Messages in this thread | | | Date | Sat, 9 Nov 2013 15:20:59 +0100 | From | Frederic Weisbecker <> | Subject | Re: perf/tracepoint: another fuzzer generated lockup |
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On Sat, Nov 09, 2013 at 03:10:39PM +0100, Peter Zijlstra wrote: > On Fri, Nov 08, 2013 at 11:36:58PM +0100, Frederic Weisbecker wrote: > > [ 237.627769] perf samples too long (3397569 > 2500), lowering kernel.perf_event_max_sample_rate to 50000 > > [ 237.637124] INFO: NMI handler (perf_event_nmi_handler) took too long to run: 444.233 msecs > > > > 444 msecs is huge. > > Be glad your system lived to tell about it ;-) Calling printk() from NMI > context is Russian roulette; I'm still waiting for the first report it > actually locked up :-)
Haha, right. I dump with earlyprintk but that doesn't change the fact it passes through printk machinery. Fortunately I haven't yet got burdened with that. Although... maybe printk plays a role in the issue here...
> > That said, I'm not sure what kernel you're running, but there were some > issues with time-keeping hereabouts, but more importantly that second > timing includes the printk() call of the first -- so that's always going > to be fucked.
It's a recent tip:master. So the delta debug printout is certainly buggy, meanwhile these lockup only happen with Vince selftests, and they trigger a lot of these NMI-too-long issues, or may be that's the other way round :)...
I'm trying to narrow down the issue, lets hope the lockup is not actually due to printk itself.
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