linux-kernel - [PATCH 5/5] perf/arm_dsu: Fix CPU hotplug races

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Date:   Mon,  4 Feb 2019 17:09:08 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     will.deacon@....com, mark.rutland@....com
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        suzuki.poulose@....com, peterz@...radead.org, tglx@...utronix.de,
        bigeasy@...utronix.de
Subject: [PATCH 5/5] perf/arm_dsu: Fix CPU hotplug races

Like other system PMUs which associate themselves with an arbitrary CPU
for housekeeping purposes, arm_dsu has a race between registering the
hotplug notifier and registering the PMU device, such that the hotplug
niotifier can potentially fire and attempt to migrate the PMU context
before the latter is valid. This is easily resolved by inhibiting
hotplug until both the notifier and PMU device are successfully set up.

For the same reason, also suppress any synchronous notifier calls in the
cleanup path if PMU registration fails.

Signed-off-by: Robin Murphy <robin.murphy@....com>
---
 drivers/perf/arm_dsu_pmu.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/perf/arm_dsu_pmu.c b/drivers/perf/arm_dsu_pmu.c
index 660cb8ac886a..cfaca06b964a 100644
--- a/drivers/perf/arm_dsu_pmu.c
+++ b/drivers/perf/arm_dsu_pmu.c
@@ -717,7 +717,8 @@ static int dsu_pmu_device_probe(struct platform_device *pdev)
 
 	dsu_pmu->irq = irq;
 	platform_set_drvdata(pdev, dsu_pmu);
-	rc = cpuhp_state_add_instance(dsu_pmu_cpuhp_state,
+	cpus_read_lock();
+	rc = cpuhp_state_add_instance_cpuslocked(dsu_pmu_cpuhp_state,
 						&dsu_pmu->cpuhp_node);
 	if (rc)
 		return rc;
@@ -738,9 +739,10 @@ static int dsu_pmu_device_probe(struct platform_device *pdev)
 	};
 
 	rc = perf_pmu_register(&dsu_pmu->pmu, name, -1);
+	cpus_read_unlock();
 	if (rc) {
-		cpuhp_state_remove_instance(dsu_pmu_cpuhp_state,
-						 &dsu_pmu->cpuhp_node);
+		cpuhp_state_remove_instance_nocalls(dsu_pmu_cpuhp_state,
+						    &dsu_pmu->cpuhp_node);
 		irq_set_affinity_hint(dsu_pmu->irq, NULL);
 	}
 
-- 
2.20.1.dirty