[PATCH] powercap: intel_rapl: Fix kernel panic during PMU unbind

[Sumeet Pawnikar <sumeet4linux@gmail.com>]

rapl_package_add_pmu() fails internally at perf_pmu_register(),
and rapl_pmu_update() leaves the global rapl_pmu.pmu structure
zero-initialized via memset and returns an error. But any
previously probed packages retain has_pmu = true.

When the driver is subsequently unbound or removed,
rapl_package_remove_pmu_locked() sees has_pmu == true and
unconditionally calls perf_pmu_unregister(&rapl_pmu.pmu) on the
zeroed-out structure. This attempts a list_del_rcu() on a NULL
list head, immediately causing a kernel panic.

Fix this by checking if the PMU is actually registered before
attempting to unregister it.

Signed-off-by: Sumeet Pawnikar <sumeet4linux@gmail.com>
---
 drivers/powercap/intel_rapl_common.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/powercap/intel_rapl_common.c b/drivers/powercap/intel_rapl_common.c
index 1006d183d508..22100f1ca222 100644
--- a/drivers/powercap/intel_rapl_common.c
+++ b/drivers/powercap/intel_rapl_common.c
@@ -1652,7 +1652,8 @@ void rapl_package_remove_pmu_locked(struct rapl_package *rp)
 			return;
 	}
 
-	perf_pmu_unregister(&rapl_pmu.pmu);
+	if (rapl_pmu.registered)
+		perf_pmu_unregister(&rapl_pmu.pmu);
 	memset(&rapl_pmu, 0, sizeof(struct rapl_pmu));
 }
 EXPORT_SYMBOL_NS_GPL(rapl_package_remove_pmu_locked, "INTEL_RAPL");
-- 
2.43.0