linux-kernel - Re: [PATCH v5 05/11] ACPI: thermal: Carry out trip point updates under zone lock

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Date:   Wed, 16 Aug 2023 18:25:30 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux ACPI <linux-acpi@...r.kernel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Michal Wilczynski <michal.wilczynski@...el.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v5 05/11] ACPI: thermal: Carry out trip point updates
 under zone lock

On 07/08/2023 20:08, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> There is a race condition between acpi_thermal_trips_update() and
> acpi_thermal_check_fn(), because the trip points may get updated while
> the latter is running which in theory may lead to inconsistent results.
> For example, if two trips are updated together, using the temperature
> value of one of them from before the update and the temperature value
> of the other one from after the update may not lead to the expected
> outcome.
> 
> Moreover, if thermal_get_trend() runs when a trip points update is in
> progress, it may end up using stale trip point temperatures.
> 
> To address this, make acpi_thermal_trips_update() call
> thermal_zone_device_adjust() to carry out the trip points update and
> provide a new  acpi_thermal_adjust_thermal_zone() wrapper around
> __acpi_thermal_trips_update() as the callback function for the latter.
> 
> While at it, change the acpi_thermal_trips_update() return data type
> to void as that function always returns 0 anyway.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---

[ ... ]

>   {
> -	int i, ret = acpi_thermal_trips_update(tz, ACPI_TRIPS_INIT);
>   	bool valid;
> +	int i;
>   
> -	if (ret)
> -		return ret;
> +	__acpi_thermal_trips_update(tz, ACPI_TRIPS_INIT);
>   
>   	valid = tz->trips.critical.valid |
>   		tz->trips.hot.valid |
> @@ -710,6 +732,7 @@ static struct thermal_zone_device_ops ac
>   	.get_trend = thermal_get_trend,
>   	.hot = acpi_thermal_zone_device_hot,
>   	.critical = acpi_thermal_zone_device_critical,
> +	.update = acpi_thermal_adjust_thermal_zone,

It is too bad we have to add a callback in the core code just for this 
driver.

I'm wondering if it is not possible to get rid of it ?

Is it possible to use an internal lock for the ACPI driver to solve the 
race issue above ?



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