linux-kernel - Re: [PATCH v2 4/6] thermal: core: Store zone ops in struct thermal_zone

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Date: Thu, 22 Feb 2024 11:52:44 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>, Linux PM <linux-pm@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, Linux ACPI <linux-acpi@...r.kernel.org>, 
	Lukasz Luba <lukasz.luba@....com>, Zhang Rui <rui.zhang@...el.com>, 
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, 
	Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Shawn Guo <shawnguo@...nel.org>, 
	Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>, 
	Fabio Estevam <festevam@...il.com>, NXP Linux Team <linux-imx@....com>
Subject: Re: [PATCH v2 4/6] thermal: core: Store zone ops in struct thermal_zone_device

On Thu, Feb 22, 2024 at 11:47 AM Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
>
> On 14/02/2024 13:45, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> > The current code requires thermal zone creators to pass pointers to
> > writable ops structures to thermal_zone_device_register_with_trips()
> > which needs to modify the target struct thermal_zone_device_ops object
> > if the "critical" operation in it is NULL.
> >
> > Moreover, the callers of thermal_zone_device_register_with_trips() are
> > required to hold on to the struct thermal_zone_device_ops object passed
> > to it until the given thermal zone is unregistered.
> >
> > Both of these requirements are quite inconvenient, so modify struct
> > thermal_zone_device to contain struct thermal_zone_device_ops as field and
> > make thermal_zone_device_register_with_trips() copy the contents of the
> > struct thermal_zone_device_ops passed to it via a pointer (which can be
> > const now) to that field.
> >
> > Also adjust the code using thermal zone ops accordingly and modify
> > thermal_of_zone_register() to use a local ops variable during
> > thermal zone registration so ops do not need to be freed in
> > thermal_of_zone_unregister() any more.
>
> [ ... ]
>
> >   static void thermal_of_zone_unregister(struct thermal_zone_device *tz)
> >   {
> >       struct thermal_trip *trips = tz->trips;
> > -     struct thermal_zone_device_ops *ops = tz->ops;
> >
> >       thermal_zone_device_disable(tz);
> >       thermal_zone_device_unregister(tz);
> >       kfree(trips);
>
> Not related to the current patch but with patch 1/6. Freeing the trip
> points here will lead to a double free given it is already freed from
> thermal_zone_device_unregister() after the changes introduces in patch
> 1, right ?

No, patch [1/6] doesn't free the caller-supplied ops, just copies them
into the local instance.  Attempting to free a static ops would not be
a good idea, for example.

BTW, thanks for all of the reviews, but this series is not applicable
without the one at

https://lore.kernel.org/linux-pm/6017196.lOV4Wx5bFT@kreacher/