rbd: protect against concurrent unmaps

commit 82a442d239695a242c4d584464c9606322cd02aa upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index afdbd558485d9a97f710d350f61ffb1584b32ab1..8326b39b0576974a1a4f12e646ce208ef1313790 100644 (file)
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -5108,6 +5108,7 @@ 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);
@@ -5135,11 +5136,12 @@ 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);