MLK-11508-1: Revert "[media] v4l2-core: remove the old .ioctl BKL replacement"

This reverts commit 5cf6f7f327.

drivers/media/v4l2-core/v4l2-dev.c

@@ -360,6 +360,34 @@ static long v4l2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			ret = vdev->fops->unlocked_ioctl(filp, cmd, arg);
 		if (lock)
 			mutex_unlock(lock);
+	} else if (vdev->fops->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.
+		 *
+		 * All drivers implement struct v4l2_device, so we use the
+		 * lock defined there to serialize the ioctls.
+		 *
+		 * However, 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.
+		 */
+		struct mutex *m = &vdev->v4l2_dev->ioctl_lock;
+
+		if (cmd != VIDIOC_DQBUF && mutex_lock_interruptible(m))
+			return -ERESTARTSYS;
+		if (video_is_registered(vdev))
+			ret = vdev->fops->ioctl(filp, cmd, arg);
+		if (cmd != VIDIOC_DQBUF)
+			mutex_unlock(m);
 	} else
 		ret = -ENOTTY;
 

drivers/media/v4l2-core/v4l2-device.c

@@ -37,6 +37,7 @@ int v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev)
 
 	INIT_LIST_HEAD(&v4l2_dev->subdevs);
 	spin_lock_init(&v4l2_dev->lock);
+	mutex_init(&v4l2_dev->ioctl_lock);
 	v4l2_prio_init(&v4l2_dev->prio);
 	kref_init(&v4l2_dev->ref);
 	get_device(dev);

include/media/v4l2-dev.h

@@ -153,6 +153,7 @@ struct v4l2_file_operations {
 	ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
 	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
 	unsigned int (*poll) (struct file *, struct poll_table_struct *);
+	long (*ioctl) (struct file *, unsigned int, unsigned long);
 	long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
 #ifdef CONFIG_COMPAT
 	long (*compat_ioctl32) (struct file *, unsigned int, unsigned long);

include/media/v4l2-device.h

@@ -69,6 +69,8 @@ struct v4l2_device {
 			unsigned int notification, void *arg);
 	struct v4l2_ctrl_handler *ctrl_handler;
 	struct v4l2_prio_state prio;
+	/* BKL replacement mutex. Temporary solution only. */
+	struct mutex ioctl_lock;
 	struct kref ref;
 	void (*release)(struct v4l2_device *v4l2_dev);
 };