[PATCH v3 3/5] media: mc: add debugfs node to keep track of requests

Nicolas Dufresne
2025-06-04T20:22:53Z

From: Hans Verkuil <hverkuil@xs4all.nl>

Keep track of the number of requests and request objects of a media
device. Helps to verify that all request-related memory is freed.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
---
drivers/media/mc/mc-device.c | 30 ++++++++++++++++++++++++++++++
drivers/media/mc/mc-devnode.c | 5 +++++
drivers/media/mc/mc-request.c | 6 ++++++
include/media/media-device.h | 9 +++++++++
include/media/media-devnode.h | 4 ++++
include/media/media-request.h | 2 ++
6 files changed, 56 insertions(+)

diff --git a/drivers/media/mc/mc-device.c b/drivers/media/mc/mc-device.c
index c0dd4ae5722725f1744bc6fd6282d5c765438059..5a458160200afb540d8014fed42d8bf2dab9c8c3 100644
--- a/drivers/media/mc/mc-device.c
+++ b/drivers/media/mc/mc-device.c
@@ -679,6 +679,23 @@ void media_device_unregister_entity(struct media_entity *entity)
}
EXPORT_SYMBOL_GPL(media_device_unregister_entity);

+#ifdef CONFIG_DEBUG_FS
+/*
+ * Log the state of media requests.
+ * Very useful for debugging.
+ */
+static int media_device_requests(struct seq_file *file, void *priv)
+{
+ struct media_device *dev = dev_get_drvdata(file->private);
+
+ seq_printf(file, "number of requests: %d\n",
+ atomic_read(&dev->num_requests));
+ seq_printf(file, "number of request objects: %d\n",
+ atomic_read(&dev->num_request_objects));
+ return 0;
+}
+#endif
+
void media_device_init(struct media_device *mdev)
{
INIT_LIST_HEAD(&mdev->entities);
@@ -697,6 +714,9 @@ void media_device_init(struct media_device *mdev)
media_set_bus_info(mdev->bus_info, sizeof(mdev->bus_info),
mdev->dev);

+ atomic_set(&mdev->num_requests, 0);
+ atomic_set(&mdev->num_request_objects, 0);
+
dev_dbg(mdev->dev, "Media device initialized\n");
}
EXPORT_SYMBOL_GPL(media_device_init);
@@ -748,6 +768,15 @@ int __must_check __media_device_register(struct media_device *mdev,

dev_dbg(mdev->dev, "Media device registered\n");

+#ifdef CONFIG_DEBUG_FS
+ if (!media_debugfs_root)
+ media_debugfs_root = debugfs_create_dir("media", NULL);
+ mdev->media_dir = debugfs_create_dir(dev_name(&devnode->dev),
+ media_debugfs_root);
+ debugfs_create_devm_seqfile(&devnode->dev, "requests",
+ mdev->media_dir, media_device_requests);
+#endif
+
return 0;
}
EXPORT_SYMBOL_GPL(__media_device_register);
@@ -824,6 +853,7 @@ void media_device_unregister(struct media_device *mdev)

dev_dbg(mdev->dev, "Media device unregistered\n");

+ debugfs_remove_recursive(mdev->media_dir);
device_remove_file(&mdev->devnode->dev, &dev_attr_model);
media_devnode_unregister(mdev->devnode);
/* devnode free is handled in media_devnode_*() */
diff --git a/drivers/media/mc/mc-devnode.c b/drivers/media/mc/mc-devnode.c
index 56444edaf13651874331e7c04e86b0a585067d38..d0a8bcc11dd6350fdbc04add70f62de2c5f01178 100644
--- a/drivers/media/mc/mc-devnode.c
+++ b/drivers/media/mc/mc-devnode.c
@@ -45,6 +45,9 @@ static dev_t media_dev_t;
static DEFINE_MUTEX(media_devnode_lock);
static DECLARE_BITMAP(media_devnode_nums, MEDIA_NUM_DEVICES);

+/* debugfs */
+struct dentry *media_debugfs_root;
+
/* Called when the last user of the media device exits. */
static void media_devnode_release(struct device *cd)
{
@@ -236,6 +239,7 @@ int __must_check media_devnode_register(struct media_device *mdev,
if (devnode->parent)
devnode->dev.parent = devnode->parent;
dev_set_name(&devnode->dev, "media%d", devnode->minor);
+ dev_set_drvdata(&devnode->dev, mdev);
device_initialize(&devnode->dev);

