This is not a technical argument, but I am not a big fan of hard hanging
the system if you cannot sync all the CPUs. The original intent was to
at least provide a sync error message to the end user after some
reasonable time. Then allow someone to collect any data you can get and
you basically have to reboot. The reboot was never forced, but assumed
the end users of this knew what they were doing in the first place.
Certainly in a completely working system where you use kgdb only for
inspection this is not an issue, unless you use a breakpoint or single
step one of the smp_call functions. As we all know there are lots of
ways to crash a perfectly working system.
We might be best served to add a comment to explain the purpose of
kgdb_arch_pc() and put it in the optional implementation function
headers in include/linux/kgdb.h
On some archs certain exceptions do not report the address that the
exception occurred at when you call instruction_pointer(). This optional
function allows for an arch to perform a "fixup" to get the address the
exception actually occurred at.
Kgdb requires the actual exception address so a sanity check can be
performed to make sure kgdb did not hit an exception while in a chunk of
code kgdb requires for its functionality. If you hit one of these
conditions kgdb makes its best attempt to try to "patch the wound"
inflicted by shooting yourself but at least you get notified vs a silent