| Message ID | 20200727060728.15027-1-saiprakash.ranjan@codeaurora.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | coresight: etm4x: Fix etm4_count race using atomic variable | expand |
On 2020-07-27 11:37, 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> > --- > 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; > Sorry, I messed up here, will send a next version fixing this. Thanks, Sai
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
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
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);
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(-)