linux-kernel - Re: intel_pstate_timer_func divide by zero oops

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Date:	Wed, 27 Mar 2013 23:13:45 -0400
From:	Parag Warudkar <parag.lkml@...il.com>
To:	Dirk Brandewie <dirk.brandewie@...il.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: intel_pstate_timer_func divide by zero oops

On Wed, Mar 27, 2013 at 10:51 PM, Dirk Brandewie
<dirk.brandewie@...il.com> wrote:
>
> Is there any way to capture the beginning of this trace?

I tried but since the oops scrolls fast followed by a hard freeze, I
wasn't able to capture it completely.
May be I can try netconsole and see if that helps.

>
> pid_param_set() is on the stack which means that something is changing
> the debugfs parameters or the stack is FUBAR.
>
I somehow doubt the stack is messed up as the call traces are always identical.
(pid_param_set() seems to be in first trace as well.)

>
> I don't see how duration_us can be zero unless somehow I am getting
> back-to-back
> timer callbacks which seems unlikely since the timer is not re-armed until
> the timer function is about to return and the driver has done all its work
> for the sample period

Do the two oops with common call stack suggest back to back callbacks?

I will add some debugging checks tomorrow to see what is going on. But
sounds like a minimal fix would be to guard against callbacks in quick
succession?
i.e. return from sample if ktime_us_delta(now, cpu->prev_sample) is zero?

Thanks,
Parag
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