linux-kernel - Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace timers with utilization ...'

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Message-ID: <6826860.yxabWEoz5T@vostro.rjw.lan>
Date:	Tue, 16 Feb 2016 02:27:15 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Guenter Roeck <linux@...ck-us.net>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	linux-next@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace timers with utilization ...'

On Tuesday, February 16, 2016 06:43:35 AM Viresh Kumar wrote:
> On 15-02-16, 19:41, Rafael J. Wysocki wrote:
> > On Mon, Feb 15, 2016 at 6:05 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> > > [    1.340000] [<c0958e78>] (__cpufreq_driver_target) from [<c095ca58>] (dbs_check_cpu+0x1ac/0x1e8)
> > > [    1.340000] [<c095ca58>] (dbs_check_cpu) from [<c095cd04>] (cpufreq_governor_dbs+0x1fc/0x608)
> > > [    1.340000] [<c095cd04>] (cpufreq_governor_dbs) from [<c0959c5c>] (__cpufreq_governor+0x1a8/0x204)
> > > [    1.340000] [<c0959c5c>] (__cpufreq_governor) from [<c095a2dc>] (cpufreq_init_policy+0x60/0x8c)
> > > [    1.340000] [<c095a2dc>] (cpufreq_init_policy) from [<c095a5f0>] (cpufreq_online+0x2e8/0x708)
> > > [    1.340000] [<c095a5f0>] (cpufreq_online) from [<c075674c>] (subsys_interface_register+0x80/0xc4)
> > > [    1.340000] [<c075674c>] (subsys_interface_register) from [<c0959764>] (cpufreq_register_driver+0x144/0x1a0)
> > 
> > This is the registration of the cpufreq driver (cpufreq-dt in this case).
> > 
> > It does cpufreq_online()->cpufreq_init_policy()->__cpufreq_governor()->cpufreq_governor_dbs()->dbs_check_cpu().
> > 
> > The only way that can happen is when cpufreq_set_policy() finds that
> > the "old" and the "new" policies use the same governor, so it goes and
> > calls __cpufreq_governor(policy, CPUFREQ_GOV_LIMITS), but I'm not sure
> > how this is possible during the initialization ATM.
> > 
> > Viresh, any ideas?
> 
> You misread probably.
> 
> During init, policy->gov is NULL and new_policy->gov is set to the
> default one, probably ondemand/conservative. And in that case, we do:
> - INIT
> - START
> - LIMITS

Yes, that's what we should be doing, but it seemed to me that we didn't.

Or maybe the trace just contained the last one, because that's when the
crash happened.

Thanks,
Rafael