Re: [RFC 1/2] PM: Add suspend and hibernate notifications for after freeze

[Mario Limonciello <superm1@kernel.org>]

On 5/1/2025 4:17 PM, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@amd.com>
> 
> Suspend and hibernate notifications are available specifically when
> the sequence starts and finishes.  However there are no notifications
> during the process when tasks have been frozen.
> 
> Introduce two new events `PM_SUSPEND_POST_FREEZE` and
> `PM_HIBERNATE_POST_FREEZE` that drivers can subscribe to and take
> different actions specifically knowing userspace is frozen.
> 
> Suggested-by: Alex Deucher <alexander.deucher@amd.com>
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
>   Documentation/driver-api/pm/notifiers.rst | 19 ++++++++++++++++---
>   include/linux/suspend.h                   | 14 ++++++++------
>   kernel/power/hibernate.c                  |  9 +++++++--
>   kernel/power/suspend.c                    | 13 +++++++++----
>   4 files changed, 40 insertions(+), 15 deletions(-)
> 
> diff --git a/Documentation/driver-api/pm/notifiers.rst b/Documentation/driver-api/pm/notifiers.rst
> index 186435c43b77e..6a1912fbee214 100644
> --- a/Documentation/driver-api/pm/notifiers.rst
> +++ b/Documentation/driver-api/pm/notifiers.rst
> @@ -32,6 +32,18 @@ will be called upon the following events by the PM core:
>   	additional work is done between the notifiers and the invocation of PM
>   	callbacks for the "freeze" transition.
>   
> +``PM_HIBERNATION_POST_FREEZE``
> +	The system is going to hibernate and tasks have just been frozen.
> +
> +``PM_SUSPEND_PREPARE``
> +	The system is going to suspend, tasks will be frozen immediately.  This
> +	is different from ``PM_HIBERNATION_PREPARE`` above, because in this case
> +	additional work is done between the notifiers and the invocation of PM
> +	callbacks for the "freeze" transition.

I accidentally created this section ``PM_SUSPEND_PREPARE`` (there 
already is one for PM_SUSPEND_PREPARE that is totally fine).

If conceptually the rest of the patch makes sense I will drop this section.

> +
> +``PM_SUSPEND_POST_FREEZE``
> +	The system is going to suspend and tasks have just been frozen.

Looking again, I think this is better put between (the correct) 
PM_SUSPEND_PREPARE and PM_POST_SUSPEND.

If conceptually the rest of the patch makes sense I will move it to that 
section.

> +
>   ``PM_POST_HIBERNATION``
>   	The system memory state has been restored from a hibernation image or an
>   	error occurred during hibernation.  Device restore callbacks have been
> @@ -54,9 +66,10 @@ will be called upon the following events by the PM core:
>   	resume callbacks have been executed and tasks have been thawed.
>   
>   It is generally assumed that whatever the notifiers do for
> -``PM_HIBERNATION_PREPARE``, should be undone for ``PM_POST_HIBERNATION``.
> -Analogously, operations carried out for ``PM_SUSPEND_PREPARE`` should be
> -reversed for ``PM_POST_SUSPEND``.
> +``PM_HIBERNATION_PREPARE`` and ``PM_HIBERNATION_POST_FREEZE``, should be undone
> +for ``PM_POST_HIBERNATION``.
> +Analogously, operations carried out for ``PM_SUSPEND_PREPARE`` and ``PM_SUSPEND_POST_FREEZE``
> +should be reversed for ``PM_POST_SUSPEND``.
>   
>   Moreover, if one of the notifiers fails for the ``PM_HIBERNATION_PREPARE`` or
>   ``PM_SUSPEND_PREPARE`` event, the notifiers that have already succeeded for that
> diff --git a/include/linux/suspend.h b/include/linux/suspend.h
> index da6ebca3ff774..704e6579b0df6 100644
> --- a/include/linux/suspend.h
> +++ b/include/linux/suspend.h
> @@ -422,12 +422,14 @@ static inline int is_hibernate_resume_dev(dev_t dev) { return 0; }
>   #endif
>   
>   /* Hibernation and suspend events */
> -#define PM_HIBERNATION_PREPARE	0x0001 /* Going to hibernate */
> -#define PM_POST_HIBERNATION	0x0002 /* Hibernation finished */
> -#define PM_SUSPEND_PREPARE	0x0003 /* Going to suspend the system */
> -#define PM_POST_SUSPEND		0x0004 /* Suspend finished */
> -#define PM_RESTORE_PREPARE	0x0005 /* Going to restore a saved image */
> -#define PM_POST_RESTORE		0x0006 /* Restore failed */
> +#define PM_HIBERNATION_PREPARE		0x0001 /* Going to hibernate */
> +#define PM_HIBERNATION_POST_FREEZE	0x0002 /* Prepared for hibernation and tasks have been frozen */
> +#define PM_POST_HIBERNATION		0x0003 /* Hibernation finished */
> +#define PM_SUSPEND_PREPARE		0x0004 /* Going to suspend the system */
> +#define PM_SUSPEND_POST_FREEZE		0x0005 /* Prepared and tasks have been frozen */
> +#define PM_POST_SUSPEND			0x0006 /* Suspend finished */
> +#define PM_RESTORE_PREPARE		0x0007 /* Going to restore a saved image */
> +#define PM_POST_RESTORE			0x0008 /* Restore failed */
>   
>   extern struct mutex system_transition_mutex;
>   
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index f0db9d1896e80..f896056ad2e5d 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -783,11 +783,15 @@ int hibernate(void)
>   	if (error)
>   		goto Exit;
>   
> +	error = pm_notifier_call_chain_robust(PM_HIBERNATION_POST_FREEZE, PM_POST_HIBERNATION);
> +	if (error)
> +		goto Thaw;
> +
>   	lock_device_hotplug();
>   	/* Allocate memory management structures */
>   	error = create_basic_memory_bitmaps();
>   	if (error)
> -		goto Thaw;
> +		goto Unlock_hotplug;
>   
>   	error = hibernation_snapshot(hibernation_mode == HIBERNATION_PLATFORM);
>   	if (error || freezer_test_done)
> @@ -833,8 +837,9 @@ int hibernate(void)
>   
>    Free_bitmaps:
>   	free_basic_memory_bitmaps();
> - Thaw:
> + Unlock_hotplug:
>   	unlock_device_hotplug();
> + Thaw:
>   	if (snapshot_test) {
>   		pm_pr_dbg("Checking hibernation image\n");
>   		error = swsusp_check(false);
> diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
> index 8eaec4ab121d4..bc6654e8cdc80 100644
> --- a/kernel/power/suspend.c
> +++ b/kernel/power/suspend.c
> @@ -377,13 +377,18 @@ static int suspend_prepare(suspend_state_t state)
>   	trace_suspend_resume(TPS("freeze_processes"), 0, true);
>   	error = suspend_freeze_processes();
>   	trace_suspend_resume(TPS("freeze_processes"), 0, false);
> -	if (!error)
> -		return 0;
> +	if (error)
> +		goto Restore;
> +	error = pm_notifier_call_chain_robust(PM_SUSPEND_POST_FREEZE, PM_POST_SUSPEND);
> +	if (error)
> +		goto Thaw;
>   
> -	dpm_save_failed_step(SUSPEND_FREEZE);
> -	pm_notifier_call_chain(PM_POST_SUSPEND);
> +	return 0;
> + Thaw:
> +	suspend_thaw_processes();
>    Restore:
>   	pm_restore_console();
> +	dpm_save_failed_step(SUSPEND_FREEZE);
>   	return error;
>   }
>