rgw: clear old zone short ids on period update

the short ids of old, removed zones were being kept in the period to
guard against hash collisions with new zones

but for a hash collision to cause a wrong object to sync, that object
would have to be uploaded simultaneously to two different zones that had
the same short id

to avoid this, we just have to prevent the period from containing two
colliding zones at the same time - we don't have to remember old zone
short ids forever

Fixes: http://tracker.ceph.com/issues/15618
Signed-off-by: Casey Bodley <cbodley@redhat.com>
(cherry picked from commit 9c45633c836c966ab1f75ea2b1ad3fa0a4886600)

diff --git a/src/rgw/rgw_rados.cc b/src/rgw/rgw_rados.cc
index d6284c777807fa2ae0a5c5de7689520a37e8cef0..dc227815d8108d3c7d892dde0c36ef1d8a9f2110 100644 (file)
--- a/src/rgw/rgw_rados.cc
+++ b/src/rgw/rgw_rados.cc
@@ -1176,6 +1176,10 @@ int RGWPeriod::update()
     return ret;
   }
 
+  // clear zone short ids of removed zones. period_map.update() will add the
+  // remaining zones back
+  period_map.short_zone_ids.clear();
+
   for (auto& iter : zonegroups) {
     RGWZoneGroup zg(string(), iter);
     ret = zg.init(cct, store);