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From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Sudeep Holla <sudeep.holla@arm.com>,
	Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Linux PM <linux-pm@vger.kernel.org>,
	Linux ACPI <linux-acpi@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Dmitry Osipenko <digetx@gmail.com>
Subject: Re: [RFT][PATCH 0/3] cpufreq / PM: QoS: Introduce frequency QoS and use it in cpufreq
Date: Thu, 17 Oct 2019 18:34:28 +0200	[thread overview]
Message-ID: <CAJZ5v0ixS8ZS93Fgj8XGUMGcLdAy+Fgwp5z3QirccNSiiwLtDA@mail.gmail.com> (raw)
In-Reply-To: <20191017095942.GF8978@bogus>

On Thu, Oct 17, 2019 at 12:00 PM Sudeep Holla <sudeep.holla@arm.com> wrote:
>
> On Thu, Oct 17, 2019 at 03:27:25PM +0530, Viresh Kumar wrote:
> > On 16-10-19, 15:23, Sudeep Holla wrote:
> > > Thanks for the spinning these patches so quickly.
> > >
> > > I did give it a spin, but unfortunately it doesn't fix the bug I reported.
> > > So I looked at my bug report in detail and looks like the cpufreq_driver
> > > variable is set to NULL at that point and it fails to dereference it
> > > while trying to execute:
> > >     ret = cpufreq_driver->verify(new_policy);
> > > (Hint verify is at offset 0x1c/28)
> > >
> > > So I suspect some race as this platform with bL switcher tries to
> > > unregister and re-register the cpufreq driver during the boot.
> > >
> > > I need to spend more time on this as reverting the initial PM QoS patch
> > > to cpufreq.c makes the issue disappear.

I guess you mean commit 67d874c3b2c6 ("cpufreq: Register notifiers
with the PM QoS framework")?

That would make sense, because it added the cpufreq_notifier_min() and
cpufreq_notifier_max() that trigger handle_update() via
schedule_work().

[BTW, Viresh, it looks like cpufreq_set_policy() should still ensure
that the new min is less than the new max, because the QoS doesn't do
that.]

> > Is this easily reproducible ? cpufreq_driver == NULL shouldn't be the case, it
> > get updated only once while registering/unregistering cpufreq drivers. That is
> > the last thing which can go wrong from my point of view :)
> >
>
> Yes, if I boot my TC2 with bL switcher enabled, it always crashes on boot.

It does look like handle_update() races with
cpufreq_unregister_driver() and cpufreq_remove_dev (called from there
indirectly) does look racy.

  reply	other threads:[~2019-10-17 16:34 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-16 10:37 Rafael J. Wysocki
2019-10-16 10:41 ` [RFT][PATCH 1/3] PM: QoS: Introduce frequency QoS Rafael J. Wysocki
2019-10-17  9:41   ` Viresh Kumar
2019-10-17 14:16     ` Rafael J. Wysocki
2019-10-18  5:41       ` Viresh Kumar
2019-10-24 19:01   ` Leonard Crestez
2019-10-24 19:34     ` Leonard Crestez
2019-11-17  7:34   ` Doug Smythies
2019-11-17 16:13   ` Doug Smythies
2019-11-19 14:35     ` Doug Smythies
2019-11-19 19:17       ` Rafael J. Wysocki
2019-11-19 22:13         ` Rafael J. Wysocki
2019-11-20  6:55           ` Doug Smythies
2019-11-20  9:08             ` Rafael J. Wysocki
2019-10-16 10:47 ` [RFT][PATCH 2/3] cpufreq: Use per-policy " Rafael J. Wysocki
2019-10-16 18:01   ` Dmitry Osipenko
2019-10-17 21:29     ` Dmitry Osipenko
2019-10-18  9:29       ` Viresh Kumar
2019-10-18 15:31         ` Dmitry Osipenko
2019-10-16 10:47 ` [RFT][PATCH 3/3] PM: QoS: Drop frequency QoS types from device PM QoS Rafael J. Wysocki
2019-10-16 14:23 ` [RFT][PATCH 0/3] cpufreq / PM: QoS: Introduce frequency QoS and use it in cpufreq Sudeep Holla
2019-10-17  9:57   ` Viresh Kumar
2019-10-17  9:59     ` Sudeep Holla
2019-10-17 16:34       ` Rafael J. Wysocki [this message]
2019-10-17 16:42         ` Sudeep Holla
2019-10-18  5:44         ` Viresh Kumar
2019-10-18  8:24           ` Rafael J. Wysocki
2019-10-18  8:27             ` Viresh Kumar
2019-10-18  8:30               ` Rafael J. Wysocki
2019-10-18  9:24                 ` Viresh Kumar
2019-10-18  9:26                   ` Rafael J. Wysocki
2019-10-18  9:28                     ` Viresh Kumar
2019-10-17 17:14   ` Sudeep Holla
2019-10-17  9:46 ` Viresh Kumar

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