rbd: protect against concurrent unmaps

Make sure two concurrent unmap operations on the same rbd device
won't collide, by only proceeding with the removal and cleanup of a
device if is not already underway.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 9eead4879c90..305c740778c6 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -5137,6 +5137,7 @@ static ssize_t rbd_remove(struct bus_type *bus,
         struct list_head *tmp;
         int dev_id;
         unsigned long ul;
+        bool already = false;
         int ret;
 
         ret = strict_strtoul(buf, 10, &ul);
@@ -5164,11 +5165,12 @@ static ssize_t rbd_remove(struct bus_type *bus,
                 if (rbd_dev->open_count)
                         ret = -EBUSY;
                 else
-                        set_bit(RBD_DEV_FLAG_REMOVING, &rbd_dev->flags);
+                        already = test_and_set_bit(RBD_DEV_FLAG_REMOVING,
+                                                        &rbd_dev->flags);
                 spin_unlock_irq(&rbd_dev->lock);
         }
         spin_unlock(&rbd_dev_list_lock);
-        if (ret < 0)
+        if (ret < 0 || already)
                 goto done;
 
         rbd_bus_del_dev(rbd_dev);