Philippe Gerum authored Oct 01, 2018 and Jan Kiszka committed Oct 17, 2018

Attempting to migrate to the head domain while running on a CPU which
is not in part of the real-time set is a bug, and must be detected by
the core.

Furthermore, for this detection to work, the I-pipe must not BUG()
unconditionally when failing to schedule out such thread in
__ipipe_migrate_head(), but rather let the real-time core handle the
situation (i.e. Xenomai in xnthread_harden()).

Until both changes are in place, running a thread issuing a real-time
call over a non-RT CPU would trigger a BUG() assertion, e.g.:

With kernel parameter "xenomai.supported_cpus=2", running:

$ switchtest --cpu-affinity=0

would lead to:

[   11.681486] kernel BUG at kernel/sched/core.c:5816!
[   11.686343] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM

Signed-off-by: Philippe Gerum <rpm@xenomai.org>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>