perf_event: Make software events work again

Commit 6bde9b6ce0127e2a56228a2071536d422be31336 ("perf: Add
group scheduling transactional APIs") added code to allow a
group to be scheduled in a single transaction.  However, it
introduced a bug in handling events whose pmu does not implement
transactions -- at the end of scheduling in the events in the
group, in the non-transactional case the code now falls through
to the group_error label, and proceeds to unschedule all the
events in the group and return failure.

This fixes it by returning 0 (success) in the non-transactional
case.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Lin Ming <ming.m.lin@intel.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: eranian@gmail.com
LKML-Reference: <20100508105800.GB10650@brick.ozlabs.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/perf_event.c

@@ -664,13 +664,13 @@ group_sched_in(struct perf_event *group_event,
 		}
 	}
 
-	if (txn) {
-		ret = pmu->commit_txn(pmu);
-		if (!ret) {
-			pmu->cancel_txn(pmu);
+	if (!txn)
+		return 0;
 
-			return 0;
-		}
+	ret = pmu->commit_txn(pmu);
+	if (!ret) {
+		pmu->cancel_txn(pmu);
+		return 0;
 	}
 
 group_error: