perf: Ensure that IOC_OUTPUT isn't used to create multi-writer buffers

perf: Ensure that IOC_OUTPUT isn't used to create multi-writer buffers

Since we want to ensure buffers only have a single
writer, we must avoid creating one with multiple.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20100521090710.528215873@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>