From: Nathan Zimmer <nzimmer@sgi.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: <rjw@sisk.pl>, <cpufreq@vger.kernel.org>,
<linux-pm@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 2/2] cpufreq: Convert the cpufreq_driver_lock to use the rcu
Date: Mon, 25 Feb 2013 14:07:31 -0600 [thread overview]
Message-ID: <512BC483.8010101@sgi.com> (raw)
In-Reply-To: <CAKohpom9q93cVD61qeht2WXgA=no64dwXowtMHS0wCy0k6qxXw@mail.gmail.com>
On 02/22/2013 09:39 PM, Viresh Kumar wrote:
> Hi Nathan,
>
> Sorry for pointing out this so late but i still feel we are missing something
> really important.
>
> On 22 February 2013 21:54, Nathan Zimmer <nzimmer@sgi.com> wrote:
>
>> - read_lock_irqsave(&cpufreq_driver_lock, flags);
>> + rcu_read_lock();
>> + freqs->flags = rcu_dereference(cpufreq_driver)->flags;
>> policy = per_cpu(cpufreq_cpu_data, freqs->cpu);
>> - read_unlock_irqrestore(&cpufreq_driver_lock, flags);
>> + rcu_read_unlock();
>> - write_lock_irqsave(&cpufreq_driver_lock, flags);
>> + spin_lock_irqsave(&cpufreq_driver_lock, flags);
>> for_each_cpu(j, policy->cpus) {
>> per_cpu(cpufreq_cpu_data, j) = policy;
>> per_cpu(cpufreq_policy_cpu, j) = policy->cpu;
>> }
>> - write_unlock_irqrestore(&cpufreq_driver_lock, flags);
>> + spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
> Look at how we are protecting cpufreq_cpu_data here. rcu_read_[un]lock()
> only marks the start/end of critical section. How are we sure here that
> cpufreq_cpu_data is not read simultaneously when we are updating it?
>
> rcu lock/unlock only works for cpufreq_driver pointer only and not for
> this data. We still need the same locking for for cpufreq_cpu_data.
>
> What do you say?
That would include putting the lock around the __cpufreq_cpu_get.
But I do think your right.
Perhaps a better way at this point is to have one lock for
cpufreq_cpu_data, and a second with the rcu to protect cpufreq_driver.
next prev parent reply other threads:[~2013-02-25 20:07 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-04 22:45 [PATCH 0/2] cpufreq: cpufreq_driver_lock is hot on large systems Nathan Zimmer
2013-02-04 22:45 ` [PATCH 1/2] cpufreq: Convert the cpufreq_driver_lock to a rwlock Nathan Zimmer
2013-02-05 8:11 ` Viresh Kumar
2013-02-04 22:45 ` [PATCH 2/2] cpufreq: Convert the cpufreq_driver_lock to use the rcu Nathan Zimmer
2013-02-05 1:07 ` [PATCH 0/2] cpufreq: cpufreq_driver_lock is hot on large systems Rafael J. Wysocki
2013-02-05 8:28 ` Viresh Kumar
2013-02-05 10:03 ` Rafael J. Wysocki
2013-02-05 9:58 ` Viresh Kumar
2013-02-05 10:13 ` Rafael J. Wysocki
2013-02-05 14:58 ` Nathan Zimmer
2013-02-05 22:00 ` Rafael J. Wysocki
2013-02-06 2:04 ` [PATCH v2 linux-next " Nathan Zimmer
2013-02-06 2:04 ` [PATCH v2 linux-next 1/2] cpufreq: Convert the cpufreq_driver_lock to a rwlock Nathan Zimmer
2013-02-06 2:47 ` Viresh Kumar
2013-02-06 2:04 ` [PATCH v2 linux-next 2/2] cpufreq: Convert the cpufreq_driver_lock to use the rcu Nathan Zimmer
2013-02-06 2:52 ` Viresh Kumar
2013-02-06 8:51 ` Viresh Kumar
2013-02-06 13:00 ` Rafael J. Wysocki
2013-02-07 23:29 ` Rafael J. Wysocki
2013-02-11 17:13 ` Nathan Zimmer
2013-02-11 19:36 ` Rafael J. Wysocki
2013-02-12 4:03 ` Nathan Zimmer
2013-02-12 15:59 ` Paul E. McKenney
2013-02-13 13:20 ` Rafael J. Wysocki
2013-02-20 23:56 ` [PATCH v3 0/2] cpufreq: cpufreq_driver_lock is hot on large systems Nathan Zimmer
2013-02-20 23:56 ` [PATCH v3 1/2] cpufreq: Convert the cpufreq_driver_lock to a rwlock Nathan Zimmer
2013-02-20 23:56 ` [PATCH v3 2/2] cpufreq: Convert the cpufreq_driver_lock to use the rcu Nathan Zimmer
2013-02-21 5:50 ` Viresh Kumar
2013-02-21 17:49 ` Nathan Zimmer
2013-02-22 16:24 ` [PATCH v4 0/2] cpufreq: cpufreq_driver_lock is hot on large systems Nathan Zimmer
2013-02-22 16:24 ` [PATCH v4 1/2] cpufreq: Convert the cpufreq_driver_lock to a rwlock Nathan Zimmer
2013-02-23 3:57 ` Viresh Kumar
2013-02-22 16:24 ` [PATCH v4 2/2] cpufreq: Convert the cpufreq_driver_lock to use the rcu Nathan Zimmer
2013-02-23 3:39 ` Viresh Kumar
2013-02-25 20:07 ` Nathan Zimmer [this message]
2013-03-11 23:23 ` [PATCH v4 0/2] cpufreq: cpufreq_driver_lock is hot on large systems Rafael J. Wysocki
2013-03-13 20:50 ` Nathan Zimmer
2013-04-01 15:33 ` [PATCH v5] cpufreq: split the cpufreq_driver_lock and use the rcu (was cpufreq: cpufreq_driver_lock is hot on large systems) Nathan Zimmer
2013-04-01 16:28 ` Viresh Kumar
2013-04-01 17:17 ` Nathan Zimmer
2013-04-01 20:11 ` [PATCH v6 0/2] cpufreq: cpufreq_driver_lock is hot on large systems Nathan Zimmer
2013-04-01 20:11 ` [PATCH v6 1/2] cpufreq: split the cpufreq_driver_lock and use the rcu Nathan Zimmer
2013-04-02 5:05 ` Viresh Kumar
2013-04-02 14:55 ` Nathan Zimmer
2013-04-02 14:59 ` Viresh Kumar
2013-04-02 15:40 ` Nathan Zimmer
2013-04-02 15:52 ` Viresh Kumar
2013-04-02 22:57 ` Rafael J. Wysocki
2013-04-03 5:25 ` Viresh Kumar
2013-04-01 20:11 ` [PATCH v6 2/2] cpufreq: covert the cpufreq_data_lock to a spinlock Nathan Zimmer
2013-04-01 20:41 ` Rafael J. Wysocki
2013-04-02 0:56 ` Nathan Zimmer
2013-04-02 5:04 ` Viresh Kumar
2013-04-02 12:48 ` Rafael J. Wysocki
2013-04-02 14:58 ` Nathan Zimmer
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=512BC483.8010101@sgi.com \
--to=nzimmer@sgi.com \
--cc=cpufreq@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pm@vger.kernel.org \
--cc=rjw@sisk.pl \
--cc=viresh.kumar@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).