On Wed, Aug 05, 2020 at 06:55:40PM +0800, Suzuki K Poulose wrote:

On 08/05/2020 03:54 AM, Tingwei Zhang wrote:

quoted

When coresight device is in an active session, driver module of
that device should not be removed. Use try_get_module() in
coresight_grab_device() to prevent module to be unloaded.
Use get_device()/put_device() to protect device data
in the middle of active session.

Signed-off-by: Tingwei Zhang <redacted>
Tested-by: Mike Leach <redacted>
---
 drivers/hwtracing/coresight/coresight.c | 39 +++++++++++++++++++++----
 1 file changed, 34 insertions(+), 5 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight.c

b/drivers/hwtracing/coresight/coresight.c

quoted

index b7151c5f81b1..1626bc885dfe 100644

--- a/drivers/hwtracing/coresight/coresight.c
+++ b/drivers/hwtracing/coresight/coresight.c

@@ -640,7 +640,7 @@ struct coresight_device

*coresight_get_sink_by_id(u32 id)

quoted

  * don't appear on the trace path, they should be handled along with

the

quoted

  * the master device.
  */
-static void coresight_grab_device(struct coresight_device *csdev)
+static int coresight_grab_device(struct coresight_device *csdev)
 {
 	int i;

Please could you add a pair of helper functions to hold/drop reference
to a device/driver ? i.e,

static inline bool coresight_get_ref(struct coresight_device *csdev)
{
	struct device *dev = csdev->dev.parent;

	/* Make sure the driver cant be removed */
	if (!try_module_get(dev->driver->owner))
		return false;
	/* Make sure the device can't go away */
	get_device(dev);
	pm_runtime_get_sync(dev);
	return true;
}

Sure. I'll add it to next revision.

Thanks,
Tingwei 

static inline void coresight_put_ref(struct coresight_device *csdev)
{
	struct device *dev = csdev->dev.parent;

	pm_runtime_put(dev);
	put_device(dev);
	module_put(dev->driver->owner);
}

quoted

@@ -648,10 +648,30 @@ static void coresight_grab_device(struct

coresight_device *csdev)

quoted

 		struct coresight_device *child;
 		child  = csdev->pdata->conns[i].child_dev;
-		if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
+		if (child && child->type == CORESIGHT_DEV_TYPE_HELPER) {
+			if

(!try_module_get(child->dev.parent->driver->owner))

quoted

+				goto err;
+			get_device(child->dev.parent);
 			pm_runtime_get_sync(child->dev.parent);
+		}
 	}

This could then be :
		if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
			if (!coresight_get_ref(child))
				goto err;

quoted

+	if (!try_module_get(csdev->dev.parent->driver->owner))
+		goto err;
+	get_device(csdev->dev.parent);
 	pm_runtime_get_sync(csdev->dev.parent);

	if (coresight_get_ref(csdev))
		return 0;

quoted

+	return 0;
+err:
+	for (i--; i >= 0; i--) {
+		struct coresight_device *child;
+
+		child  = csdev->pdata->conns[i].child_dev;
+		if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
+			pm_runtime_put(child->dev.parent);
+			put_device(child->dev.parent);
+			module_put(child->dev.parent->driver->owner);
+		}

And this could be :

		if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
			coresight_put_ref(child);

quoted

+	}
+	return -ENODEV;
 }
 /*

@@ -663,12 +683,17 @@ static void coresight_drop_device(struct

coresight_device *csdev)

quoted

 	int i;
 	pm_runtime_put(csdev->dev.parent);
+	put_device(csdev->dev.parent);
+	module_put(csdev->dev.parent->driver->owner);

	coresight_put_ref(csdev);

quoted

 	for (i = 0; i < csdev->pdata->nr_outport; i++) {
 		struct coresight_device *child;
 		child  = csdev->pdata->conns[i].child_dev;
-		if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
+		if (child && child->type == CORESIGHT_DEV_TYPE_HELPER) {
 			pm_runtime_put(child->dev.parent);
+			put_device(child->dev.parent);
+			module_put(child->dev.parent->driver->owner);
+		}

	coresight_put_ref(child);

quoted

 	}
 }

@@ -687,7 +712,7 @@ static int _coresight_build_path(struct

coresight_device *csdev,

quoted

 				 struct coresight_device *sink,
 				 struct list_head *path)
 {
-	int i;
+	int i, ret;
 	bool found = false;
 	struct coresight_node *node;

@@ -721,7 +746,11 @@ static int _coresight_build_path(struct

coresight_device *csdev,

quoted

 	if (!node)
 		return -ENOMEM;
-	coresight_grab_device(csdev);
+	ret = coresight_grab_device(csdev);
+	if (ret) {
+		kfree(node);
+		return ret;
+	}
 	node->csdev = csdev;
 	list_add(&node->link, path);

Cheers
Suzuki

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