[PATCH v6 08/13] coresight: etm4x: remove redundant call etm4_enable_hw() with hotplug

Yeoreum Yun
2026-04-22T13:22:43Z

The cpu_online_mask is set at the CPUHP_BRINGUP_CPU step.
In other words, if etm4_enable_sysfs() is called between
CPUHP_BRINGUP_CPU and CPUHP_AP_ARM_CORESIGHT_STARTING,
etm4_enable_hw() may be invoked in etm4_enable_sysfs_smp_call()
and then executed again in etm4_starting_cpu().

To remove this redundant call, take the hotplug lock before executing
etm4_enable_sysfs_smp_call().

Reviewed-by: Jie Gan <jie.gan@oss.qualcomm.com>
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
drivers/hwtracing/coresight/coresight-etm4x-core.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 5c74e3d63dcd..66d09e0a4171 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -962,8 +962,20 @@ static int etm4_enable_sysfs(struct coresight_device *csdev, struct coresight_pa
arg.config = drvdata->config;
raw_spin_unlock(&drvdata->spinlock);

+ /*
+ * Take the hotplug lock to prevent redundant calls to etm4_enable_hw().
+ *
+ * The cpu_online_mask is set at the CPUHP_BRINGUP_CPU step.
+ * In other words, if etm4_enable_sysfs() is called between
+ * CPUHP_BRINGUP_CPU and CPUHP_AP_ARM_CORESIGHT_STARTING,
+ * etm4_enable_hw() may be invoked in etm4_enable_sysfs_smp_call()
+ * and then executed again in etm4_starting_cpu().
+ */
+ cpus_read_lock();
ret = smp_call_function_single(drvdata->cpu,
etm4_enable_sysfs_smp_call, &arg, 1);
+ cpus_read_unlock();
+
if (!ret)
ret = arg.rc;
if (!ret)