From: leo@yuriev.ru <leo@yuriev.ru>
Date: Fri, 17 Oct 2014 22:35:41 +0000 (+0000)
Subject: ITS#7970 LMDB: Critical Heisenbug
X-Git-Tag: LMDB_0.9.15~32
X-Git-Url: https://git.sur5r.net/?p=openldap;a=commitdiff_plain;h=8230b1b63003f5e4910948687c0ceba0bed1d624

ITS#7970 LMDB: Critical Heisenbug

Inconsistent reading & SIGSEGV due to the race condition.
---

diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 89d4a2a257..27dbb9b1ae 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -2539,7 +2539,10 @@ mdb_txn_renew0(MDB_txn *txn)
 					return rc;
 				}
 			}
-			txn->mt_txnid = r->mr_txnid = ti->mti_txnid;
+			do /* LY: Retry on a race, ITS#7970. */
+				r->mr_txnid = ti->mti_txnid;
+			while(r->mr_txnid != ti->mti_txnid);
+			txn->mt_txnid = r->mr_txnid;
 			txn->mt_u.reader = r;
 			meta = env->me_metas[txn->mt_txnid & 1];
 		}