[RFC 05/10] perf/arm-dsu: Make dsu_pmu_cpu_teardown() parallel

[Pingfan Liu]

In the case of kexec quick reboot, dsu_pmu_cpu_teardown() confronts
parallel and lock are needed to protect the contest on a dsu_pmu.

Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
To: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
To: linux-kernel@xxxxxxxxxxxxxxx
---
 drivers/perf/arm_dsu_pmu.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/perf/arm_dsu_pmu.c b/drivers/perf/arm_dsu_pmu.c
index a36698a90d2f..aa9f4393ff0c 100644
--- a/drivers/perf/arm_dsu_pmu.c
+++ b/drivers/perf/arm_dsu_pmu.c
@@ -833,16 +833,23 @@ static int dsu_pmu_cpu_teardown(unsigned int cpu, struct hlist_node *node)
 	struct dsu_pmu *dsu_pmu = hlist_entry_safe(node, struct dsu_pmu,
 						   cpuhp_node);
 
-	if (!cpumask_test_and_clear_cpu(cpu, &dsu_pmu->active_cpu))
+	raw_spin_lock(&dsu_pmu->pmu_lock);
+	if (!cpumask_test_and_clear_cpu(cpu, &dsu_pmu->active_cpu)) {
+		raw_spin_unlock(&dsu_pmu->pmu_lock);
 		return 0;
+	}
 
 	dst = dsu_pmu_get_online_cpu_any_but(dsu_pmu, cpu);
 	/* If there are no active CPUs in the DSU, leave IRQ disabled */
-	if (dst >= nr_cpu_ids)
+	if (dst >= nr_cpu_ids) {
+		raw_spin_unlock(&dsu_pmu->pmu_lock);
 		return 0;
+	}
 
-	perf_pmu_migrate_context(&dsu_pmu->pmu, cpu, dst);
+	/* dst should not be in dying mask. So after setting, blocking parallel */
 	dsu_pmu_set_active_cpu(dst, dsu_pmu);
+	raw_spin_unlock(&dsu_pmu->pmu_lock);
+	perf_pmu_migrate_context(&dsu_pmu->pmu, cpu, dst);
 
 	return 0;
 }
@@ -858,6 +865,7 @@ static int __init dsu_pmu_init(void)
 	if (ret < 0)
 		return ret;
 	dsu_pmu_cpuhp_state = ret;
+	cpuhp_set_step_parallel(ret);
 	return platform_driver_register(&dsu_pmu_driver);
 }
 
-- 
2.31.1