linux-kernel - Re: [PATCH v1 0/3] thermal: core: Remove thermal zones during unregistration

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Message-ID: <a317fd5b-85df-409f-96e2-8123eea6ca73@arm.com>
Date:   Mon, 11 Dec 2023 13:38:16 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 0/3] thermal: core: Remove thermal zones during
 unregistration

Hi Rafael,

On 12/8/23 19:11, Rafael J. Wysocki wrote:
> Hi All,
> 
> This patch series adds a mechanism to guarantee that
> thermal_zone_device_unregister() will not return until all of the active
> references to the thermal zone device object in question have been dropped
> and it has been deleted (patch [1/3]).
> 
> This supersedes the approach used so far in which all thermal zone sysfs
> attribute callbacks check if the zone device is still registered under the
> zone lock, so as to return early if that is not the case, as it means that
> device_del() has been called for the thermal zone in question (and returned).
> It is not necessary to do that any more after patch [1/3], so patch [2/3]
> removes those checks from the code and drops zone locking that is not
> necessary any more either.
> 
> Patch [3/3] uses the observation that the thermal subsystem does not need to
> check if a thermal zone device is registered at all, because it can use its
> own data to determine whether or not the thermal zone is going away and so
> it may not be worth updating it, for example.
> 
> Please refer to the patch changelogs for details.
> 
> The series depends on new thermal material in linux-next, but it should not
> substantially depend on any changes that have not made it into linux-next yet.
> 
> Thanks!
> 
> 
> 

I like the concept with completion thing for this.
I have tired to stress test these patches with my mock
thermal zone module load/unload and it works good.

The test was doing the these bits:
for i in $(seq 1 1000000) ; do cat 
/sys/class/thermal/thermal_zone2/trip_point_0_temp > /dev/null 2>&1 ; done &
for i in $(seq 1 10000) ; do insmod /data/selftest_ipa.ko ; rmmod 
selftest_ipa ; done &

I couldn't trigger any issues in reading from this
trip temp file in background, which should go now w/o the
locking. I thought it would be nice test, since we have
direct call to trips array 'tz->trips[trip_id].temperature'.
Let me know if you think about other scenario for stress testing it.
(I have also checked the 'temp' sysfs read, where the mutex for
tz is used - also no issues).

Feel free to add to all patches:

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

Regards,
Lukasz