MDEV-20247 Replication hangs with "preparing" and never starts

- The commit ab6dd774 wrongly sets the
condition inside innobase_srv_conc_enter_innodb().  Problem is that
InnoDB makes the thread to sleep indefinitely if it is a replication
slave thread.

Thanks to Sujatha Sivakumar for contributing the replication test case.

mysql-test/suite/rpl/r/rpl_sync_with_innodb_thd_conc.result

+include/master-slave.inc
+[connection master]
+SET @old_innodb_thread_concurrency := @@innodb_thread_concurrency;
+SET @old_innodb_thread_sleep_delay := @@innodb_thread_sleep_delay;
+SET GLOBAL innodb_thread_concurrency = 100;
+CREATE TABLE t(f INT) ENGINE=INNODB;
+INSERT INTO t VALUES (10);
+include/diff_tables.inc [master:t, slave:t]
+"===== Clean up======="
+DROP TABLE t;
+SET GLOBAL innodb_thread_concurrency = @old_innodb_thread_concurrency;
+SET GLOBAL innodb_thread_sleep_delay = @old_innodb_thread_sleep_delay;
+include/rpl_end.inc

mysql-test/suite/rpl/t/rpl_sync_with_innodb_thd_conc.test

+# ==== Purpose ====
+#
+# Test verifies that replication shouldn't hang when number of active threads
+# on the slave server are less than the allowed innodb_thread_concurrency value.
+#
+# ==== Implementation ====
+#
+# Steps:
+#    0 - Have master slave replication setup with engine being Innodb.
+#    1 - Configure innodb_thread_concurrency = 100.
+#    2 - Do some DML on master and sync the slave with master.
+#    3 - Ensure replication doesn't hang.
+#
+# ==== References ====
+#
+# MDEV-20247: Replication hangs with "preparing" and never starts
+#
+
+--source include/master-slave.inc
+--source include/have_innodb.inc
+
+--connection slave
+SET @old_innodb_thread_concurrency := @@innodb_thread_concurrency;
+SET @old_innodb_thread_sleep_delay := @@innodb_thread_sleep_delay;
+SET GLOBAL innodb_thread_concurrency = 100;
+
+--connection master
+CREATE TABLE t(f INT) ENGINE=INNODB;
+INSERT INTO t VALUES (10);
+--sync_slave_with_master
+
+--let $diff_tables=master:t, slave:t
+--source include/diff_tables.inc
+
+--echo "===== Clean up======="
+--connection master
+DROP TABLE t;
+--sync_slave_with_master
+SET GLOBAL innodb_thread_concurrency = @old_innodb_thread_concurrency;
+SET GLOBAL innodb_thread_sleep_delay = @old_innodb_thread_sleep_delay;
+--source include/rpl_end.inc

storage/innobase/handler/ha_innodb.cc

@@ -1686,9 +1686,9 @@ innobase_srv_conc_enter_innodb(
 			   && thd_is_replication_slave_thread(trx->mysql_thd)) {
 			const ulonglong end = my_interval_timer()
 				+ ulonglong(srv_replication_delay) * 1000000;
-			while (srv_conc_get_active_threads()
-			       >= srv_thread_concurrency
-			       || my_interval_timer() >= end) {
+			while ((srv_conc_get_active_threads()
+			        >= srv_thread_concurrency)
+			       && my_interval_timer() < end) {
 				os_thread_sleep(2000 /* 2 ms */);
 			}
 		} else {

storage/xtradb/handler/ha_innodb.cc

@@ -1949,9 +1949,9 @@ innobase_srv_conc_enter_innodb(
 			   && thd_is_replication_slave_thread(trx->mysql_thd)) {
 			const ulonglong end = my_interval_timer()
 				+ ulonglong(srv_replication_delay) * 1000000;
-			while (srv_conc_get_active_threads()
-			       >= srv_thread_concurrency
-			       || my_interval_timer() >= end) {
+			while ((srv_conc_get_active_threads()
+			        >= srv_thread_concurrency)
+			       && my_interval_timer() < end) {
 				os_thread_sleep(2000 /* 2 ms */);
 			}
 		} else {