linux-kernel - Re: [PATCH] clocksource/arm_arch_timer: Don't trace count reader functions

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Message-ID: <a1af63f8-1b3e-a959-d309-7360679739a2@linaro.org>
Date:   Fri, 24 May 2019 12:42:39 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Marc Zyngier <marc.zyngier@....com>,
        Julien Thierry <julien.thierry@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] clocksource/arm_arch_timer: Don't trace count reader
 functions

On 24/05/2019 11:53, Marc Zyngier wrote:
> On 24/05/2019 10:10, Julien Thierry wrote:
>> With v5.2-rc1, The ftrace functions_graph tracer locks up whenever it is
>> enabled on arm64.
>>
>> Since commit 0ea415390cd3 ("clocksource/arm_arch_timer: Use
>> arch_timer_read_counter to access stable counters") a function pointer
>> is consistently used to read the counter instead of potentially
>> referencing an inlinable function.
>>
>> The graph tacers relies on accessing the timer counters to compute the
> 
> nit: tracers
> 
>> time spent in functions which causes the lockup when attempting to trace
>> these code paths.
>>
>> Annontate the arm arch timer counter accessors as notrace.
> 
> nit: Annotate
> 
>>
>> Fixes: 0ea415390cd3 ("clocksource/arm_arch_timer: Use
>>        arch_timer_read_counter to access stable counters")
>> Signed-off-by: Julien Thierry <julien.thierry@....com>
>> Cc: Marc Zyngier <marc.zyngier@....com>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Steven Rostedt <rostedt@...dmis.org>
>> ---

[ ... ]

> Well spotted, thanks Julien.
> 
> Acked-by: Marc Zyngier <marc.zyngier@....com>
> 
> Daniel, can you please pick this up for the next batch of clocksource fixes?

Sure.

I will take care of fixing the comments, no need to resend.

Thanks

  -- Daniel


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