Do not allow creating snapshots while another snapshot is merging.
Snapshot created in this state would certainly contain invalid data.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 tools/lvcreate.c |    5 +++++
 1 file changed, 5 insertions(+)

Index: LVM2.2.02.39/tools/lvcreate.c
===================================================================
--- LVM2.2.02.39.orig/tools/lvcreate.c	2008-07-30 20:15:56.000000000 +0200
+++ LVM2.2.02.39/tools/lvcreate.c	2008-07-30 20:18:55.000000000 +0200
@@ -657,6 +657,11 @@ static int _lvcreate(struct cmd_context 
 				  "supported yet");
 			return 0;
 		}
+		if (org->merging_snapshot) {
+			log_error("It is not allowed to create snapshot while "
+				  "another snapshot is merging");
+			return 0;
+		}
 		if (org->status & MIRROR_IMAGE ||
 		    org->status & MIRROR_LOG ||
 		    org->status & MIRRORED) {