From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Linux PM list <linux-pm@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/12] cpufreq: governor: Close dbs_data update race condition
Date: Fri, 19 Feb 2016 03:34:09 +0100 [thread overview]
Message-ID: <CAJZ5v0gbraK-dwsxeAmE-GUxWnoS=5EdOOCKecptDpFPFpKBfA@mail.gmail.com> (raw)
In-Reply-To: <20160219022721.GA16983@vireshk-i7>
On Fri, Feb 19, 2016 at 3:27 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> On 18-02-16, 17:20, Rafael J. Wysocki wrote:
>> On Thu, Feb 18, 2016 at 6:24 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote:
>> > On 18-02-16, 02:19, Rafael J. Wysocki wrote:
>
>> >> @@ -112,7 +112,7 @@ static ssize_t governor_store(struct kob
>> >>
>> >> mutex_lock(&dbs_data->mutex);
>> >>
>> >> - if (gattr->store)
>> >> + if (dbs_data->usage_count && gattr->store)
>> >
>> > That's not gonna be enough. The above lock doesn't guarantee
>> > protection with any such races.
>
> Oops, I completely misread it. Really sorry about that.
>
> But now that I have read the code again, I wonder why we need this protection at
> all. The first thing we do after decrementing the usage_count counter, is we put
> the kobject. Which will ensure that the sysfs files are all gone. So, what is
> the race we are trying to fix then?
The ->store() callbacks for different attributes may do silly stuff
like walking all CPUs in the system and updating per-CPU data for
them. If the dbs_data the callback has been called for is going away,
this is pointless at best and may be actually harmful depending on
what the callback is really doing.
Thanks,
Rafael
next prev parent reply other threads:[~2016-02-19 2:34 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-18 1:17 [PATCH 0/12] cpufreq: More governor code reorganization Rafael J. Wysocki
2016-02-18 1:19 ` [PATCH 1/12] cpufreq: governor: Close dbs_data update race condition Rafael J. Wysocki
2016-02-18 5:24 ` Viresh Kumar
2016-02-18 16:20 ` Rafael J. Wysocki
2016-02-19 2:27 ` Viresh Kumar
2016-02-19 2:34 ` Rafael J. Wysocki [this message]
2016-02-19 3:09 ` Viresh Kumar
2016-02-18 1:20 ` [PATCH 2/12] cpufreq: governor: Move io_is_busy to struct dbs_data Rafael J. Wysocki
2016-02-18 5:28 ` Viresh Kumar
2016-02-18 1:21 ` [PATCH 3/12] cpufreq: governor: Add a ->start callback for governors Rafael J. Wysocki
2016-02-18 5:36 ` Viresh Kumar
2016-02-18 1:22 ` [PATCH 4/12] cpufreq: governor: Drop unused governor callback and data fields Rafael J. Wysocki
2016-02-18 5:37 ` Viresh Kumar
2016-02-18 1:24 ` [PATCH 5/12] cpufreq: ondemand: Drop one more callback from struct od_ops Rafael J. Wysocki
2016-02-18 5:38 ` Viresh Kumar
2016-02-18 1:26 ` [PATCH 6/12] cpufreq: governor: Fix CPU load information updates via ->store Rafael J. Wysocki
2016-02-18 5:44 ` Viresh Kumar
2016-02-18 17:37 ` Rafael J. Wysocki
2016-02-18 1:28 ` [PATCH 7/12] cpufreq: ondemand: Rework the handling of powersave bias updates Rafael J. Wysocki
2016-02-18 5:53 ` Viresh Kumar
2016-02-18 1:30 ` [PATCH 8/12] cpufreq: governor: Make governor private data per-policy Rafael J. Wysocki
2016-02-18 6:03 ` Viresh Kumar
2016-02-18 17:56 ` [PATCH v2 " Rafael J. Wysocki
2016-02-19 2:36 ` Viresh Kumar
2016-02-18 1:31 ` [PATCH 9/12] cpufreq: governor: Move per-CPU data to the common code Rafael J. Wysocki
2016-02-18 6:08 ` Viresh Kumar
2016-02-18 1:32 ` [PATCH 10/12] cpufreq: governor: Relocate definitions of tuners structures Rafael J. Wysocki
2016-02-18 6:09 ` Viresh Kumar
2016-02-18 17:57 ` [PATCH v2 " Rafael J. Wysocki
2016-02-19 2:36 ` Viresh Kumar
2016-02-18 1:33 ` [PATCH 11/12] cpufreq: governor: Make dbs_data_mutex static Rafael J. Wysocki
2016-02-18 6:09 ` Viresh Kumar
2016-02-18 1:38 ` [PATCH 12/12] cpufreq: governor: Narrow down the dbs_data_mutex coverage Rafael J. Wysocki
2016-02-18 6:20 ` Viresh Kumar
2016-02-18 16:32 ` Rafael J. Wysocki
2016-02-18 17:58 ` [PATCH v2 " Rafael J. Wysocki
2016-02-19 2:38 ` Viresh Kumar
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