linux-kernel - Re: [PATCH v2 3/9] clocksource/cadence_ttc: Store timer frequency in driver data

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Message-ID: <f5bcb974-8645-48d3-b03c-f894c0bb5b7b@DB8EHSMHS014.ehs.local>
Date:	Thu, 19 Dec 2013 13:23:36 -0800
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
CC:	Michal Simek <michal.simek@...inx.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<devicetree@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v2 3/9] clocksource/cadence_ttc: Store timer frequency in
 driver data

Hi Daniel,

On Thu, Dec 19, 2013 at 09:53:14PM +0100, Daniel Lezcano wrote:
> On 12/19/2013 07:32 PM, Sören Brinkmann wrote:
> >Hi Daniel,
> >
> >On Wed, Dec 18, 2013 at 10:58:26PM +0100, Daniel Lezcano wrote:
> >>On 12/18/2013 05:47 PM, Sören Brinkmann wrote:
> >>>Hi Daniel,
> >>>
> >>>On Wed, Dec 18, 2013 at 03:53:51PM +0100, Daniel Lezcano wrote:
> >>>>On 12/17/2013 08:21 PM, Sören Brinkmann wrote:
> >>>>>Hi Daniel,
> >>>>>
> >>>>>On Tue, Nov 26, 2013 at 05:04:50PM -0800, Soren Brinkmann wrote:
> >>>>>>It is not allowed to call clk_get_rate() from interrupt context. To
> >>>>>>avoid such calls the timer input frequency is stored in the driver's
> >>>>>>data struct which makes it accessible to the driver in any context.
> >>>>>>
> >>>>>>Signed-off-by: Soren Brinkmann <soren.brinkmann@...inx.com>
> >>>>>>Acked-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> >>>>>
> >>>>>I doubt that we'll resolve all issues with this series before the
> >>>>>holidays or even the next merge window. Could you take this patch into
> >>>>>your tree for 3.14? It is not directly related to the cpufreq work and
> >>>>>fixes an actual issue that triggers a kernel WARN under some condition
> >>>>>(I missed preserving the details and the trace). That would take the
> >>>>>easy stuff out of the way and we can focus on the more controversial
> >>>>>changes.
> >>>>
> >>>>You are asking to take it for 3.14 but shouldn't it go as a 3.13 fix ?
> >>>
> >>>That's also an option. As I remember, the patch fixes a kernel WARN. The
> >>>system still seemed operational though. Up to you whether this is
> >>>considered severe enough for the 3.13 series. I'm happy either way.
> >>
> >>I was not able to reproduce the WARN with my board.
> >>
> >>Please, could you give the WARN or give the procedure to reproduce it ?
> >
> >I can't either... I thought I saw the WARN on a vanilla kernel during
> >boot (IIRC, when cpuidle started). Is there any chance the timer core
> >calls the timer's set_mode() from interrupt context?
> >Anyway, let's drop it for now. I'll make sure to record more information
> >in case it reappears.
> 
> Finally I was able to reproduce it with the highres timers disabled,
> the periodic tick system and the locks debug.
> 
> Indeed, we are in an interrupt context (IPI) and we are calling
> clk_get_rate in the the set_mode function which in turn ends up by
> getting a mutex... Even if that does not hang, it is a potential
> kernel crash so I will apply the patch with an updated changelog.

Thanks! Kind of comforting to know that the issue I tried to fix actually exists.

	Sören


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