Messages in this thread | | | Date | Wed, 29 Jul 2020 10:33:58 +0530 | From | Sai Prakash Ranjan <> | Subject | Re: [PATCHv2] coresight: etm4x: Fix etm4_count race by moving cpuhp callbacks to init |
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Hi Mike,
On 2020-07-29 01:46, Mike Leach wrote: > Hi Sai, > > On Tue, 28 Jul 2020 at 08:51, Sai Prakash Ranjan > <saiprakash.ranjan@codeaurora.org> 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 moving cpuhp callbacks to etm driver init since >> the >> cpuhp callbacks doesn't have to depend on the etm4_count and can be >> once >> setup during driver init. Similarly we move cpu_pm notifier >> registration >> to driver init and completely remove etm4_count usage. >> >> Fixes: 9b6a3f3633a5 ("coresight: etmv4: Fix CPU power management setup >> in probe() function") >> Fixes: 58eb457be028 ("hwtracing/coresight-etm4x: Convert to hotplug >> state machine") >> Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com> >> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org> >> --- >> >> Changes in v2: >> * Rearrange cpuhp callbacks and move them to driver init (Suzuki K >> Poulose) >> >> --- >> drivers/hwtracing/coresight/coresight-etm4x.c | 51 >> ++++++++++--------- >> 1 file changed, 27 insertions(+), 24 deletions(-) >> >> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c >> b/drivers/hwtracing/coresight/coresight-etm4x.c >> index 6d7d2169bfb2..adb71987a1e3 100644 >> --- a/drivers/hwtracing/coresight/coresight-etm4x.c >> +++ b/drivers/hwtracing/coresight/coresight-etm4x.c >> @@ -48,8 +48,6 @@ module_param(pm_save_enable, int, 0444); >> 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 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, >> @@ -1403,12 +1401,9 @@ static int etm4_pm_setup_cpuslocked(void) >> { > > consider renaming this to etm4_pm_setup() and handing any cpu locking > inside the function. > In the circumstances - as part of the driver init rather than probe it > may be sufficient to call the cpuhp_setup functions without the > _cpuslocked suffix and allow the calls to lock the cpus as they are > made. > i.e. cpuhp_setup_state_nocalls_cpuslocked() => > cpuhp_setup_state_nocalls()
Sure, will make this change.
> >> int ret; >> >> - if (etm4_count++) >> - return 0; >> - >> ret = cpu_pm_register_notifier(&etm4_cpu_pm_nb); >> if (ret) >> - goto reduce_count; >> + return ret; >> >> ret = >> cpuhp_setup_state_nocalls_cpuslocked(CPUHP_AP_ARM_CORESIGHT_STARTING, >> >> "arm/coresight4:starting", >> @@ -1432,17 +1427,11 @@ static int etm4_pm_setup_cpuslocked(void) >> >> unregister_notifier: >> cpu_pm_unregister_notifier(&etm4_cpu_pm_nb); >> - >> -reduce_count: >> - --etm4_count; >> return ret; >> } >> >> static void etm4_pm_clear(void) >> { >> - if (--etm4_count != 0) >> - return; >> - >> cpu_pm_unregister_notifier(&etm4_cpu_pm_nb); >> cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING); >> if (hp_online) { >> @@ -1498,22 +1487,12 @@ static int etm4_probe(struct amba_device >> *adev, const struct amba_id *id) >> if (!desc.name) >> return -ENOMEM; >> >> - cpus_read_lock(); >> etmdrvdata[drvdata->cpu] = drvdata; >> >> if (smp_call_function_single(drvdata->cpu, >> etm4_init_arch_data, drvdata, 1)) >> dev_err(dev, "ETM arch init failed\n"); >> >> - ret = etm4_pm_setup_cpuslocked(); >> - cpus_read_unlock(); >> - >> - /* etm4_pm_setup_cpuslocked() does its own cleanup - exit on >> error */ >> - if (ret) { >> - etmdrvdata[drvdata->cpu] = NULL; >> - return ret; >> - } >> - >> if (etm4_arch_supported(drvdata->arch) == false) { >> ret = -EINVAL; >> goto err_arch_supported; >> @@ -1560,7 +1539,6 @@ static int etm4_probe(struct amba_device *adev, >> const struct amba_id *id) >> >> err_arch_supported: >> etmdrvdata[drvdata->cpu] = NULL; >> - etm4_pm_clear(); >> return ret; >> } >> >> @@ -1598,4 +1576,29 @@ static struct amba_driver etm4x_driver = { >> .probe = etm4_probe, >> .id_table = etm4_ids, >> }; >> -builtin_amba_driver(etm4x_driver); >> + >> +static int __init etm4x_init(void) >> +{ >> + int ret; >> + >> + cpus_read_lock(); >> + ret = etm4_pm_setup_cpuslocked(); >> + cpus_read_unlock(); > > See my comment above about rename and use of cpus_read_lock >
Yes, thanks for the review Mike.
Thanks, Sai
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