Messages in this thread | | | Date | Sat, 9 Nov 2013 15:52:59 +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 :-) > > 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.
So, an idea of what may be happening: an event overflows while FASYNC flag is set so it triggers an irq work to send the signal (kill_fasync). After the irq work triggers, it generates an irq_work_exit event, which in turn overflows and, if it has FASYNC, triggers a new irq work. The irq work triggers and generates an irq work exit event which has FASYNC flag, etc...
Looks like a nice way to deadlock with an infinite loop of irq work.
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