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>

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 78f0752ac781ab4e943a8c067fdbf8ba9ae5a959..17cea6c0c28add0eb2c2df80e886ed91e9afa892 100644 (file)
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -255,6 +255,7 @@ struct rbd_device {
 
        /* sysfs related */
        struct device           dev;
+       unsigned long           open_count;
 };
 
 static DEFINE_MUTEX(ctl_mutex);          /* Serialize open/close/setup/teardown */
@@ -356,8 +357,11 @@ 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;
 }
@@ -366,7 +370,11 @@ 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;
 }
@@ -3764,6 +3772,11 @@ 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);