[Xenomai-core] [RFC] Fixes for domain migration races

[Jan Kiszka <jan.kiszka@domain.hid>]

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Hi,

I've just uploaded my upstream queue that mostly deals with the various
races I found in the domain migration code.

One of my concerns raised earlier turned out to be for no reason: We do
not allow Linux to wake up a task that has TASK_ATOMICSWITCH set. So the
deletion race can indeed be fixed by the patch I sent earlier. However,
we do not synchronize setting and testing of TASK_ATOMICSWITCH (because
we cannot hold the rq lock), thus we still face a small race window that
allows premature wakeups, at least in theory. That's now addressed by
patch 3.

Besides another race around set/clear_task_nowakeup, there should have
been a window during early migration to RT where we silently swallowed
Linux signals. Closed by patch 4, hopefully also fixing our spurious gdb
lockups on SMP boxes - time will tell.

Please review carefully.

Jan


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