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

tingwei
2020-08-07T03:58:56Z

Sorry for the noise. Please ignore previous comment.
The change is in old patch set of my series.
This change is good to go.
On 2020-08-07 11:52, Tingwei Zhang wrote:
> On Wed, Jul 29, 2020 at 01:13:10PM +0800, Sai Prakash Ranjan 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. 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() is called in etm4x_init(), but etm4_pm_clear() is
> called
> in etm4_remove(). If one ETM4x device is removed, etm4_remove() would
> be
> called and we could still have other ETM4x device alive.
>
> Should etm4_pm_clear() be called in etm4x_exit()? It should only be
> called
> when module exits.
>
> Thanks,
> Tingwei
>
>> +
>> + /* 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
>>
>> _______________________________________________
>> CoreSight mailing list
>> CoreSight@lists.linaro.org
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>
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