Hi Ma,

Thanks for the update.

On Tue, Mar 18, 2025 at 05:09:45PM +0800, Ma Ke wrote:

Once device_register() failed, we should call put_device() to decrement reference count for cleanup. Or it could cause memory leak. And move callback function before put_device().

As comment of device_register() says, 'NOTE: _Never_ directly free @dev after calling this function, even if it returned an error! Always use put_device() to give up the reference initialized in this function instead.'

Found by code review.

Cc: stable@vger.kernel.org Fixes: baa057e29b58 ("media: v4l2-dev: use pr_foo() for printing messages") Signed-off-by: Ma Ke make24@iscas.ac.cn

---

Changes in v2:

• modified the patch as no callback function before put_device().

---

drivers/media/v4l2-core/v4l2-dev.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c index 5bcaeeba4d09..4a8fdf8115c0 100644 --- a/drivers/media/v4l2-core/v4l2-dev.c +++ b/drivers/media/v4l2-core/v4l2-dev.c @@ -1054,17 +1054,16 @@ int __video_register_device(struct video_device *vdev, vdev->dev.class = &video_class; vdev->dev.devt = MKDEV(VIDEO_MAJOR, vdev->minor); vdev->dev.parent = vdev->dev_parent;

• vdev->dev.release = v4l2_device_release; dev_set_name(&vdev->dev, "%s%d", name_base, vdev->num); mutex_lock(&videodev_lock); ret = device_register(&vdev->dev); if (ret < 0) { mutex_unlock(&videodev_lock); pr_err("%s: device_register failed\n", __func__);

• goto cleanup;
  

• put_device(&vdev->dev);
  

• return ret;
  

  }

• /* Register the release callback that will be called when the last

•   reference to the device goes away. */
  

• vdev->dev.release = v4l2_device_release;

if (nr != -1 && nr != vdev->num && warn_if_nr_in_use) pr_warn("%s: requested %s%d, got %s\n", __func__,

I think this still needs some work. E.g. v4l2_device_get() hasn't been called yet here, but still v4l2_device_release() will call v4l2_device_put().