linux-kernel - Re: [PATCH v2 04/12] thermal: core: Mark thermal zones as initializing to start with

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Message-ID: <3b9688a6-517a-4317-8f59-8476e0462a40@arm.com>
Date: Mon, 21 Oct 2024 23:26:05 +0100
From: Lukasz Luba <lukasz.luba@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux PM <linux-pm@...r.kernel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, Zhang Rui <rui.zhang@...el.com>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v2 04/12] thermal: core: Mark thermal zones as
 initializing to start with



On 10/4/24 20:15, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> After thermal_zone_device_register_with_trips() has called
> device_register() and it has registered the new thermal zone device
> with the driver core, user space may access its sysfs attributes and,
> among other things, it may enable the thermal zone before it is ready.
> 
> To address this, introduce a new thermal zone state flag for
> initialization and set it before calling device_register() in
> thermal_zone_device_register_with_trips().  This causes
> __thermal_zone_device_update() to return early until the new flag
> is cleared.
> 
> To clear it when the thermal zone is ready, introduce a new
> function called thermal_zone_init_complete() that will also invoke
> __thermal_zone_device_update() after clearing that flag (both under the
> thernal zone lock) and make thermal_zone_device_register_with_trips()
> call the new function instead of checking need_update and calling
> thermal_zone_device_update() when it is set.
> 
> After this change, if user space enables the thermal zone prematurely,
> __thermal_zone_device_update() will return early for it until
> thermal_zone_init_complete() is called.  In turn, if the thermal zone
> is not enabled by user space before thermal_zone_init_complete() is
> called, the __thermal_zone_device_update() call in it will return early
> because the thermal zone has not been enabled yet, but that function
> will be invoked again by thermal_zone_device_set_mode() when the thermal
> zone is enabled and it will not return early this time.
> 
> The checking of need_update is not necessary any more because the
> __thermal_zone_device_update() calls potentially triggered by cooling
> device binding take place before calling thermal_zone_init_complete(),
> so they all will return early, which means that
> thermal_zone_init_complete() must call __thermal_zone_device_update()
> in case the thermal zone is enabled prematurely by user space.
> 
> Fixes: 203d3d4aa482 ("the generic thermal sysfs driver")
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> This is a new iteration of
> 
> https://lore.kernel.org/linux-pm/2973309.e9J7NaK4W3@rjwysocki.net/
> 
> v1 -> v2: Rebase and add a Fixes tag.
> 
> ---
>   drivers/thermal/thermal_core.c |   16 +++++++++++++---
>   drivers/thermal/thermal_core.h |    1 +
>   2 files changed, 14 insertions(+), 3 deletions(-)
> 
> Index: linux-pm/drivers/thermal/thermal_core.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_core.c
> +++ linux-pm/drivers/thermal/thermal_core.c
> @@ -1332,6 +1332,16 @@ int thermal_zone_get_crit_temp(struct th
>   }
>   EXPORT_SYMBOL_GPL(thermal_zone_get_crit_temp);
>   
> +static void thermal_zone_init_complete(struct thermal_zone_device *tz)
> +{
> +	mutex_lock(&tz->lock);
> +
> +	tz->state &= ~TZ_STATE_FLAG_INIT;
> +	__thermal_zone_device_update(tz, THERMAL_EVENT_UNSPECIFIED);
> +
> +	mutex_unlock(&tz->lock);
> +}
> +
>   /**
>    * thermal_zone_device_register_with_trips() - register a new thermal zone device
>    * @type:	the thermal zone device type
> @@ -1451,6 +1461,8 @@ thermal_zone_device_register_with_trips(
>   	tz->passive_delay_jiffies = msecs_to_jiffies(passive_delay);
>   	tz->recheck_delay_jiffies = THERMAL_RECHECK_DELAY;
>   
> +	tz->state = TZ_STATE_FLAG_INIT;
> +
>   	/* sys I/F */
>   	/* Add nodes that are always present via .groups */
>   	result = thermal_zone_create_device_groups(tz);
> @@ -1504,9 +1516,7 @@ thermal_zone_device_register_with_trips(
>   
>   	mutex_unlock(&thermal_list_lock);
>   
> -	/* Update the new thermal zone and mark it as already updated. */
> -	if (atomic_cmpxchg(&tz->need_update, 1, 0))
> -		thermal_zone_device_update(tz, THERMAL_EVENT_UNSPECIFIED);
> +	thermal_zone_init_complete(tz);
>   
>   	thermal_notify_tz_create(tz);
>   
> Index: linux-pm/drivers/thermal/thermal_core.h
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_core.h
> +++ linux-pm/drivers/thermal/thermal_core.h
> @@ -63,6 +63,7 @@ struct thermal_governor {
>   
>   #define	TZ_STATE_FLAG_SUSPENDED	BIT(0)
>   #define	TZ_STATE_FLAG_RESUMING	BIT(1)
> +#define	TZ_STATE_FLAG_INIT	BIT(2)
>   
>   #define TZ_STATE_READY		0
>   
> 
> 
> 

Reviewed-by: Lukasz Luba <lukasz.luba@....com>