coresight: Take hotplug lock in enable_source_store() for Sysfs mode

The hotplug lock is acquired and released in etm{3|4}_disable_sysfs(),
which are low-level functions.  This prevents us from a new solution for
hotplug.

Firstly, hotplug callbacks cannot invoke etm{3|4}_disable_sysfs() to
disable the source; otherwise, a deadlock issue occurs.  The reason is
that, in the hotplug flow, the kernel acquires the hotplug lock before
calling callbacks.  Subsequently, if coresight_disable_source() is
invoked and it calls etm{3|4}_disable_sysfs(), the hotplug lock will be
acquired twice, leading to a double lock issue.

Secondly, when hotplugging a CPU on or off, if we want to manipulate all
components on a path attached to the CPU, we need to maintain atomicity
for the entire path.  Otherwise, a race condition may occur with users
setting the same path via the Sysfs knobs, ultimately causing mess
states in CoreSight components.

This patch moves the hotplug locking from etm{3|4}_disable_sysfs() into
enable_source_store().  As a result, when users control the Sysfs knobs,
the whole flow is protected by hotplug locking, ensuring it is mutual
exclusive with hotplug callbacks.

Note, the paired function etm{3|4}_enable_sysfs() does not use hotplug
locking, which is why this patch does not modify it.

Reviewed-by: Mike Leach <mike.leach@linaro.org>
Tested-by: James Clark <james.clark@linaro.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Tested-by: Jie Gan <jie.gan@oss.qualcomm.com>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20260515-arm_coresight_path_power_management_improvement-v14-6-f88c4a3ecfe9@arm.com

diff --git a/drivers/hwtracing/coresight/coresight-etm3x-core.c b/drivers/hwtracing/coresight/coresight-etm3x-core.c
index ab47f69e923fb191b48b82367dce465c79b3a93d..aeeb284abdbe4b6a0960da45baa1138e203f3e3c 100644 (file)
--- a/drivers/hwtracing/coresight/coresight-etm3x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c
@@ -620,13 +620,6 @@ static void etm_disable_sysfs(struct coresight_device *csdev)
 {
        struct etm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 
-       /*
-        * Taking hotplug lock here protects from clocks getting disabled
-        * with tracing being left on (crash scenario) if user disable occurs
-        * after cpu online mask indicates the cpu is offline but before the
-        * DYING hotplug callback is serviced by the ETM driver.
-        */
-       cpus_read_lock();
        spin_lock(&drvdata->spinlock);
 
        /*
@@ -637,7 +630,6 @@ static void etm_disable_sysfs(struct coresight_device *csdev)
                                 drvdata, 1);
 
        spin_unlock(&drvdata->spinlock);
-       cpus_read_unlock();
 
        /*
         * we only release trace IDs when resetting sysfs.

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index b7312570a7ae1f0355c01b6f7a54ea2dd8891097..7011a20d20042cfbeaac51797cd8592275bbf1ca 100644 (file)
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -1110,13 +1110,6 @@ static void etm4_disable_sysfs(struct coresight_device *csdev)
 {
        struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 
-       /*
-        * Taking hotplug lock here protects from clocks getting disabled
-        * with tracing being left on (crash scenario) if user disable occurs
-        * after cpu online mask indicates the cpu is offline but before the
-        * DYING hotplug callback is serviced by the ETM driver.
-        */
-       cpus_read_lock();
        raw_spin_lock(&drvdata->spinlock);
 
        /*
@@ -1130,8 +1123,6 @@ static void etm4_disable_sysfs(struct coresight_device *csdev)
 
        cscfg_csdev_disable_active_config(csdev);
 
-       cpus_read_unlock();
-
        /*
         * we only release trace IDs when resetting sysfs.
         * This permits sysfs users to read the trace ID after the trace

diff --git a/drivers/hwtracing/coresight/coresight-sysfs.c b/drivers/hwtracing/coresight/coresight-sysfs.c
index 905c973e99cea884e242eab460b31544c49378ad..682500b7296c20453edd0290e1dc44124e0c3228 100644 (file)
--- a/drivers/hwtracing/coresight/coresight-sysfs.c
+++ b/drivers/hwtracing/coresight/coresight-sysfs.c
@@ -362,6 +362,13 @@ static ssize_t enable_source_store(struct device *dev,
        if (ret)
                return ret;
 
+       /*
+        * CoreSight hotplug callbacks in core layer control a activated path
+        * from its source to sink. Taking hotplug lock here protects a race
+        * condition with hotplug callbacks.
+        */
+       guard(cpus_read_lock)();
+
        if (val) {
                ret = coresight_enable_sysfs(csdev);
                if (ret)