Philippe Gerum authored Jan 14, 2019 and Jan Kiszka committed Mar 18, 2019

The token-based approach for detecting preemption while data is being
moved into or out of the ring only protects from read vs read races,
not from races involving a write side. For instance, a reader might
read dirty data being changed by a writer concurrently, or two writers
might compete writing two distinct messages at the same place in the
ring space.

To address this issue, use a slot-based implementation which
atomically reserves exclusive portions of the ring space readers and
writers will be accessing locklessly. Those slots are guaranteed to
never overlap among read and write requests, until the lockless
operation finishes.

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