From: Quentin Perret <qperret@google.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Arnd Bergmann <arnd@arndb.de>,
Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux PM <linux-pm@vger.kernel.org>,
"Cc: Android Kernel" <kernel-team@android.com>,
Todd Kjos <tkjos@google.com>,
adharmap@codeaurora.org
Subject: Re: [PATCH v2 2/2] cpufreq: Specify default governor on command line
Date: Wed, 24 Jun 2020 16:32:59 +0100 [thread overview]
Message-ID: <20200624153259.GA2844@google.com> (raw)
In-Reply-To: <CAJZ5v0ja_rM7i=psW1HRyzEpW=8QwP2u9p+ihN3FS8_53bbxTQ@mail.gmail.com>
On Wednesday 24 Jun 2020 at 14:51:04 (+0200), Rafael J. Wysocki wrote:
> On Wed, Jun 24, 2020 at 7:50 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
> > > @@ -2789,7 +2796,13 @@ static int __init cpufreq_core_init(void)
> > > cpufreq_global_kobject = kobject_create_and_add("cpufreq", &cpu_subsys.dev_root->kobj);
> > > BUG_ON(!cpufreq_global_kobject);
> > >
> > > + mutex_lock(&cpufreq_governor_mutex);
> > > + if (!default_governor)
> > > + default_governor = cpufreq_default_governor();
> > > + mutex_unlock(&cpufreq_governor_mutex);
> >
> > I don't think locking is required here at core-initcall level.
>
> It isn't necessary AFAICS, but it may as well be regarded as
> annotation (kind of instead of having a comment explaining why it need
> not be used).
Right, but I must admit that, looking at this more, I'm getting a bit
confused with the overall locking for governors :/
When in cpufreq_init_policy() we find a governor using
find_governor(policy->last_governor), what guarantees this governor is
not concurrently unregistered? That is, what guarantees this governor
doesn't go away between that find_governor() call, and the subsequent
call to try_module_get() in cpufreq_set_policy() down the line?
Can we somewhat assume that whatever governor is referred to by
policy->last_governor will have a non-null refcount? Or are the
cpufreq_online() and cpufreq_unregister_governor() path mutually
exclusive? Or is there something else?
Thanks,
Quentin
next prev parent reply other threads:[~2020-06-24 15:33 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-23 14:21 [PATCH v2 0/2] cpufreq: Specify the default governor on command line Quentin Perret
2020-06-23 14:21 ` [PATCH v2 1/2] cpufreq: Register governors at core_initcall Quentin Perret
2020-06-23 14:21 ` [PATCH v2 2/2] cpufreq: Specify default governor on command line Quentin Perret
2020-06-24 5:50 ` Viresh Kumar
2020-06-24 12:51 ` Rafael J. Wysocki
2020-06-24 15:32 ` Quentin Perret [this message]
2020-06-25 8:50 ` Viresh Kumar
2020-06-25 10:52 ` Rafael J. Wysocki
2020-06-25 11:36 ` Viresh Kumar
2020-06-25 11:44 ` Rafael J. Wysocki
2020-06-25 11:53 ` Quentin Perret
2020-06-25 13:28 ` Rafael J. Wysocki
2020-06-25 13:49 ` Quentin Perret
2020-06-25 14:08 ` Rafael J. Wysocki
2020-06-26 2:53 ` Viresh Kumar
2020-06-26 8:09 ` Quentin Perret
2020-06-23 17:54 ` [PATCH v2 0/2] cpufreq: Specify the " Doug Smythies
2020-06-23 18:04 ` Quentin Perret
2020-06-24 0:07 ` Doug Smythies
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