Re: [PATCH v2] videobuf2: Add missing lock held on vb2_fop_relase

Sylwester Nawrocki
2013-10-19T18:27:08Z

On 10/19/2013 06:07 PM, Ricardo Ribalda wrote:
[...]
> ---
> drivers/media/platform/exynos4-is/fimc-capture.c | 2 +-
> drivers/media/platform/exynos4-is/fimc-lite.c | 2 +-
> drivers/media/usb/em28xx/em28xx-video.c | 2 +-
> drivers/media/v4l2-core/videobuf2-core.c | 18 +++++++++++++++++-
> include/media/videobuf2-core.h | 2 ++
> 5 files changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/media/platform/exynos4-is/fimc-capture.c b/drivers/media/platform/exynos4-is/fimc-capture.c
> index fb27ff7..c38d247c 100644
> --- a/drivers/media/platform/exynos4-is/fimc-capture.c
> +++ b/drivers/media/platform/exynos4-is/fimc-capture.c
> @@ -549,7 +549,7 @@ static int fimc_capture_release(struct file *file)
> vc->streaming = false;
> }
>
> - ret = vb2_fop_release(file);
> + ret = __vb2_fop_release(file, true);
>
> if (close) {
> clear_bit(ST_CAPT_BUSY,&fimc->state);
> diff --git a/drivers/media/platform/exynos4-is/fimc-lite.c b/drivers/media/platform/exynos4-is/fimc-lite.c
> index e5798f7..021d804 100644
> --- a/drivers/media/platform/exynos4-is/fimc-lite.c
> +++ b/drivers/media/platform/exynos4-is/fimc-lite.c
> @@ -546,7 +546,7 @@ static int fimc_lite_release(struct file *file)
> mutex_unlock(&entity->parent->graph_mutex);
> }
>
> - vb2_fop_release(file);
> + __vb2_fop_release(file, true);
> pm_runtime_put(&fimc->pdev->dev);
> clear_bit(ST_FLITE_SUSPENDED,&fimc->state);
>
> diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
> index 9d10334..6a5c147 100644
> --- a/drivers/media/usb/em28xx/em28xx-video.c
> +++ b/drivers/media/usb/em28xx/em28xx-video.c
> @@ -1664,7 +1664,7 @@ static int em28xx_v4l2_close(struct file *filp)
> em28xx_videodbg("users=%d\n", dev->users);
>
> mutex_lock(&dev->lock);
> - vb2_fop_release(filp);
> + __vb2_fop_release(filp, false);

I believe no modifications are needed for this driver.

> if (dev->users == 1) {
> /* the device is already disconnect,
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index 594c75e..ce309a8 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -2619,16 +2619,32 @@ int vb2_fop_mmap(struct file *file, struct vm_area_struct *vma)
> }
> EXPORT_SYMBOL_GPL(vb2_fop_mmap);
>
> -int vb2_fop_release(struct file *file)
> +int __vb2_fop_release(struct file *file, bool lock_is_held)
> {
> struct video_device *vdev = video_devdata(file);
> + struct mutex *lock;
>
> if (file->private_data == vdev->queue->owner) {
> + if (lock_is_held)
> + lock = NULL;
> + else
> + lock = vdev->queue->lock ?
> + vdev->queue->lock : vdev->lock;
> + if (lock)
> + mutex_lock(lock);
> vb2_queue_release(vdev->queue);
> vdev->queue->owner = NULL;
> + if (lock)
> + mutex_unlock(lock);
> }
> return v4l2_fh_release(file);
> }
> +EXPORT_SYMBOL_GPL(__vb2_fop_release);
> +
> +int vb2_fop_release(struct file *file)
> +{
> + return __vb2_fop_release(file, false);
> +}
> EXPORT_SYMBOL_GPL(vb2_fop_release);

It might be better to make it something like:

static int _vb2_fop_release(struct file *file, bool locked)
{
struct video_device *vdev = video_devdata(file);
struct mutex *lock;

if (file->private_data == vdev->queue->owner) {
lock = vdev->queue->lock ?
vdev->queue->lock : vdev->lock;

if (lock && !locked)
mutex_lock(lock);

vb2_queue_release(vdev->queue);
vdev->queue->owner = NULL;
if (lock && !locked)
mutex_unlock(lock);
}
return v4l2_fh_release(file);
}

int vb2_fop_release(struct file *file)
{
return _vb2_fop_release(file, false);
}
EXPORT_SYMBOL_GPL(vb2_fop_release);

/*
* This function should be used instead of vb2_fop_release()
* if the caller already holds the video queue mutex.
*/
int __vb2_fop_release(struct file *file)
{
return _vb2_fop_release(file, true);
}
EXPORT_SYMBOL_GPL(__vb2_fop_release);

since __vb2_fop_release(file, false); is basically useless, it is same
as vb2_fop_release(file);

> ssize_t vb2_fop_write(struct file *file, char __user *buf,
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 6781258..cd1e4d5 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -491,6 +491,8 @@ int vb2_ioctl_expbuf(struct file *file, void *priv,
>
> int vb2_fop_mmap(struct file *file, struct vm_area_struct *vma);
> int vb2_fop_release(struct file *file);
> +/* must be used if the lock is held. */

Let's put any comments at the function body, not here.

> +int __vb2_fop_release(struct file *file, bool lock_is_held);

int __vb2_fop_release(struct file *file);

> ssize_t vb2_fop_write(struct file *file, char __user *buf,
> size_t count, loff_t *ppos);
> ssize_t vb2_fop_read(struct file *file, char __user *buf,

Thanks,
Sylwester