V4L/DVB: v4l2: add core serialization lock
Drivers can optionally set a pointer to a mutex in struct video_device.
The core will use that to lock before calling open, read, write, unlocked_ioctl,
poll, mmap or release.
Updated the documentation as well and ensure that v4l2-event knows about the
lock: it will unlock it before doing a blocking wait on an event and relock it
afterwards.
Ensure that the 'video_is_registered' check is done when the lock is held:
a typical disconnect will take the lock as well before unregistering the
device nodes, so to prevent race conditions the video_is_registered check
should also be done with the lock held.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/video/v4l2-event.c b/drivers/media/video/v4l2-event.c
index de74ce0..69fd343 100644
--- a/drivers/media/video/v4l2-event.c
+++ b/drivers/media/video/v4l2-event.c
@@ -134,15 +134,22 @@
if (nonblocking)
return __v4l2_event_dequeue(fh, event);
+ /* Release the vdev lock while waiting */
+ if (fh->vdev->lock)
+ mutex_unlock(fh->vdev->lock);
+
do {
ret = wait_event_interruptible(events->wait,
events->navailable != 0);
if (ret < 0)
- return ret;
+ break;
ret = __v4l2_event_dequeue(fh, event);
} while (ret == -ENOENT);
+ if (fh->vdev->lock)
+ mutex_lock(fh->vdev->lock);
+
return ret;
}
EXPORT_SYMBOL_GPL(v4l2_event_dequeue);