Re: Is notify_die being overloaded?

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.

[*] It does not help that IA64 break.b <n> does not store the value of
<n> in cr.iim. All break.b values look like break.b 0. There used
to be code in traps.c to detect this and extract the value of
break.b, but a kprobes patch removed that code.

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