Monitor: check spare group is non-NULL before adding to domain list

... otherwise we crash.

Reported-by: "Labun, Marcin" <Marcin.Labun@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 3 insertions, 1 deletions

diff --git a/Monitor.c b/Monitor.c
index b907cf2d..e0c86917 100644
--- a/Monitor.c
+++ b/Monitor.c
@@ -732,7 +732,9 @@ static int move_spare(struct state *from, struct state *to,
 				continue;
 
 			pol = devnum_policy(from->devid[d]);
-			pol_add(&pol, pol_domain, from->spare_group, NULL);
+			if (from->spare_group)
+				pol_add(&pol, pol_domain,
+					from->spare_group, NULL);
 			if (domain_test(domlist, pol, to->metadata->ss->name))
 			    dev = from->devid[d];
 			dev_policy_free(pol);