Re: Is notify_die being overloaded?

[Keith Owens <kaos@sgi.com>]

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.