When a MetaIRQ preempts a cooperative thread, that thread would be
added back to the generic run queue. When the MetaIRQ is done, the
highest priority thread will be selected to run, which may obviously
be a cooperative thread of a higher priority than the one that was
preempted.
But that's wrong, because the original thread was promised that it
would NOT be preempted until it reached a scheduling point on its own
(that's the whole point of a cooperative thread, of course).
We need to track the thread that got preempted (one per CPU) and
return to it instead of whatever else the scheduler might have found.
Fixes#20255
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
11a050b2c3