[PATCH 3/5] rbd: don't hold ctl_mutex to get/put device

[Alex Elder <elder@inktank.com>]

When an rbd device is first getting mapped, its device registration
is protected the control mutex.  There is no need to do that though,
because the device has already been assigned an id that's guaranteed
to be unique.

An unmap of an rbd device won't proceed if the device has a non-zero
open count or is already being unmapped.  So there's no need to hold
the control mutex in that case either.

Finally, an rbd device can't be opened if it is being removed, and
it won't go away if there is a non-zero open count.  So here too
there's no need to hold the control mutex while getting or putting a
reference to an rbd device's Linux device structure.

Drop the mutex calls in these cases.

Signed-off-by: Alex Elder <elder@inktank.com>
---
 drivers/block/rbd.c |   17 ++---------------
 1 file changed, 2 insertions(+), 15 deletions(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 380940d..9c81a5c 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -489,10 +489,8 @@ static int rbd_open(struct block_device *bdev,
fmode_t mode)
 	if (removing)
 		return -ENOENT;

-	mutex_lock_nested(&ctl_mutex, SINGLE_DEPTH_NESTING);
 	(void) get_device(&rbd_dev->dev);
 	set_device_ro(bdev, rbd_dev->mapping.read_only);
-	mutex_unlock(&ctl_mutex);

 	return 0;
 }
@@ -507,9 +505,7 @@ static int rbd_release(struct gendisk *disk, fmode_t
mode)
 	spin_unlock_irq(&rbd_dev->lock);
 	rbd_assert(open_count_before > 0);

-	mutex_lock_nested(&ctl_mutex, SINGLE_DEPTH_NESTING);
 	put_device(&rbd_dev->dev);
-	mutex_unlock(&ctl_mutex);

 	return 0;
 }
@@ -4348,8 +4344,6 @@ static int rbd_bus_add_dev(struct rbd_device *rbd_dev)
 	struct device *dev;
 	int ret;

-	mutex_lock_nested(&ctl_mutex, SINGLE_DEPTH_NESTING);
-
 	dev = &rbd_dev->dev;
 	dev->bus = &rbd_bus_type;
 	dev->type = &rbd_device_type;
@@ -4358,8 +4352,6 @@ static int rbd_bus_add_dev(struct rbd_device *rbd_dev)
 	dev_set_name(dev, "%d", rbd_dev->dev_id);
 	ret = device_register(dev);

-	mutex_unlock(&ctl_mutex);
-
 	return ret;
 }

@@ -5165,8 +5157,6 @@ static ssize_t rbd_remove(struct bus_type *bus,
 	if (dev_id != ul)
 		return -EINVAL;

-	mutex_lock_nested(&ctl_mutex, SINGLE_DEPTH_NESTING);
-
 	ret = -ENOENT;
 	spin_lock(&rbd_dev_list_lock);
 	list_for_each(tmp, &rbd_dev_list) {
@@ -5187,7 +5177,7 @@ static ssize_t rbd_remove(struct bus_type *bus,
 	}
 	spin_unlock(&rbd_dev_list_lock);
 	if (ret < 0 || already)
-		goto done;
+		return ret;

 	rbd_bus_del_dev(rbd_dev);
 	ret = rbd_dev_header_watch_sync(rbd_dev, false);
@@ -5195,11 +5185,8 @@ static ssize_t rbd_remove(struct bus_type *bus,
 		rbd_warn(rbd_dev, "failed to cancel watch event (%d)\n", ret);
 	rbd_dev_image_release(rbd_dev);
 	module_put(THIS_MODULE);
-	ret = count;
-done:
-	mutex_unlock(&ctl_mutex);

-	return ret;
+	return count;
 }

 /*
-- 
1.7.9.5