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@xxxxxxxxxxxxxx> 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@xxxxxxx>
Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
---
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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