Date:   Sat, 24 Sep 2022 19:46:33 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>, rafael@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        rui.zhang@...el.com, Amit Kucheria <amitk@...nel.org>
Subject: Re: [PATCH v4 01/30] thermal/core: Add a generic
 thermal_zone_get_trip() function

On 24/09/2022 00:19, Marek Szyprowski wrote:
> Hi Daniel,
> 
> On 21.09.2022 11:42, Daniel Lezcano wrote:
>> The thermal_zone_device_ops structure defines a set of ops family,
>> get_trip_temp(), get_trip_hyst(), get_trip_type(). Each of them is
>> returning a property of a trip point.
>>
>> The result is the code is calling the ops everywhere to get a trip
>> point which is supposed to be defined in the backend driver. It is a
>> non-sense as a thermal trip can be generic and used by the backend
>> driver to declare its trip points.
>>
>> Part of the thermal framework has been changed and all the OF thermal
>> drivers are using the same definition for the trip point and use a
>> thermal zone registration variant to pass those trip points which are
>> part of the thermal zone device structure.
>>
>> Consequently, we can use a generic function to get the trip points
>> when they are stored in the thermal zone device structure.
>>
>> This approach can be generalized to all the drivers and we can get rid
>> of the ops->get_trip_*. That will result to a much more simpler code
>> and make possible to rework how the thermal trip are handled in the
>> thermal core framework as discussed previously.
>>
>> This change adds a function thermal_zone_get_trip() where we get the
>> thermal trip point structure which contains all the properties (type,
>> temp, hyst) instead of doing multiple calls to ops->get_trip_*.
>>
>> That opens the door for trip point extension with more attributes. For
>> instance, replacing the trip points disabled bitmask with a 'disabled'
>> field in the structure.
>>
>> Here we replace all the calls to ops->get_trip_* in the thermal core
>> code with a call to the thermal_zone_get_trip() function.
>>
>> While at it, add the thermal_zone_get_num_trips() to encapsulate the
>> code more and reduce the grip with the thermal framework internals.
>>
>> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> 
> This patch landed in linux next-20220923 as commit 78ffa3e58d93
> ("thermal/core: Add a generic thermal_zone_get_trip() function").
> Unfortunately it introduces a deadlock:
> 
> thermal_zone_device_update() calls handle_thermal_trip() under the
> tz->lock, which in turn calls thermal_zone_get_trip(), which gathers
> again tz->lock. I've tried to fix this by switching
> handle_thermal_trip() to call __thermal_zone_get_trip().
> 
> This helps for fixing the issue in this change, but then I've tried to
> apply it on top of linux next-20220923. Unfortunately it fails again. It
> looks that the other changes also assumes that calling
> thermal_zone_get_trip() is possible under the tz->lock, because in my
> case it turned out that handle_non_critical_trips() called
> step_wise_throttle(), which in turn called thermal_zone_get_trip(). I
> gave up fixing this. Please re-check possible call paths and adjust
> locking to them.

Yes, you are correct. Those paths have the lock held. I'm fixing this


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