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

Tingwei Zhang
2020-08-07T03:52:41Z

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);
> --
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>
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