Re: [PATCH v2] coresight: core: Fix coresight device probe failure issue

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Hi Jinlong

On 04/03/2022 08:23, Mao Jinlong wrote:
It is possibe that probe failure issue happens when the device
and its child_device's probe happens at the same time.
In coresight_make_links, has_conns_grp is true for parent, but
has_conns_grp is false for child device as has_conns_grp is set
to true in coresight_create_conns_sysfs_group. The probe of parent
device will fail at this condition. Add has_conns_grp check for
child device before make the links and make the process from
device_register to connection_create be atomic to avoid this
probe failure issue.

Suggested-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Suggested-by: Mike Leach <mike.leach@xxxxxxxxxx>
Signed-off-by: Mao Jinlong <quic_jinlmao@xxxxxxxxxxx>
---
  drivers/hwtracing/coresight/coresight-core.c | 12 ++++++------
  1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index 88653d1c06a4..b3e3bc59c09b 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -1382,7 +1382,7 @@ static int coresight_fixup_device_conns(struct coresight_device *csdev)
  			continue;
  		conn->child_dev =
  			coresight_find_csdev_by_fwnode(conn->child_fwnode);
-		if (conn->child_dev) {
+		if (conn->child_dev && conn->child_dev->has_conns_grp) {
  			ret = coresight_make_links(csdev, conn,
  						   conn->child_dev);
  			if (ret)
@@ -1594,7 +1594,8 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
  	refcnts = kcalloc(nr_refcnts, sizeof(*refcnts), GFP_KERNEL);
  	if (!refcnts) {
  		ret = -ENOMEM;
-		goto err_free_csdev;
+		kfree(csdev);
+		goto err_out;
  	}
csdev->refcnt = refcnts;
@@ -1619,8 +1620,10 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
  	csdev->dev.fwnode = fwnode_handle_get(dev_fwnode(desc->dev));
  	dev_set_name(&csdev->dev, "%s", desc->name);
+ mutex_lock(&coresight_mutex);
  	ret = device_register(&csdev->dev);
  	if (ret) {
+		mutex_unlock(&coresight_mutex);
  		put_device(&csdev->dev);
  		/*
  		 * All resources are free'd explicitly via
@@ -1634,6 +1637,7 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
  		ret = etm_perf_add_symlink_sink(csdev);
if (ret) {
+			mutex_unlock(&coresight_mutex);
  			device_unregister(&csdev->dev);
  			/*
  			 * As with the above, all resources are free'd
@@ -1645,8 +1649,6 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
  		}
  	}
- mutex_lock(&coresight_mutex);
-
  	ret = coresight_create_conns_sysfs_group(csdev);
  	if (!ret)
  		ret = coresight_fixup_device_conns(csdev);
@@ -1663,8 +1665,6 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
return csdev; -err_free_csdev:
-	kfree(csdev);
  err_out:
  	/* Cleanup the connection information */
  	coresight_release_platform_data(NULL, desc->pdata);

Could we consolidate the unlock sequence to a single point with something like this (untested):


diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index af00dca8d1ac..198ee140c6e6 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -1571,6 +1571,7 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 	int nr_refcnts = 1;
 	atomic_t *refcnts = NULL;
 	struct coresight_device *csdev;
+	bool registered = false;

 	csdev = kzalloc(sizeof(*csdev), GFP_KERNEL);
 	if (!csdev) {
@@ -1591,7 +1592,8 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 	refcnts = kcalloc(nr_refcnts, sizeof(*refcnts), GFP_KERNEL);
 	if (!refcnts) {
 		ret = -ENOMEM;
-		goto err_free_csdev;
+		kfree(csdev);
+		goto err_out;
 	}

 	csdev->refcnt = refcnts;
@@ -1616,6 +1618,13 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 	csdev->dev.fwnode = fwnode_handle_get(dev_fwnode(desc->dev));
 	dev_set_name(&csdev->dev, "%s", desc->name);

+	/*
+	 * Make sure the device registration and the connection fixup
+	 * are synchronised, so that we don't see uninitialised devices
+	 * on the coresight bus while trying to resolve the connections.
+	 */
+	mutex_lock(&coresight_mutex);
+
 	ret = device_register(&csdev->dev);
 	if (ret) {
 		put_device(&csdev->dev);
@@ -1623,7 +1632,7 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 		 * All resources are free'd explicitly via
 		 * coresight_device_release(), triggered from put_device().
 		 */
-		goto err_out;
+		goto out_unlock;
 	}

 	if (csdev->type == CORESIGHT_DEV_TYPE_SINK ||
@@ -1638,11 +1647,11 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 			 * from put_device(), which is in turn called from
 			 * function device_unregister().
 			 */
-			goto err_out;
+			goto out_unlock;
 		}
 	}
-
-	mutex_lock(&coresight_mutex);
+	/* Device is now registered */
+	registered = true;

 	ret = coresight_create_conns_sysfs_group(csdev);
 	if (!ret)
@@ -1652,16 +1661,15 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 	if (!ret && cti_assoc_ops && cti_assoc_ops->add)
 		cti_assoc_ops->add(csdev);

+out_unlock:
 	mutex_unlock(&coresight_mutex);
-	if (ret) {
+	/* Success */
+	if (!ret)
+		return csdev;
+
+	/* Unregister the device if needed */
+	if (registered)
 		coresight_unregister(csdev);
-		return ERR_PTR(ret);
-	}
-
-	return csdev;
-
-err_free_csdev:
-	kfree(csdev);
 err_out:
 	/* Cleanup the connection information */
 	coresight_release_platform_data(NULL, desc->pdata);
--
2.35.1



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