[PATCH 1/6] rbd: protect read of snapshot sequence number

[Alex Elder <elder@dreamhost.com>]

This is updated whenever a snapshot is added or deleted, and the
snapc pointer is changed with every refresh of the header.

Signed-off-by: Josh Durgin <josh.durgin@dreamhost.com>
Reviewed-by: Alex Elder <elder@dreamhost.com>
---
  drivers/block/rbd.c |    4 +++-
  1 file changed, 3 insertions(+), 1 deletion(-)

Index: b/drivers/block/rbd.c
===================================================================
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -1685,7 +1685,9 @@
  	if (ret < 0)
  		return ret;

-	dev->header.snapc->seq =  new_snapid;
+	down_write(&dev->header_rwsem);
+	dev->header.snapc->seq = new_snapid;
+	up_write(&dev->header_rwsem);

  	return 0;
  bad: