[PATCH 2/5] rbd: protect against concurrent unmaps

[Alex Elder <elder@inktank.com>]

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>
---
 drivers/block/rbd.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 716ef1f..380940d 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -5153,6 +5153,7 @@ 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);
@@ -5180,11 +5181,12 @@ 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);
-- 
1.7.9.5