MDEV-22370 safe_mutex: Trying to lock uninitialized mutex at /data/src/10.4-bug/sql/rpl_parallel.cc, line 470 upon shutdown during FTWRL

Problem:- When we issue FTWRL with shutdown in parallel, there is race between
FTWRL and shutdown. Shutdown might destroy the mutex (pool->LOCK_rpl_thread_pool)
before FTWRL can lock it. So we can get crash on FTWRL thread

Solution:- mysql_mutex_destroy(pool->LOCK_rpl_thread_pool) should wait for
FTWRL thread to complete its work , and then destroy.
So slave_prepare_for_shutdown will just deactivate the pool, and mutex is destroyed
later in end_slave()

1 files changed, 15 insertions, 0 deletions

diff --git a/sql/rpl_parallel.cc b/sql/rpl_parallel.cc
index 88e036d4481..7c0e96bc8ed 100644
--- a/sql/rpl_parallel.cc
+++ b/sql/rpl_parallel.cc
@@ -467,6 +467,7 @@ pool_mark_busy(rpl_parallel_thread_pool *pool, THD *thd)
     So we protect the infrequent operations of FLUSH TABLES WITH READ LOCK and
     pool size changes with this condition wait.
   */
+  DBUG_EXECUTE_IF("mark_busy_mdev_22370",my_sleep(1000000););
   mysql_mutex_lock(&pool->LOCK_rpl_thread_pool);
   if (thd)
   {
@@ -2011,9 +2012,23 @@ rpl_parallel_thread_pool::init(uint32 size)
 void
 rpl_parallel_thread_pool::destroy()
 {
+  deactivate();
+  destroy_cond_mutex();
+}
+
+void
+rpl_parallel_thread_pool::deactivate()
+{
   if (!inited)
     return;
   rpl_parallel_change_thread_count(this, 0, 1);
+}
+
+void
+rpl_parallel_thread_pool::destroy_cond_mutex()
+{
+  if (!inited)
+    return;
   mysql_mutex_destroy(&LOCK_rpl_thread_pool);
   mysql_cond_destroy(&COND_rpl_thread_pool);
   inited= false;