From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dirk Brandewie Subject: Re: intel_pstate_timer_func divide by zero oops Date: Thu, 28 Mar 2013 08:35:53 -0700 Message-ID: <51546359.8000002@gmail.com> References: <5153B03E.2050201@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: cpufreq-owner@vger.kernel.org To: Parag Warudkar Cc: Dirk Brandewie , "Rafael J. Wysocki" , cpufreq@vger.kernel.org, linux-pm@vger.kernel.org, LKML , Linus Torvalds List-Id: linux-pm@vger.kernel.org On 03/27/2013 08:13 PM, Parag Warudkar wrote: > On Wed, Mar 27, 2013 at 10:51 PM, Dirk Brandewie > 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 agree that the two oops are likely the same but unless something is crawling through debugfs writing random values to the files there pid_param_set() should not be on any stack anywhere. There was a similar bug reported by fedora: https://bugzilla.redhat.com/show_bug.cgi?id=920289 This bug has not showed up again since rc3 can you try the current rc to see if you still see the problem? >> >> 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 >