linux-kernel - Re: [PATCH v2 0/4] thermal: core/ACPI: Fix processor cooling device regression

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Message-ID: <043b2c3e3024ffaeca69046ae546303ff65694ed.camel@intel.com>
Date:   Mon, 13 Mar 2023 16:47:12 +0000
From:   "Zhang, Rui" <rui.zhang@...el.com>
To:     "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>
CC:     "srinivas.pandruvada@...ux.intel.com" 
        <srinivas.pandruvada@...ux.intel.com>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "Wang, Quanxian" <quanxian.wang@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2 0/4] thermal: core/ACPI: Fix processor cooling device
 regression

Hi, Rafael,

The only concern to me is that, in thermal_cooling_device_update(), we
should handle the cases that the cooling device is current used by
one/more thermal zone. say, something like

list_for_each_entry(pos, &cdev->thermal_instances, cdev_node) {
	/* e.g. what to do if tz1 set it to state 1 previously */
}
I have not got a clear idea what we should do here.

But given that I have confirmed that this patch series fixes the
original problem, and the ACPI passive cooling is unlikely to be
triggered before CPUFREQ_CREATE_POLICY notification, probably we can
address that problem later.

Tested-by: Zhang Rui <rui.zhang@...el.com>
Reviewed-by: Zhang Rui <rui.zhang@...el.com>

thanks,
rui

On Mon, 2023-03-13 at 15:24 +0100, Rafael J. Wysocki wrote:
> Hi All,
> 
> The first revision of this patch series was posted as
> 
> https://lore.kernel.org/linux-pm/2148907.irdbgypaU6@kreacher/
> 
> As reported by Rui in this thread:
> 
> Link: 
> https://lore.kernel.org/linux-pm/53ec1f06f61c984100868926f282647e57ecfb2d.camel@intel.com/
> 
> some recent changes in the thermal core cause the CPU cooling devices
> registered by the ACPI processor driver to become unusable in some
> cases
> and somewhat crippled in general.
> 
> The problem is that the ACPI processor driver changes its
> ->get_max_state()
> callback return value depending on whether or not cpufreq is
> available and
> there is a cpufreq policy for a given CPU.  However, the thermal core
> has
> always assumed that the return value of that callback will not
> change, which
> in fact is relied on by the cooling device statistics code.  In
> particular,
> when the ->get_max_state() grows, the memory buffer allocated for
> storing the
> statistics will be too small and corruption may ensue as a result.
> 
> For this reason, the issue needs to be addressed in the ACPI
> processor driver
> and not in the thermal core, but the core needs to help somewhat
> too.  Namely,
> it needs to provide a helper allowing an interested driver to update
> the
> max_state value for an already registered cooling device in certain
> situations
> which will also cause the statistics to be rebuilt.
> 
> This series implements the above and for details please refer to the
> individual
> patch chagelogs.
> 
> Thanks!
> 
> 
>