Messages in this thread | | | Date | Tue, 23 Apr 2024 10:21:39 -0700 | From | Kees Cook <> | Subject | Re: [PATCH] lkdtm/bugs: add test for hung smp_call_function_single() |
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On Tue, Apr 23, 2024 at 10:47:29AM +0100, Mark Rutland wrote: > On Fri, Apr 19, 2024 at 02:53:59PM -0700, Kees Cook wrote: > > On Fri, Apr 19, 2024 at 11:34:52AM +0100, Mark Rutland wrote: > > > The CONFIG_CSD_LOCK_WAIT_DEBUG option enables debugging of hung > > > smp_call_function*() calls (e.g. when the target CPU gets stuck within > > > the callback function). Testing this option requires triggering such > > > hangs. > > > > > > This patch adds an lkdtm test with a hung smp_call_function_single() > > > callbac, which can be used to test CONFIG_CSD_LOCK_WAIT_DEBUG and NMI > > > backtraces (as CONFIG_CSD_LOCK_WAIT_DEBUG will attempt an NMI backtrace > > > of the hung target CPU). > > [...] > > > > I wrote this because I needed to guide someone through debugging a hung > > > smp_call_function() call, and I needed examples with/without an NMI > > > backtrace. It seems like it'd be useful for testing the CSD lockup > > > detector and NMI backtrace code in future. > > > > Like the other lockup detector, I suspect we should skip it by default > > in the selftests? Something like this: > > > > diff --git a/tools/testing/selftests/lkdtm/tests.txt b/tools/testing/selftests/lkdtm/tests.txt > > index 368973f05250..32baddc2c85d 100644 > > --- a/tools/testing/selftests/lkdtm/tests.txt > > +++ b/tools/testing/selftests/lkdtm/tests.txt > > @@ -31,6 +31,7 @@ SLAB_FREE_CROSS > > SLAB_FREE_PAGE > > #SOFTLOCKUP Hangs the system > > #HARDLOCKUP Hangs the system > > +#CSDLOCKUP Hangs the system > > #SPINLOCKUP Hangs the system > > #HUNG_TASK Hangs the system > > EXEC_DATA > > Ah, I wasn't ware of that file, yes. > > > > I'm not sure about the CSDLOCKUP name, but everything else I tried > > > didn't seem great either: > > > > > > * IPILOCKUP sounds like it's testing IPIs generally > > > * SMPCALLLOCKUP and similar look weirdly long > > > * SMP_CALL_LOCKUP and similar look different to {HARD,SOFT,SPIN}LOCKUP > > > > > > ... and I'm happy to defer to Kees for the naming. ;) > > > > It looks like it's only useful with CSD lockup detector? If that's true, > > sure, this name is fine. > > I think it's also useful for testing other things (e.g. RCU stall detection), > so how about we go with SMP_CALL_LOCKUP, as that says what the test does rather > than what specifically it can be used to test?
Yeah, that works for me. Thanks!
-Kees
-- Kees Cook
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