[PATCH] [POWERPC] Rework EXC_LEVEL_EXCEPTION_PROLOG code
benh at kernel.crashing.org
Thu May 1 08:22:10 EST 2008
On Wed, 2008-04-30 at 17:13 -0500, Kumar Gala wrote:
> If we don't handle reschedule or signal will we actually not
> properly? I assume reschedule isn't an issue, but could we lose a
Well, you can be in trouble if you lose TIF_SIGPENDING. You don't -have-
to actually take the signal, it will then be done on the next return to
userspace (next timer interrupt, next syscall, ...), but TIF_SIGPENDING
must not be lost.
> > Nothing specific to your patch, but those level##_STACK_TOP seem to
> > be pretty badly named if you end up -adding- THREAD_SIZE to actually
> > get to the stack's top. Do they really contain the stack top or do
> > they in fact contain the stack base/bottom ?
> That might be stale from how the old code worked. I can never
> remember what we consider the top and bottom of the stack. (please
> remind me and I'll fixup the comments and variables).
Well, top is the high address and bottom is the low address in my view
of things :-)
> I thought about that. The only case its a bit of an issue is for
> CriticalInput. I don't see Watchdog, Debug, or MachineCheck as
> performance critical. I can use r10 if I save and restored the CR
> some other register.
You can save CR first yeah and then interleave a bit using 2 registers
(ie. 2 loads, 2 stores, or something like load 1, load 2, store 1, load
3, store 2, etc...)
> just leaving it to C code. I assume that preempt_count should be
> same value on entry and exit. Do think we should set HARDIRQ_OFFSET
> for debug level exceptions?
Well... I think all those things should run with EE disabled, and thus
be considered as far as linux is concerned, as interrupts. So the C code
should do irq_enter/exit.
> Where should I look for an example of how to convey that information
> to lockdep?
The irqtrace stuff in the asm would do maybe unless transfer_to_handler
does it already, I have to look at the code with all your patches
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