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

Sai Prakash Ranjan
2020-07-29T05:13:25Z

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);
--
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