From: Dmitry Osipenko <digetx@gmail.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Viresh Kumar <vireshk@kernel.org>, Nishanth Menon <nm@ti.com>,
Stephen Boyd <sboyd@kernel.org>,
linux-pm@vger.kernel.org,
Vincent Guittot <vincent.guittot@linaro.org>,
Rafael Wysocki <rjw@rjwysocki.net>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] opp: Prepare for ->set_opp() helper to work without regulators
Date: Wed, 20 Jan 2021 17:50:15 +0300 [thread overview]
Message-ID: <94f4ed8d-ab54-4180-87f7-4ddafb52074f@gmail.com> (raw)
In-Reply-To: <20210120073912.yl4rgkthdyyznbfh@vireshk-i7>
20.01.2021 10:39, Viresh Kumar пишет:
> On 19-01-21, 20:16, Dmitry Osipenko wrote:
>> 19.01.2021 09:35, Viresh Kumar пишет:
>>> + mutex_lock(&opp_table->lock);
>>> + opp_table->set_opp_data = data;
>>> + if (opp_table->sod_supplies) {
>>> + data->old_opp.supplies = opp_table->sod_supplies;
>>> + data->new_opp.supplies = opp_table->sod_supplies +
>>> + opp_table->regulator_count;
>>> + }
>>> + mutex_unlock(&opp_table->lock);
>>
>> Why do we need all these locks in this patch?
>
> In case dev_pm_opp_set_regulators() and
> dev_pm_opp_register_set_opp_helper() get called at the same time.
> Which can actually happen, though is a corner case.
>
>> The OPP API isn't thread-safe, these locks won't make the API
>> thread-safe.
>
> I am not sure what you mean by that, can you please explain ?
>
>> At least both sod_supplies and set_opp() pointers should be
>> set and unset under the lock.
>
> The ->set_opp pointer isn't getting used for a comparison and so
> putting that inside a lock won't get us anything. We are only using
> set_opp_data and sod_supplies for comparison at both the places and so
> they need to be updated within the lock.
>
If OPP API was meant to be thread-safe, then the
dev_pm_opp_unregister_set_opp_helper() should unset the
opp_table->set_opp_data under the lock since it races with
dev_pm_opp_set_regulators().
Secondly, functions like dev_pm_opp_set_rate() don't have any locks at all.
It should be better not to add "random" locks into the code because it
only creates an illusion for an oblivious API user that OPP API cares
about thread safety, IMO.
Making OPP API thread-safe will take some effort and a careful review of
every lock will be needed.
next prev parent reply other threads:[~2021-01-20 15:37 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-18 0:55 [PATCH v3 00/12] OPP API fixes and improvements Dmitry Osipenko
2021-01-18 0:55 ` [PATCH v3 01/12] opp: Fix adding OPP entries in a wrong order if rate is unavailable Dmitry Osipenko
2021-01-18 7:44 ` Viresh Kumar
2021-01-18 18:46 ` Dmitry Osipenko
2021-01-18 0:55 ` [PATCH v3 02/12] opp: Filter out OPPs based on availability of a required-OPP Dmitry Osipenko
2021-01-18 8:11 ` Viresh Kumar
2021-01-18 0:55 ` [PATCH v3 03/12] opp: Correct debug message in _opp_add_static_v2() Dmitry Osipenko
2021-01-18 8:14 ` Viresh Kumar
2021-01-18 0:55 ` [PATCH v3 04/12] opp: Add dev_pm_opp_sync_regulators() Dmitry Osipenko
2021-01-18 8:20 ` Viresh Kumar
2021-01-18 18:35 ` Dmitry Osipenko
2021-01-19 4:58 ` Viresh Kumar
2021-01-19 22:42 ` Dmitry Osipenko
2021-01-18 11:00 ` Viresh Kumar
2021-01-18 11:06 ` Viresh Kumar
2021-01-18 0:55 ` [PATCH v3 05/12] opp: Add dev_pm_opp_set_voltage() Dmitry Osipenko
2021-01-18 9:52 ` Viresh Kumar
2021-01-18 19:14 ` Dmitry Osipenko
2021-01-20 21:57 ` Dmitry Osipenko
2021-01-21 11:20 ` Viresh Kumar
2021-01-18 0:55 ` [PATCH v3 06/12] opp: Add dev_pm_opp_find_level_ceil() Dmitry Osipenko
2021-01-18 9:58 ` Viresh Kumar
2021-01-18 0:55 ` [PATCH v3 07/12] opp: Add dev_pm_opp_get_required_pstate() Dmitry Osipenko
2021-01-18 10:50 ` Viresh Kumar
2021-01-18 0:55 ` [PATCH v3 08/12] opp: Add devm_pm_opp_register_set_opp_helper Dmitry Osipenko
2021-01-18 11:07 ` Viresh Kumar
2021-01-18 0:55 ` [PATCH v3 09/12] opp: Add devm_pm_opp_attach_genpd Dmitry Osipenko
2021-01-18 11:14 ` Viresh Kumar
2021-01-18 0:55 ` [PATCH v3 10/12] opp: Support set_opp() customization without requiring to use regulators Dmitry Osipenko
2021-01-18 11:44 ` Viresh Kumar
2021-01-18 18:48 ` Dmitry Osipenko
2021-01-19 6:35 ` [PATCH] opp: Prepare for ->set_opp() helper to work without regulators Viresh Kumar
2021-01-19 17:16 ` Dmitry Osipenko
2021-01-20 7:39 ` Viresh Kumar
2021-01-20 14:50 ` Dmitry Osipenko [this message]
2021-01-21 11:25 ` Viresh Kumar
2021-01-19 17:18 ` Dmitry Osipenko
2021-01-20 8:08 ` Viresh Kumar
2021-01-21 11:28 ` Viresh Kumar
2021-01-19 6:36 ` [PATCH v3 10/12] opp: Support set_opp() customization without requiring to use regulators Viresh Kumar
2021-01-21 11:30 ` [PATCH V2] opp: Prepare for ->set_opp() helper to work without regulators Viresh Kumar
2021-01-21 21:02 ` Dmitry Osipenko
2021-01-22 3:05 ` Viresh Kumar
2021-01-18 0:55 ` [PATCH v3 11/12] opp: Handle missing OPP table in dev_pm_opp_xlate_performance_state() Dmitry Osipenko
2021-01-18 11:18 ` Viresh Kumar
2021-01-18 0:55 ` [PATCH v3 12/12] opp: Print OPP level in debug message of _opp_add_static_v2() Dmitry Osipenko
2021-01-18 11:18 ` Viresh Kumar
2021-01-18 11:46 ` [PATCH v3 00/12] OPP API fixes and improvements Viresh Kumar
2021-01-19 17:35 ` Dmitry Osipenko
2021-01-20 15:41 ` Dmitry Osipenko
2021-01-21 7:51 ` Viresh Kumar
2021-01-21 20:30 ` Dmitry Osipenko
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