[PATCH 09/12] perf/core, x86: use test_and_set_bit() to when grabbing a counter

[Robert Richter]

Using test_and_set_bit() in the generic counter allocator makes this
atomic. Otherwise a counter could have been allocated twice.

Signed-off-by: Robert Richter <robert.richter@xxxxxxx>
---
 arch/x86/kernel/cpu/perf_event.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 4eb0355..3f81f91 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1395,8 +1395,13 @@ gen_get_event_idx(struct cpu_hw_events *cpuc, struct hw_perf_event *hwc)
 {
 	int idx;
 
+again:
 	idx = find_first_zero_bit(cpuc->used_mask, x86_pmu.num_counters);
-	return idx == x86_pmu.num_counters ? -1 : idx;
+	if (idx == x86_pmu.num_counters)
+		return -1;
+	if (test_and_set_bit(idx, cpuc->used_mask))
+		goto again;
+	return idx;
 }
 
 /*
@@ -1465,7 +1470,6 @@ try_generic:
 			if (idx == -1)
 				return -EAGAIN;
 
-			set_bit(idx, cpuc->used_mask);
 			hwc->idx = idx;
 		}
 		hwc->config_base = x86_pmu.eventsel;
-- 
1.6.6


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