linux-kernel - [PATCHv2] coresight: etm4x: Fix etm4_count race by moving cpuhp callbacks to init

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Date:   Tue, 28 Jul 2020 13:21:02 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>
Cc:     coresight@...ts.linaro.org, Stephen Boyd <swboyd@...omium.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Subject: [PATCHv2] coresight: etm4x: Fix etm4_count race by moving cpuhp callbacks to init

etm4_count keeps track of number of ETMv4 registered and on some systems,
a race is observed on etm4_count variable which can lead to multiple calls
to cpuhp_setup_state_nocalls_cpuslocked(). This function internally calls
cpuhp_store_callbacks() which prevents multiple registrations of callbacks
for a given state and due to this race, it returns -EBUSY leading to ETM
probe failures like below.

 coresight-etm4x: probe of 7040000.etm failed with error -16

This race can easily be triggered with async probe by setting probe type
as PROBE_PREFER_ASYNCHRONOUS and with ETM power management property
"arm,coresight-loses-context-with-cpu".

Prevent this race by moving cpuhp callbacks to etm driver init since the
cpuhp callbacks doesn't have to depend on the etm4_count and can be once
setup during driver init. Similarly we move cpu_pm notifier registration
to driver init and completely remove etm4_count usage.

Fixes: 9b6a3f3633a5 ("coresight: etmv4: Fix CPU power management setup in probe() function")
Fixes: 58eb457be028 ("hwtracing/coresight-etm4x: Convert to hotplug state machine")
Suggested-by: Suzuki K Poulose <suzuki.poulose@....com>
Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
---

Changes in v2:
 * Rearrange cpuhp callbacks and move them to driver init (Suzuki K Poulose)

---
 drivers/hwtracing/coresight/coresight-etm4x.c | 51 ++++++++++---------
 1 file changed, 27 insertions(+), 24 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c
index 6d7d2169bfb2..adb71987a1e3 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x.c
@@ -48,8 +48,6 @@ module_param(pm_save_enable, int, 0444);
 MODULE_PARM_DESC(pm_save_enable,
 	"Save/restore state on power down: 1 = never, 2 = self-hosted");
 
-/* The number of ETMv4 currently registered */
-static int etm4_count;
 static struct etmv4_drvdata *etmdrvdata[NR_CPUS];
 static void etm4_set_default_config(struct etmv4_config *config);
 static int etm4_set_event_filters(struct etmv4_drvdata *drvdata,
@@ -1403,12 +1401,9 @@ static int etm4_pm_setup_cpuslocked(void)
 {
 	int ret;
 
-	if (etm4_count++)
-		return 0;
-
 	ret = cpu_pm_register_notifier(&etm4_cpu_pm_nb);
 	if (ret)
-		goto reduce_count;
+		return ret;
 
 	ret = cpuhp_setup_state_nocalls_cpuslocked(CPUHP_AP_ARM_CORESIGHT_STARTING,
 						   "arm/coresight4:starting",
@@ -1432,17 +1427,11 @@ static int etm4_pm_setup_cpuslocked(void)
 
 unregister_notifier:
 	cpu_pm_unregister_notifier(&etm4_cpu_pm_nb);
-
-reduce_count:
-	--etm4_count;
 	return ret;
 }
 
 static void etm4_pm_clear(void)
 {
-	if (--etm4_count != 0)
-		return;
-
 	cpu_pm_unregister_notifier(&etm4_cpu_pm_nb);
 	cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING);
 	if (hp_online) {
@@ -1498,22 +1487,12 @@ static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
 	if (!desc.name)
 		return -ENOMEM;
 
-	cpus_read_lock();
 	etmdrvdata[drvdata->cpu] = drvdata;
 
 	if (smp_call_function_single(drvdata->cpu,
 				etm4_init_arch_data,  drvdata, 1))
 		dev_err(dev, "ETM arch init failed\n");
 
-	ret = etm4_pm_setup_cpuslocked();
-	cpus_read_unlock();
-
-	/* etm4_pm_setup_cpuslocked() does its own cleanup - exit on error */
-	if (ret) {
-		etmdrvdata[drvdata->cpu] = NULL;
-		return ret;
-	}
-
 	if (etm4_arch_supported(drvdata->arch) == false) {
 		ret = -EINVAL;
 		goto err_arch_supported;
@@ -1560,7 +1539,6 @@ static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
 
 err_arch_supported:
 	etmdrvdata[drvdata->cpu] = NULL;
-	etm4_pm_clear();
 	return ret;
 }
 
@@ -1598,4 +1576,29 @@ static struct amba_driver etm4x_driver = {
 	.probe		= etm4_probe,
 	.id_table	= etm4_ids,
 };
-builtin_amba_driver(etm4x_driver);
+
+static int __init etm4x_init(void)
+{
+	int ret;
+
+	cpus_read_lock();
+	ret = etm4_pm_setup_cpuslocked();
+	cpus_read_unlock();
+
+	/* etm4_pm_setup_cpuslocked() does its own cleanup - exit on error */
+	if (ret)
+		return ret;
+
+	ret = amba_driver_register(&etm4x_driver);
+	if (ret) {
+		pr_info("Error registering etm4x driver\n");
+		goto err_init;
+	}
+
+	return ret;
+
+err_init:
+	etm4_pm_clear();
+	return ret;
+}
+module_init(etm4x_init);
-- 
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