Re: Bug in decr_intr()

[Michael <macallan%netbsd.org@localhost>]

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Hello,

On Sep 8, 2009, at 5:50 PM, Michael wrote:

> I think I just found out why we see occasional, weird panics on SMP  
> PowerPC machines with heavy IO and CPU load - have a look at  
> trap_subr.S - normal external interrupts save a bunch of registers,  
> increment cpuinfo->ci_intr_depth, INTRENTER, call ext_intr(),  
> continue at intr_exit: which restores registers, decrements  
> ci_intr_depth, returns.
> Now the decrementer interrupt does almost the same except that it / 
> doesn't/ increment ci_intr_depth but /does/ branch to intr_exit:, so  
> whenever we take a clock interrupt while working on a hardware  
> interrupt we get ci_intr_depth screwed up which may lead to all  
> kinds of weirdness like soft interrupts running when they shouldn't,  
> hop to the other CPU and whatnot.

> Am I missing something here?

Yup, I am - why on earth do the interrupt handlers jump around like  
that? I didn't see the part that increments ci_intr_depth and then  
branches to decrintr:

> Also, the pri field in clockframe / intrframe is apparently unused,  
> decr_intr() scribbles into it but the value is never used anywhere.

... and this can't cause the problems I'm getting - usually some  
KASSERT that checks if a soft interrupt handler is still on the same  
CPU it started out on.

sorry for the noise :/
Michael

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