Re: [PATCH] coresight: etm4x: Fix etm4_count race using atomic variable

Sai Prakash Ranjan
2020-07-27T14:36:55Z

On 2020-07-27 15:09, Suzuki K Poulose wrote:
> On 07/27/2020 07:07 AM, 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 converting etm4_count variable to atomic.
>>
>> Fixes: 9b6a3f3633a5 ("coresight: etmv4: Fix CPU power management setup
>> in probe() function")
>> Fixes: 58eb457be028 ("hwtracing/coresight-etm4x: Convert to hotplug
>> state machine")
>> Suggested-by: Mike Leach <mike.leach@linaro.org>
>> (Mike: Rootcause and context for commit message)
>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
>
> Please could we leave the hotplug notifier installed with the driver
> init and don't worry about this at all ? We bail out early in the
> notifier anyways, if the CPU is not registered with its ETM.
>

Sure thing, sorry for not taking the cue from earlier discussion.

Thanks,
Sai

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