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Message-ID: <08767949db1c9e142d29e8d3ab16bd1f@codeaurora.org>
Date: Wed, 29 Jul 2020 10:33:58 +0530
From: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To: Mike Leach <mike.leach@...aro.org>
Cc: Mathieu Poirier <mathieu.poirier@...aro.org>,
Suzuki K Poulose <suzuki.poulose@....com>,
linux-arm-msm@...r.kernel.org,
Coresight ML <coresight@...ts.linaro.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Stephen Boyd <swboyd@...omium.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCHv2] coresight: etm4x: Fix etm4_count race by moving cpuhp
callbacks to init
Hi Mike,
On 2020-07-29 01:46, Mike Leach wrote:
> Hi Sai,
>
> On Tue, 28 Jul 2020 at 08:51, Sai Prakash Ranjan
> <saiprakash.ranjan@...eaurora.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@....com>
>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.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()
Sure, will make this change.
>
>> 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
>
Yes, thanks for the review Mike.
Thanks,
Sai
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