Re: Is notify_die being overloaded?

[Robin Holt <holt@sgi.com>]

On Mon, Apr 17, 2006 at 05:52:10PM +1000, Keith Owens wrote:
> Robin Holt (on Sat, 15 Apr 2006 05:43:56 -0500) wrote:
> >On Sat, Apr 15, 2006 at 04:19:55PM +1000, Keith Owens wrote:
> >> Robin Holt (on Thu, 13 Apr 2006 14:46:44 -0500) wrote:
> >> >notify_die seems to be called to indicate the machine is going down as
> >> >well as there are trapped events for the process.
> >...
> >> The only real problem is the page fault handler event.  All the other
> >...
> >> 
> >> kprobes should be using its own notify chain to trap page faults, and
> >> the handler for that chain should be optimized away when
> >> CONFIG_KPROBES=n or there are no active probes.
> >
> >I realize the page fault handler is the only performance critical event,
> >but don't all the debugging events _REALLY_ deserve a seperate call chain?
> >They are _completely_ seperate and isolated events.  One is a minor event
> >which a small number of other userland processes are concerned with.
> >The other is indicating the machine is about stop running and is only
> >relevant to critical system infrastructure.
> 
> Unfortunately the ebents are ambiguous.  On IA64 BUG() maps to break 0,
> but break 0 is also used for debugging[*].  Which makes it awkward to
> differentiate between a kernel error and a debug event, we have to
> first ask the debuggers if the event if for them then, if the debuggers
> do not want the event, drop into the die_if_kernel event.

I think this still would argue for a notify_debugger() sort of callout
which would read something like:

	if (notify_debugger(...) == NOTIFY_STOP)
		return;
	die_if_kernel(...)

Makes more sense than a notify_die() in there.  Am I missing something?

Thanks,
Robin