Hi Sai,
On Tue, 28 Jul 2020 at 08:51, Sai Prakash Ranjan saiprakash.ranjan@codeaurora.org wrote:
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@arm.com Signed-off-by: Sai Prakash Ranjan saiprakash.ranjan@codeaurora.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) {
consider renaming this to etm4_pm_setup() and handing any cpu locking inside the function. In the circumstances - as part of the driver init rather than probe it may be sufficient to call the cpuhp_setup functions without the _cpuslocked suffix and allow the calls to lock the cpus as they are made. i.e. cpuhp_setup_state_nocalls_cpuslocked() => cpuhp_setup_state_nocalls()
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();
See my comment above about rename and use of cpus_read_lock
Regards
Mike
/* 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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