perf_event: Make software events work again

Commit 6bde9b6c ("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

@@ -664,14 +664,14 @@ group_sched_in(struct perf_event *group_event,
 		}
 	}
 
-	if (txn) {
+	if (!txn)
+		return 0;
+
 	ret = pmu->commit_txn(pmu);
 	if (!ret) {
 		pmu->cancel_txn(pmu);
-
 		return 0;
 	}
-	}
 
 group_error:
 	if (txn)