ITS#7635 fix read txn potential data race

diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 40b46e8b9ca4241bd6e4ee5c6725a942ce17c762..84405e89634f0b31d319bd01c7246b46a8a3d5c1 100644 (file)
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -1743,6 +1743,7 @@ mdb_txn_renew0(MDB_txn *txn)
        unsigned int i;
        uint16_t x;
        int rc, new_notls = 0;
+       pgno_t lastpg2;
 
        /* Setup db info */
        txn->mt_numdbs = env->me_numdbs;
@@ -1811,6 +1812,17 @@ mdb_txn_renew0(MDB_txn *txn)
 
        /* Copy the DB info and flags */
        memcpy(txn->mt_dbs, env->me_metas[txn->mt_toggle]->mm_dbs, 2 * sizeof(MDB_db));
+       /* In a read txn, there is a data race here. Make sure our
+        * last_pg/next_pg are up to date.
+        */
+       lastpg2 = env->me_metas[txn->mt_toggle]->mm_last_pg+1;
+       if (lastpg2 != txn->mt_next_pgno) {
+               txn->mt_next_pgno = lastpg2;
+               /* When this situation occurs, the txnid will certainly also
+                * be out of date. But as noted before, we don't care about having
+                * up to date read txn IDs.
+                */
+       }
        for (i=2; i<txn->mt_numdbs; i++) {
                x = env->me_dbflags[i];
                txn->mt_dbs[i].md_flags = x & PERSISTENT_FLAGS;