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

[Tingwei Zhang]

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@xxxxxxx>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> ---
> 
> 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);
> -- 
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