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>

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index bfdd8f5fa340b4faf519132aa9afc4d510c4771d..719a5237402dcbfee4d26af01876a8609fe05a89 100644 (file)
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -5157,6 +5157,7 @@ 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);
@@ -5184,11 +5185,12 @@ 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);