cpus_in_xmon questions

Will Schmidt willschm at us.ibm.com
Wed Aug 27 23:56:28 EST 2003

  Kdb tries to drop all processors into the debugger, and keeps track of
the state of each, so only one is the controlling processor, and thus has
not run into the problems with hvc_console pulling characters away.

> Hi,
> > Also, what is cpus_in_xmon used for? In xmon/xmon.c, it looks like it's
> > used to prevent a CPU from recursively entering xmon. What could cause
> > that, and would an oops or some sort of message be better there? What
> > prevents a UP CPU from doing the same thing?
> That area of code should probably be looked over. Entering xmon
> recursively is bad stuff but we should not lock up silently.
> > In hvc_console.c, if any CPU is in xmon, the thread skips polling for
> > any data. Why?
> Because otherwise both hvc_console and xmon poll for characters. The
> result is you get maybe every second character through to xmon and every
> other gets sucked up by hvc_console running on another cpu.
> Its a hack to use cpus_in_xmon, we should have something more generic so
> kdb can do the right thing here too.
> Anton

willschm at us.ibm.com
Linux on PowerPC-64 Development
IBM Rochester

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