[PATCH 3.10 096/129] rbd: protect against concurrent unmaps

[Greg Kroah-Hartman]

3.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alex Elder <elder@xxxxxxxxxxx>

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@xxxxxxxxxxx>
Reviewed-by: Josh Durgin <josh.durgin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -5108,6 +5108,7 @@ static ssize_t rbd_remove(struct bus_typ
 	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_typ
 		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);


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