/* Part 2: Initialize the character device */
@@ -313,6 +317,7 @@ static int __init media_devnode_init(void)

static void __exit media_devnode_exit(void)
{
+ debugfs_remove_recursive(media_debugfs_root);
bus_unregister(&media_bus_type);
unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);
}
diff --git a/drivers/media/mc/mc-request.c b/drivers/media/mc/mc-request.c
index 398d0806d1d274eb8c454fc5c37b77476abe1e74..829e35a5d56d41c52cc583cdea1c959bcb4fce60 100644
--- a/drivers/media/mc/mc-request.c
+++ b/drivers/media/mc/mc-request.c
@@ -75,6 +75,7 @@ static void media_request_release(struct kref *kref)
mdev->ops->req_free(req);
else
kfree(req);
+ atomic_dec(&mdev->num_requests);
}

void media_request_put(struct media_request *req)
@@ -326,6 +327,7 @@ int media_request_alloc(struct media_device *mdev, int *alloc_fd)

snprintf(req->debug_str, sizeof(req->debug_str), "%u:%d",
atomic_inc_return(&mdev->request_id), fd);
+ atomic_inc(&mdev->num_requests);
dev_dbg(mdev->dev, "request: allocated %s\n", req->debug_str);

fd_install(fd, filp);
@@ -349,10 +351,12 @@ static void media_request_object_release(struct kref *kref)
struct media_request_object *obj =
container_of(kref, struct media_request_object, kref);
struct media_request *req = obj->req;
+ struct media_device *mdev = obj->mdev;

if (WARN_ON(req))
media_request_object_unbind(obj);
obj->ops->release(obj);
+ atomic_dec(&mdev->num_request_objects);
}

struct media_request_object *
@@ -417,6 +421,7 @@ int media_request_object_bind(struct media_request *req,
obj->req = req;
obj->ops = ops;
obj->priv = priv;
+ obj->mdev = req->mdev;

if (is_buffer)
list_add_tail(&obj->list, &req->objects);
@@ -424,6 +429,7 @@ int media_request_object_bind(struct media_request *req,
list_add(&obj->list, &req->objects);
req->num_incomplete_objects++;
ret = 0;
+ atomic_inc(&obj->mdev->num_request_objects);

unlock:
spin_unlock_irqrestore(&req->lock, flags);
diff --git a/include/media/media-device.h b/include/media/media-device.h
index 53d2a16a70b0d9d6e5cc28fe1fc5d5ef384410d5..749c327e3c582c3c583e0394468321ccd6160da5 100644
--- a/include/media/media-device.h
+++ b/include/media/media-device.h
@@ -11,6 +11,7 @@
#ifndef _MEDIA_DEVICE_H
#define _MEDIA_DEVICE_H

+#include <linux/atomic.h>
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/pci.h>
@@ -106,6 +107,9 @@ struct media_device_ops {
* @ops: Operation handler callbacks
* @req_queue_mutex: Serialise the MEDIA_REQUEST_IOC_QUEUE ioctl w.r.t.
* other operations that stop or start streaming.
+ * @num_requests: number of associated requests
+ * @num_request_objects: number of associated request objects
+ * @media_dir: DebugFS media directory
* @request_id: Used to generate unique request IDs
*
* This structure represents an abstract high-level media device. It allows easy
@@ -179,6 +183,11 @@ struct media_device {
const struct media_device_ops *ops;

struct mutex req_queue_mutex;
+ atomic_t num_requests;
+ atomic_t num_request_objects;
+
+ /* debugfs */
+ struct dentry *media_dir;
atomic_t request_id;
};

diff --git a/include/media/media-devnode.h b/include/media/media-devnode.h
index d27c1c646c2805171be3997d72210dd4d1a38e32..dbcabeffcb572ae707f5fe1f51ff719d451c6784 100644
--- a/include/media/media-devnode.h
+++ b/include/media/media-devnode.h
@@ -20,9 +20,13 @@
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/cdev.h>
+#include <linux/debugfs.h>

struct media_device;

+/* debugfs top-level media directory */
+extern struct dentry *media_debugfs_root;
+
/*
* Flag to mark the media_devnode struct as registered. Drivers must not touch
* this flag directly, it will be set and cleared by media_devnode_register and
diff --git a/include/media/media-request.h b/include/media/media-request.h
index 7f9af68ef19ac6de0184bbb0c0827dc59777c6dc..610ccfe8d7b20ec38e166383433f9ee208248640 100644
--- a/include/media/media-request.h
+++ b/include/media/media-request.h
@@ -292,6 +292,7 @@ struct media_request_object_ops {
* struct media_request_object - An opaque object that belongs to a media
* request
*
+ * @mdev: Media device this object belongs to
* @ops: object's operations
* @priv: object's priv pointer
* @req: the request this object belongs to (can be NULL)
@@ -303,6 +304,7 @@ struct media_request_object_ops {
* another struct that contains the actual data for this request object.
*/
struct media_request_object {
+ struct media_device *mdev;
const struct media_request_object_ops *ops;
void *priv;
struct media_request *req;

--
2.49.0