media: v4l2-core: push taking ioctl mutex down to ioctl handler

The ioctl serialization mutex (vdev->lock or q->lock for vb2 queues)
was taken at the highest level in v4l2-dev.c. This prevents more
fine-grained locking since at that level we cannot examine the ioctl
arguments, we can only do that after video_usercopy is called.

So push the locking down to __video_do_ioctl() and subdev_do_ioctl_lock().

This also allows us to make a few functions in v4l2-ioctl.c static and
video_usercopy() is no longer exported.

The locking scheme is not changed by this patch, just pushed down.

Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

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

@@ -360,14 +360,8 @@ static long v4l2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	int ret = -ENODEV;
 
 	if (vdev->fops->unlocked_ioctl) {
-		struct mutex *lock = v4l2_ioctl_get_lock(vdev, cmd);
-
-		if (lock && mutex_lock_interruptible(lock))
-			return -ERESTARTSYS;
 		if (video_is_registered(vdev))
 			ret = vdev->fops->unlocked_ioctl(filp, cmd, arg);
-		if (lock)
-			mutex_unlock(lock);
 	} else
 		ret = -ENOTTY;
 

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

@@ -2655,14 +2655,15 @@ static struct v4l2_ioctl_info v4l2_ioctls[] = {
 };
 #define V4L2_IOCTLS ARRAY_SIZE(v4l2_ioctls)
 
-bool v4l2_is_known_ioctl(unsigned int cmd)
+static bool v4l2_is_known_ioctl(unsigned int cmd)
 {
 	if (_IOC_NR(cmd) >= V4L2_IOCTLS)
 		return false;
 	return v4l2_ioctls[_IOC_NR(cmd)].ioctl == cmd;
 }
 
-struct mutex *v4l2_ioctl_get_lock(struct video_device *vdev, unsigned cmd)
+static struct mutex *v4l2_ioctl_get_lock(struct video_device *vdev,
+					 unsigned int cmd)
 {
 	if (_IOC_NR(cmd) >= V4L2_IOCTLS)
 		return vdev->lock;
@@ -2713,6 +2714,7 @@ static long __video_do_ioctl(struct file *file,
 		unsigned int cmd, void *arg)
 {
 	struct video_device *vfd = video_devdata(file);
+	struct mutex *lock; /* ioctl serialization mutex */
 	const struct v4l2_ioctl_ops *ops = vfd->ioctl_ops;
 	bool write_only = false;
 	struct v4l2_ioctl_info default_info;
@@ -2731,6 +2733,16 @@ static long __video_do_ioctl(struct file *file,
 	if (test_bit(V4L2_FL_USES_V4L2_FH, &vfd->flags))
 		vfh = file->private_data;
 
+	lock = v4l2_ioctl_get_lock(vfd, cmd);
+
+	if (lock && mutex_lock_interruptible(lock))
+		return -ERESTARTSYS;
+
+	if (!video_is_registered(vfd)) {
+		ret = -ENODEV;
+		goto unlock;
+	}
+
 	if (v4l2_is_known_ioctl(cmd)) {
 		info = &v4l2_ioctls[_IOC_NR(cmd)];
 
@@ -2780,6 +2792,9 @@ done:
 		}
 	}
 
+unlock:
+	if (lock)
+		mutex_unlock(lock);
 	return ret;
 }
 
@@ -2969,7 +2984,6 @@ out:
 	kvfree(mbuf);
 	return err;
 }
-EXPORT_SYMBOL(video_usercopy);
 
 long video_ioctl2(struct file *file,
 	       unsigned int cmd, unsigned long arg)

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

@@ -502,10 +502,25 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
 	return 0;
 }
 
+static long subdev_do_ioctl_lock(struct file *file, unsigned int cmd, void *arg)
+{
+	struct video_device *vdev = video_devdata(file);
+	struct mutex *lock = vdev->lock;
+	long ret = -ENODEV;
+
+	if (lock && mutex_lock_interruptible(lock))
+		return -ERESTARTSYS;
+	if (video_is_registered(vdev))
+		ret = subdev_do_ioctl(file, cmd, arg);
+	if (lock)
+		mutex_unlock(lock);
+	return ret;
+}
+
 static long subdev_ioctl(struct file *file, unsigned int cmd,
 	unsigned long arg)
 {
-	return video_usercopy(file, cmd, arg, subdev_do_ioctl);
+	return video_usercopy(file, cmd, arg, subdev_do_ioctl_lock);
 }
 
 #ifdef CONFIG_COMPAT

include/media/v4l2-dev.h

@@ -435,15 +435,6 @@ void video_device_release(struct video_device *vdev);
  */
 void video_device_release_empty(struct video_device *vdev);
 
-/**
- * v4l2_is_known_ioctl - Checks if a given cmd is a known V4L ioctl
- *
- * @cmd: ioctl command
- *
- * returns true if cmd is a known V4L2 ioctl
- */
-bool v4l2_is_known_ioctl(unsigned int cmd);
-
 /**
  * v4l2_disable_ioctl- mark that a given command isn't implemented.
  *	shouldn't use core locking

include/media/v4l2-ioctl.h

@@ -658,18 +658,6 @@ void v4l_printk_ioctl(const char *prefix, unsigned int cmd);
 
 struct video_device;
 
-
-/**
- * v4l2_ioctl_get_lock - get the mutex (if any) that it is need to lock for
- *	a given command.
- *
- * @vdev: Pointer to struct &video_device.
- * @cmd: Ioctl name.
- *
- * .. note:: Internal use only. Should not be used outside V4L2 core.
- */
-struct mutex *v4l2_ioctl_get_lock(struct video_device *vdev, unsigned int cmd);
-
 /* names for fancy debug output */
 extern const char *v4l2_field_names[];
 extern const char *v4l2_type_names[];