> > a new stop machine post function has been introduced to be executed
> > after the main one with IRQs still disabled while other CPUs can exit
> > stop_machine().
> > 
> > The teardown callback here simply performs timer and IRQ disablement,
> > both of which can run concurrently with other CPUs.
> > 
> > Move it to post stop_machine() accordingly.
> > 
> > Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> > ---
> >   kernel/cpu.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/cpu.c b/kernel/cpu.c
> > index 93b8498e26c4..b49b67ef5ecb 100644
> 
> I am unable to correlate the commit message with the change and could not
> find the rest of the series on lore to get more context.

Sorry about that. I couldn't CC everyone to the motherpatch so I tried
to bring as much context as I could to each individual follow-up's changelog.
Probably that wasn't enough.

So here is the cover letter that explains the whole intent:

https://lore.kernel.org/lkml/20261105163045.38862-1-frederic@kernel.org/

And the patch that does the initial infrastructure change to stop machine:

https://lore.kernel.org/lkml/20261105163045.38862-2-frederic@kernel.org/

Thanks.

-- 
Frederic Weisbecker
SUSE Labs