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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Mon, 11 Dec 2023 14:44:51 +0100
Message-ID: <CAJZ5v0g3exHkX6FLsmbYUcOJHstWOfVf_QnEnm8KmqoYCYwdjA@mail.gmail.com>
Subject: Re: [PATCH v1 0/3] thermal: core: Remove thermal zones during unregistration
To:     Lukasz Luba <lukasz.luba@arm.com>
Cc:     "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Linux PM <linux-pm@vger.kernel.org>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Zhang Rui <rui.zhang@intel.com>,
        Linux ACPI <linux-acpi@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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Hi Lukasz,

On Mon, Dec 11, 2023 at 2:37 PM Lukasz Luba <lukasz.luba@arm.com> wrote:
>
> 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@arm.com>

Thank you!