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

Nicolas Dufresne
2025-06-04T23:11:21Z

Le mercredi 04 juin 2025 à 21:33 +0000, Sakari Ailus a écrit :
> Hi Nicolas, Hans,
>
> Thanks for the update.

thanks for the review, these things are precious.

>
> On Wed, Jun 04, 2025 at 04:09:37PM -0400, Nicolas Dufresne wrote:
> > 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.
> > + */
>
> Fits on a single line.

Ack.

>
> > +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));
>
> Newline here?

I prefer that too.

>
> > + 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
>
> I have no objection to this but it would have been great to have the Media
> device lifetime set in first and MC device and devnode merged. But maybe
> it's too late for that. Well, at least this won't change error handling...

Since this specific patch is not required to fix the MTK VCODEC issue, I can
delay this a little. Is that comment related to an existing patch ?

>
> > +
> >   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
>
> This deserves at least a comment what this may be used for: generally once
> object is unbound, it's not related to a request anymore (nor a Media
> device). This field also adds a new Media device lifetime issue: nothing

We could make it explicit by clearing the mdev pointer ?

> guarantees the mdev is not disappearing at a wrong time albeit this is
> very, very likely not user-triggerable without physically removing
> hardware.

I'm not too familiar with the subject, if the MC knows it has open request
FD(s), why would it allow userspace from unloading its module ?

>
> >   * @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;
> >