rbd: do not allow remove of mounted-on image

There is no check in rbd_remove() to see if anybody holds open the
image being removed.  That's not cool.

Add a simple open count that goes up and down with opens and closes
(releases) of the device, and don't allow an rbd image to be removed
if the count is non-zero.

Protect the updates of the open count value with ctl_mutex to ensure
the underlying rbd device doesn't get removed while concurrently
being opened.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 842caf4aab47..c7bf9613ad40 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -235,6 +235,7 @@ struct rbd_device {
 
         /* sysfs related */
         struct device           dev;
+        unsigned long           open_count;
 };
 
 static DEFINE_MUTEX(ctl_mutex);   /* Serialize open/close/setup/teardown */
@@ -309,8 +310,11 @@ static int rbd_open(struct block_device *bdev, fmode_t mode)
         if ((mode & FMODE_WRITE) && rbd_dev->mapping.read_only)
                 return -EROFS;
 
+        mutex_lock_nested(&ctl_mutex, SINGLE_DEPTH_NESTING);
         rbd_get_dev(rbd_dev);
         set_device_ro(bdev, rbd_dev->mapping.read_only);
+        rbd_dev->open_count++;
+        mutex_unlock(&ctl_mutex);
 
         return 0;
 }
@@ -319,7 +323,11 @@ static int rbd_release(struct gendisk *disk, fmode_t mode)
 {
         struct rbd_device *rbd_dev = disk->private_data;
 
+        mutex_lock_nested(&ctl_mutex, SINGLE_DEPTH_NESTING);
+        rbd_assert(rbd_dev->open_count > 0);
+        rbd_dev->open_count--;
         rbd_put_dev(rbd_dev);
+        mutex_unlock(&ctl_mutex);
 
         return 0;
 }
@@ -3745,6 +3753,11 @@ static ssize_t rbd_remove(struct bus_type *bus,
                 goto done;
         }
 
+        if (rbd_dev->open_count) {
+                ret = -EBUSY;
+                goto done;
+        }
+
         rbd_remove_all_snaps(rbd_dev);
         rbd_bus_del_dev(rbd_dev);