Messages in this thread | | | Subject | Re: [PATCH] coresight: etm4x: Fix etm4_count race using atomic variable | From | Suzuki K Poulose <> | Date | Mon, 27 Jul 2020 10:39:43 +0100 |
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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.
Cheers Suzuki
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