svn commit: r334827 - in head/sys: amd64/amd64 arm/arm dev/hwpmc i386/i386 kern mips/atheros mips/cavium powerpc/powerpc sys

[John Baldwin]

On 6/8/18 12:34 PM, Matthew Macy wrote:
>> The fact that our NMI handler isn't re-entrant can lead to subtle
>> problems. If while executing the NMI handler we hit a dtrace
>> probe or DDB breakpoint, the iret executed upon return to the handler
>> will re-enable NMIs. Then, if a second NMI arrives before the handler
>> for the first has returned, the trapframe will be clobbered. Did you
>> rule out an issue like this?
> 
> No, but it happened instantly on all CPUs an a non-debug kernel 100%
> of the time after I changed pmc_process_interrupt earlier this week.
> My voodoo fix now avoids it. What you're describing sounds episodic
> and doesn't sound like it would be fixed / worked around by my change.

OTOH, a compiler bug will crop up in other places.  It is best to run
it to ground.  Can you describe what the bug was in more detail?
It would probably not be hard to come up with something you can run
creduce against to get down to a test case.  If you do that, the
LLVM folks are quite helpful and able at fixing the issue which fixes
it in more places than just here.

-- 
John Baldwin