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