tracepoint_probe_unregister() does not synchronize against the probe
callbacks, so do that explicitly. This properly serializes the callbacks
and the free of the data used therein.

Also, use this_cpu_ptr() where possible.
Acked-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1274438476.1674.1702.camel@laptop>
Signed-off-by: NIngo Molnar <mingo@elte.hu>