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

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Message-ID: <52B367AE.1020500@linaro.org>
Date:	Thu, 19 Dec 2013 22:39:58 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Sören Brinkmann <soren.brinkmann@...inx.com>
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

On 12/19/2013 10:23 PM, Sören Brinkmann wrote:
> 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.

Applied to my tree as a 3.13 fix.

Thanks !
   -- Daniel



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