Messages in this thread | | | Date | Fri, 8 Mar 2013 17:47:49 +0100 | From | Borislav Petkov <> | Subject | Re: Uhhuh. NMI received for unknown reason 2c on CPU 0. |
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On Wed, Mar 06, 2013 at 01:19:32AM +0100, Borislav Petkov wrote: > On Wed, Mar 06, 2013 at 01:13:23AM +0100, Rafael J. Wysocki wrote: > > I suspected that during resume from hibernation the boot kernel (the > > one that loaded the image) did something to hardware and the restored > > kernel didn't handle that change properly. It is hard do say what > > piece of hardware that was, however (it might or might not be the NIC, > > it may be pure coincidence that the NMI messages appear in the log at > > this point). > > Agreed with the second part. About the first part, who communicates what > to whom, come to think of it, it might not be related to any devices at > all. > > Here's why I think so: > > So one of the things I did to trigger this is boot the machine, run > powertop and set all the knobs in the "Tunables" tab to "Good". One of > the tunables is turn-off-nmi-watchdog something which turns off the > watchdog which is using the perf infrastructure which generates NMIs > when the counter overflows. > > Now, imagine I do that in the "normal" kernel, then suspend, > ...<something happens or does not happen>, then resume back into the > normal kernel and it somehow "forgets" the fact that we disabled the NMI > watchdog before the suspend cycle. And boom, it gets a single spurious > NMI. > > Does it make sense? I dunno - I'm just connecting the dots here between > the observation points which are most likely. > > Anyway, it's getting late, good night. :)
Exactly as I thought: so I'm running the machine with NMI watchdog enabled, i.e. powertop says:
PowerTOP v2.0 Overview Idle stats Frequency stats Device stats Tunables
>> Bad NMI watchdog should be turned off Good VM writeback timeout ....
and no more spurious NMIs.
I'd say the plot thickens: disabling NMIs and suspending to disk right afterwards doesn't seem to really disable the watchdog. Or the disable gets delayed leading to one last spurious NMI when resuming... I probably need to go stare at the code though...
-- Regards/Gruss, Boris.
Sent from a fat crate under my desk. Formatting is fine. --
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