[PATCHv3] coresight: etm4x: Fix etm4_count race by moving cpuhp callbacks to init - CoreSight

29 Jul 2020

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. Also now we can
use non cpuslocked version of cpuhp callbacks with this movement.
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@arm.com
Signed-off-by: Sai Prakash Ranjan saiprakash.ranjan@codeaurora.org
---
Changes in v3:
 * Minor cleanups from v2 and change to device_initcall (Stephen Boyd)
 * Move to non cpuslocked cpuhp callbacks and rename to etm_pm_setup() (Mike Leach)
Changes in v2:
 * Rearrange cpuhp callbacks and move them to driver init (Suzuki K Poulose)
---
 drivers/hwtracing/coresight/coresight-etm4x.c | 65 +++++++++----------
 1 file changed, 31 insertions(+), 34 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c
index 6d7d2169bfb2..fddfd93b9a7b 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,
@@ -1398,28 +1396,25 @@ static struct notifier_block etm4_cpu_pm_nb = {
    .notifier_call = etm4_cpu_pm_notify,
 };
-/* Setup PM. Called with cpus locked. Deals with error conditions and counts */
-static int etm4_pm_setup_cpuslocked(void)
+/* Setup PM. Deals with error conditions and counts */
+static int __init etm4_pm_setup(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",
-						   etm4_starting_cpu, etm4_dying_cpu);
+	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING,
+					"arm/coresight4:starting",
+					etm4_starting_cpu, etm4_dying_cpu);
if (ret)
    	goto unregister_notifier;
-	ret = cpuhp_setup_state_nocalls_cpuslocked(CPUHP_AP_ONLINE_DYN,
-						   "arm/coresight4:online",
-						   etm4_online_cpu, NULL);
+	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+					"arm/coresight4:online",
+					etm4_online_cpu, NULL);
/* HP dyn state ID returned in ret on success */
    if (ret > 0) {
@@ -1428,21 +1423,15 @@ static int etm4_pm_setup_cpuslocked(void)
    }
/* failed dyn state - remove others */
-	cpuhp_remove_state_nocalls_cpuslocked(CPUHP_AP_ARM_CORESIGHT_STARTING);
+	cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING);
unregister_notifier:
    cpu_pm_unregister_notifier(&etm4_cpu_pm_nb);
-
-reduce_count:
-	--etm4_count;
    return ret;
 }
-static void etm4_pm_clear(void)
+static void __init 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 +1576,23 @@ 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;
+
+	ret = etm4_pm_setup();
+
+	/* etm4_pm_setup() does its own cleanup - exit on error */
+	if (ret)
+		return ret;
+
+	ret = amba_driver_register(&etm4x_driver);
+	if (ret) {
+		pr_err("Error registering etm4x driver\n");
+		etm4_pm_clear();
+	}
+
+	return ret;
+}
+device_initcall(etm4x_init);
-- 
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation


    