[patch V2 28/29] lockup_detector/perf: Simplify deferred event destroy

[Thomas Gleixner]

Now that all functionality is properly serialized against CPU hotplug,
remove the extra per cpu storage which holds the disabled events for
cleanup. The core makes sure that cleanup happens before new events are
created.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Don Zickus <dzickus@xxxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Sebastian Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Ulrich Obergfell <uobergfe@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20170831073055.251195167@xxxxxxxxxxxxx

---
 kernel/watchdog_hld.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

--- a/kernel/watchdog_hld.c
+++ b/kernel/watchdog_hld.c
@@ -21,7 +21,6 @@
 static DEFINE_PER_CPU(bool, hard_watchdog_warn);
 static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
-static DEFINE_PER_CPU(struct perf_event *, dead_event);
 static struct cpumask dead_events_mask;
 
 static unsigned long hardlockup_allcpu_dumped;
@@ -204,8 +203,6 @@ void hardlockup_detector_perf_disable(vo
 
 	if (event) {
 		perf_event_disable(event);
-		this_cpu_write(watchdog_ev, NULL);
-		this_cpu_write(dead_event, event);
 		cpumask_set_cpu(smp_processor_id(), &dead_events_mask);
 		watchdog_cpus--;
 	}
@@ -221,9 +218,9 @@ void hardlockup_detector_perf_cleanup(vo
 	int cpu;
 
 	for_each_cpu(cpu, &dead_events_mask) {
-		struct perf_event *event = per_cpu(dead_event, cpu);
+		struct perf_event *event = per_cpu(watchdog_ev, cpu);
 
-		per_cpu(dead_event, cpu) = NULL;
+		per_cpu(watchdog_ev, cpu) = NULL;
 		perf_event_release_kernel(event);
 	}
 	cpumask_clear(&dead_events_mask);