tools/perf: Add required memory barriers

To match patch bf378d341e48 ("perf: Fix perf ring buffer memory
ordering") change userspace to also adhere to the ordering outlined.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Michael Neuling <mikey@neuling.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: james.hogan@imgtec.com
Cc: Vince Weaver <vince@deater.net>
Cc: Victor Kaplansky <VICTORK@il.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Anton Blanchard <anton@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Michael Ellerman <michael@ellerman.id.au>
Link: http://lkml.kernel.org/r/20131030104246.GH16117@laptop.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index e99eaed92682..ecaa582f40e2 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -177,7 +177,7 @@ int perf_evlist__strerror_open(struct perf_evlist *evlist, int err, char *buf, s
 static inline unsigned int perf_mmap__read_head(struct perf_mmap *mm)
 {
         struct perf_event_mmap_page *pc = mm->base;
-        int head = pc->data_head;
+        int head = ACCESS_ONCE(pc->data_head);
         rmb();
         return head;
 }
@@ -190,7 +190,7 @@ static inline void perf_mmap__write_tail(struct perf_mmap *md,
         /*
          * ensure all reads are done before we write the tail out.
          */
-        /* mb(); */
+        mb();
         pc->data_tail = tail;
 }