linux-kernel - Re: [PATCH] clockevents/drivers/cs5535: improve resilience to spurious interrupts

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Date:   Fri, 20 Oct 2017 08:46:15 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     David Kozub <zub@...ux.fjfi.cvut.cz>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clockevents/drivers/cs5535: improve resilience to
 spurious interrupts

On 20/10/2017 00:25, Thomas Gleixner wrote:
> On Fri, 20 Oct 2017, Daniel Lezcano wrote:
> 
>> On 19/10/2017 22:57, David Kozub wrote:
>>> This solves a BUG on ALIX 2c3 where mfgpt_tick is called before
>>> clockevents_config_and_register returns. This caused mfgpt_tick to call a
>>> null function pointer.
>>>
>>> Thanks to Daniel Lezcano and Thomas Gleixner for helping me analyze this
>>> and suggesting a solution.
>>>
>>> Suggested-by: Thomas Gleixner <tglx@...utronix.de>
>>> Signed-off-by: David Kozub <zub@...ux.fjfi.cvut.cz>
>>> ---
>>
>> Thank for sending this fix.
>>
>> Can you check if the commit 8f9327cbb is the one introducing the
>> regression ? So we can add the proper tags and propagate the fix to stable.
> 
> No it's not.
> 
> -       if (cs5535_tick_mode == CLOCK_EVT_MODE_SHUTDOWN)
> +       if (clockevent_state_shutdown(&cs5535_clockevent))
> 
> This particular problem of the missing detached state check has been there
> forever and went unnoticed for whatever reason.

The detached condition was artificially caught by the initialized variable:

-static unsigned int cs5535_tick_mode = CLOCK_EVT_MODE_SHUTDOWN;

The patch 8f9327cbb removes the variable, so very likely this is where
the problem appeared.


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