[PATCH v2 06/24] perf: Fix pmus_lock vs pmus_srcu ordering

[Peter Zijlstra]

Commit a63fbed776c7 ("perf/tracing/cpuhotplug: Fix locking order")
placed pmus_lock inside pmus_srcu, this makes perf_pmu_unregister()
trip lockdep.

Move the locking about such that only pmu_idr and pmus (list) are
modified while holding pmus_lock. This avoids doing synchronize_srcu()
while holding pmus_lock and all is well again.

Fixes: a63fbed776c7 ("perf/tracing/cpuhotplug: Fix locking order")
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/events/core.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11836,6 +11836,8 @@ void perf_pmu_unregister(struct pmu *pmu
 {
 	mutex_lock(&pmus_lock);
 	list_del_rcu(&pmu->entry);
+	idr_remove(&pmu_idr, pmu->type);
+	mutex_unlock(&pmus_lock);
 
 	/*
 	 * We dereference the pmu list under both SRCU and regular RCU, so
@@ -11845,7 +11847,6 @@ void perf_pmu_unregister(struct pmu *pmu
 	synchronize_rcu();
 
 	free_percpu(pmu->pmu_disable_count);
-	idr_remove(&pmu_idr, pmu->type);
 	if (pmu_bus_running && pmu->dev && pmu->dev != PMU_NULL_DEV) {
 		if (pmu->nr_addr_filters)
 			device_remove_file(pmu->dev, &dev_attr_nr_addr_filters);
@@ -11853,7 +11854,6 @@ void perf_pmu_unregister(struct pmu *pmu
 		put_device(pmu->dev);
 	}
 	free_pmu_context(pmu);
-	mutex_unlock(&pmus_lock);
 }
 EXPORT_SYMBOL_GPL(perf_pmu_unregister);