perf_counter: Fix throttling lock-up

Throttling logic is broken and we can lock up with too small
hw sampling intervals.

Make the throttling code more robust: disable counters even
if we already disabled them.

( Also clean up whitespace damage i noticed while reading
  various pieces of code related to throttling. )

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/cpu/perf_counter.c

@@ -91,7 +91,7 @@ static u64 intel_pmu_raw_event(u64 event)
 #define CORE_EVNTSEL_INV_MASK		0x00800000ULL
 #define CORE_EVNTSEL_COUNTER_MASK	0xFF000000ULL
 
-#define CORE_EVNTSEL_MASK 		\
+#define CORE_EVNTSEL_MASK		\
 	(CORE_EVNTSEL_EVENT_MASK |	\
 	 CORE_EVNTSEL_UNIT_MASK  |	\
 	 CORE_EVNTSEL_EDGE_MASK  |	\

kernel/perf_counter.c

@@ -2822,11 +2822,20 @@ int perf_counter_overflow(struct perf_counter *counter,
 
 	if (!throttle) {
 		counter->hw.interrupts++;
-	} else if (counter->hw.interrupts != MAX_INTERRUPTS) {
-		counter->hw.interrupts++;
-		if (HZ*counter->hw.interrupts > (u64)sysctl_perf_counter_limit) {
-			counter->hw.interrupts = MAX_INTERRUPTS;
-			perf_log_throttle(counter, 0);
+	} else {
+		if (counter->hw.interrupts != MAX_INTERRUPTS) {
+			counter->hw.interrupts++;
+			if (HZ*counter->hw.interrupts > (u64)sysctl_perf_counter_limit) {
+				counter->hw.interrupts = MAX_INTERRUPTS;
+				perf_log_throttle(counter, 0);
+				ret = 1;
+			}
+		} else {
+			/*
+			 * Keep re-disabling counters even though on the previous
+			 * pass we disabled it - just in case we raced with a
+			 * sched-in and the counter got enabled again:
+			 */
 			ret = 1;
 		}
 	}