[PATCH v11 18/27] coresight: Save active path for system tracers

[Leo Yan]

This commit only set the path pointer for system tracers (e.g. STM) in
coresight_{enable|disable}_source().

Later changes will set the path pointer locally for per-CPU sources.
This is because the mode and path pointer must be set together, so that
they are observed atomically by the CPU PM notifier.

Signed-off-by: Leo Yan <leo.yan at arm.com>
---
 drivers/hwtracing/coresight/coresight-core.c | 23 ++++++++++++++++++++++-
 include/linux/coresight.h                    |  2 ++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index 308282d2d4611997834bd39dc2de271bfa568ee0..b45fb38eb9d652e44802c23ea4ee3b051d635207 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -478,10 +478,28 @@ int coresight_enable_source(struct coresight_device *csdev,
 			    struct perf_event *event, enum cs_mode mode,
 			    struct coresight_path *path)
 {
+	int ret;
+
 	if (!coresight_is_device_source(csdev))
 		return -EINVAL;
 
-	return source_ops(csdev)->enable(csdev, event, mode, path);
+	ret = source_ops(csdev)->enable(csdev, event, mode, path);
+	if (ret)
+		return ret;
+
+	/*
+	 * Update the path pointer until after the source is enabled to avoid
+	 * races where multiple paths attempt to enable the same source.
+	 *
+	 * Do not set the path pointer here for per-CPU sources; set it locally
+	 * on the CPU instead. Otherwise, there is a window where the path is
+	 * enabled but the pointer is not yet set, causing CPU PM notifiers to
+	 * miss PM operations due to reading a NULL pointer.
+	 */
+	if (!coresight_is_percpu_source(csdev))
+		csdev->path = path;
+
+	return 0;
 }
 
 void coresight_disable_source(struct coresight_device *csdev, void *data)
@@ -489,6 +507,9 @@ void coresight_disable_source(struct coresight_device *csdev, void *data)
 	if (!coresight_is_device_source(csdev))
 		return;
 
+	if (!coresight_is_percpu_source(csdev))
+		csdev->path = NULL;
+
 	source_ops(csdev)->disable(csdev, data);
 }
 EXPORT_SYMBOL_GPL(coresight_disable_source);
diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index 5f9d7ea9f5941ab01eb6a084ca558a9417c7727f..58d474b269806d32cad6ed87da96550b06f1f30f 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -257,6 +257,7 @@ struct coresight_trace_id_map {
  *		by @coresight_ops.
  * @access:	Device i/o access abstraction for this device.
  * @dev:	The device entity associated to this component.
+ * @path:	Activated path pointer (only used for source device).
  * @mode:	The device mode, i.e sysFS, Perf or disabled. This is actually
  *		an 'enum cs_mode' but stored in an atomic type. Access is always
  *		through atomic APIs, ensuring SMP-safe synchronisation between
@@ -291,6 +292,7 @@ struct coresight_device {
 	const struct coresight_ops *ops;
 	struct csdev_access access;
 	struct device dev;
+	struct coresight_path *path;
 	atomic_t mode;
 	int refcnt;
 	int cpu;

-- 
2.34.1