1 files changed, 51 insertions, 18 deletions

diff --git a/drivers/media/video/v4l2-dev.c b/drivers/media/video/v4l2-dev.c
index 03f7f46..359e232 100644
--- a/drivers/media/video/v4l2-dev.c
+++ b/drivers/media/video/v4l2-dev.c
@@ -186,12 +186,12 @@ static ssize_t v4l2_read(struct file *filp, char __user *buf,
 		size_t sz, loff_t *off)
 {
 	struct video_device *vdev = video_devdata(filp);
-	int ret = -EIO;
+	int ret = -ENODEV;
 
 	if (!vdev->fops->read)
 		return -EINVAL;
-	if (vdev->lock)
-		mutex_lock(vdev->lock);
+	if (vdev->lock && mutex_lock_interruptible(vdev->lock))
+		return -ERESTARTSYS;
 	if (video_is_registered(vdev))
 		ret = vdev->fops->read(filp, buf, sz, off);
 	if (vdev->lock)
@@ -203,12 +203,12 @@ static ssize_t v4l2_write(struct file *filp, const char __user *buf,
 		size_t sz, loff_t *off)
 {
 	struct video_device *vdev = video_devdata(filp);
-	int ret = -EIO;
+	int ret = -ENODEV;
 
 	if (!vdev->fops->write)
 		return -EINVAL;
-	if (vdev->lock)
-		mutex_lock(vdev->lock);
+	if (vdev->lock && mutex_lock_interruptible(vdev->lock))
+		return -ERESTARTSYS;
 	if (video_is_registered(vdev))
 		ret = vdev->fops->write(filp, buf, sz, off);
 	if (vdev->lock)
@@ -219,10 +219,10 @@ static ssize_t v4l2_write(struct file *filp, const char __user *buf,
 static unsigned int v4l2_poll(struct file *filp, struct poll_table_struct *poll)
 {
 	struct video_device *vdev = video_devdata(filp);
-	int ret = DEFAULT_POLLMASK;
+	int ret = POLLERR | POLLHUP;
 
 	if (!vdev->fops->poll)
-		return ret;
+		return DEFAULT_POLLMASK;
 	if (vdev->lock)
 		mutex_lock(vdev->lock);
 	if (video_is_registered(vdev))
@@ -238,20 +238,45 @@ static long v4l2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	int ret = -ENODEV;
 
 	if (vdev->fops->unlocked_ioctl) {
-		if (vdev->lock)
-			mutex_lock(vdev->lock);
+		if (vdev->lock && mutex_lock_interruptible(vdev->lock))
+			return -ERESTARTSYS;
 		if (video_is_registered(vdev))
 			ret = vdev->fops->unlocked_ioctl(filp, cmd, arg);
 		if (vdev->lock)
 			mutex_unlock(vdev->lock);
 	} else if (vdev->fops->ioctl) {
-		/* TODO: convert all drivers to unlocked_ioctl */
+		/* This code path is a replacement for the BKL. It is a major
+		 * hack but it will have to do for those drivers that are not
+		 * yet converted to use unlocked_ioctl.
+		 *
+		 * There are two options: if the driver implements struct
+		 * v4l2_device, then the lock defined there is used to
+		 * serialize the ioctls. Otherwise the v4l2 core lock defined
+		 * below is used. This lock is really bad since it serializes
+		 * completely independent devices.
+		 *
+		 * Both variants suffer from the same problem: if the driver
+		 * sleeps, then it blocks all ioctls since the lock is still
+		 * held. This is very common for VIDIOC_DQBUF since that
+		 * normally waits for a frame to arrive. As a result any other
+		 * ioctl calls will proceed very, very slowly since each call
+		 * will have to wait for the VIDIOC_QBUF to finish. Things that
+		 * should take 0.01s may now take 10-20 seconds.
+		 *
+		 * The workaround is to *not* take the lock for VIDIOC_DQBUF.
+		 * This actually works OK for videobuf-based drivers, since
+		 * videobuf will take its own internal lock.
+		 */
 		static DEFINE_MUTEX(v4l2_ioctl_mutex);
+		struct mutex *m = vdev->v4l2_dev ?
+			&vdev->v4l2_dev->ioctl_lock : &v4l2_ioctl_mutex;
 
-		mutex_lock(&v4l2_ioctl_mutex);
+		if (cmd != VIDIOC_DQBUF && mutex_lock_interruptible(m))
+			return -ERESTARTSYS;
 		if (video_is_registered(vdev))
 			ret = vdev->fops->ioctl(filp, cmd, arg);
-		mutex_unlock(&v4l2_ioctl_mutex);
+		if (cmd != VIDIOC_DQBUF)
+			mutex_unlock(m);
 	} else
 		ret = -ENOTTY;
 
@@ -265,8 +290,8 @@ static int v4l2_mmap(struct file *filp, struct vm_area_struct *vm)
 
 	if (!vdev->fops->mmap)
 		return ret;
-	if (vdev->lock)
-		mutex_lock(vdev->lock);
+	if (vdev->lock && mutex_lock_interruptible(vdev->lock))
+		return -ERESTARTSYS;
 	if (video_is_registered(vdev))
 		ret = vdev->fops->mmap(filp, vm);
 	if (vdev->lock)
@@ -284,7 +309,7 @@ static int v4l2_open(struct inode *inode, struct file *filp)
 	mutex_lock(&videodev_lock);
 	vdev = video_devdata(filp);
 	/* return ENODEV if the video device has already been removed. */
-	if (vdev == NULL) {
+	if (vdev == NULL || !video_is_registered(vdev)) {
 		mutex_unlock(&videodev_lock);
 		return -ENODEV;
 	}
@@ -292,8 +317,10 @@ static int v4l2_open(struct inode *inode, struct file *filp)
 	video_get(vdev);
 	mutex_unlock(&videodev_lock);
 	if (vdev->fops->open) {
-		if (vdev->lock)
-			mutex_lock(vdev->lock);
+		if (vdev->lock && mutex_lock_interruptible(vdev->lock)) {
+			ret = -ERESTARTSYS;
+			goto err;
+		}
 		if (video_is_registered(vdev))
 			ret = vdev->fops->open(filp);
 		else
@@ -302,6 +329,7 @@ static int v4l2_open(struct inode *inode, struct file *filp)
 			mutex_unlock(vdev->lock);
 	}
 
+err:
 	/* decrease the refcount in case of an error */
 	if (ret)
 		video_put(vdev);
@@ -596,7 +624,12 @@ void video_unregister_device(struct video_device *vdev)
 	if (!vdev || !video_is_registered(vdev))
 		return;
 
+	mutex_lock(&videodev_lock);
+	/* This must be in a critical section to prevent a race with v4l2_open.
+	 * Once this bit has been cleared video_get may never be called again.
+	 */
 	clear_bit(V4L2_FL_REGISTERED, &vdev->flags);
+	mutex_unlock(&videodev_lock);
 	device_unregister(&vdev->dev);
 }
 EXPORT_SYMBOL(video_unregister_device);