MDEV-7864: Slave SQL: stopping on non-last RBR event with annotations results in SEGV (signal 11)

The slave SQL thread was clearing serial_rgi->thd before deleting
serial_rgi, which could cause access to NULL THD.

The clearing was introduced in commit
2e100cc5a493b6a0f6f907e0483a734c7fee2087 and is just plain wrong. So revert
that part (single line) of that commit.

Thanks to Daniel Black for bug analysis and test case.

1 files changed, 29 insertions, 0 deletions

diff --git a/mysql-test/extra/rpl_tests/rpl_row_annotate.test b/mysql-test/extra/rpl_tests/rpl_row_annotate.test
index f3d8006ce01..0614ca97f1d 100644
--- a/mysql-test/extra/rpl_tests/rpl_row_annotate.test
+++ b/mysql-test/extra/rpl_tests/rpl_row_annotate.test
@@ -101,6 +101,35 @@ if (!$annotate)
 {
   --echo # No Annotate_rows events should appear below
 }
+
+
+
+--echo ########################################################################
+--echo # Ensure that a replication failure doesn't segfault - MDEV-7864
+--echo ########################################################################
+DELETE FROM t3 WHERE a=2;
+connection master;
+INSERT INTO t5 (a) SELECT a.a*10000+b.a*1000+c.a*100+d.a*10 FROM t5 a, t5 b, t5 c, t5 d;
+INSERT INTO t3 (a) SELECT a FROM t5 WHERE a > 10;
+DELETE t3 FROM t3 INNER JOIN t5 ON t3.a=t5.a;
+connection slave;
+--echo ---- Wait until slave stops with an error ----
+# Wait until the slave tries to run the query, fails with key not
+# found error, and stops the SQL thread.
+let $slave_sql_errno= 1032; # Can't find record
+source include/wait_for_slave_sql_error.inc;
+--let $err= query_get_value("SHOW SLAVE STATUS", Last_SQL_Error, 1)
+--replace_regex /end_log_pos [0-9]+/end_log_pos END_LOG_POS/
+--disable_query_log
+--eval SELECT "$err" as 'Last_SQL_Error (expected "Delete_rows_v1 event on table test1.t3; Can\'t find record in \'t3\'" error)'
+--enable_query_log
+call mtr.add_suppression("Slave: Can't find record in 't3' Error_code: 1032");
+
+SET GLOBAL sql_slave_skip_counter=1;
+START SLAVE;
+connection master;
+sync_slave_with_master;
+
 --echo ########################################################################
 FLUSH LOGS;