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 --- drivers/hwtracing/coresight/coresight-etm4x.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c index 6d7d2169bfb2..f256ea744c51 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x.c +++ b/drivers/hwtracing/coresight/coresight-etm4x.c @@ -49,7 +49,7 @@ 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 atomic_t 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, @@ -1403,7 +1403,7 @@ static int etm4_pm_setup_cpuslocked(void) { int ret;

- if (etm4_count++) + if (atomic_inc_return(&etm4_count)) return 0;

ret = cpu_pm_register_notifier(&etm4_cpu_pm_nb); @@ -1434,13 +1434,13 @@ static int etm4_pm_setup_cpuslocked(void) cpu_pm_unregister_notifier(&etm4_cpu_pm_nb);

reduce_count: - --etm4_count; + atomic_dec(&etm4_count); return ret; }

static void etm4_pm_clear(void) { - if (--etm4_count != 0) + if (atomic_dec_return(&etm4_count) != 0) return;

cpu_pm_unregister_notifier(&etm4_cpu_pm_nb);