MDEV-19826 10.4 seems to crash with "pool-of-threads" (#1370)

MariaDB 10.4 was crashing when thread-handling was set to
pool-of-threads and wsrep was enabled.

There were two apparent reasons for the crash:
- Connection handling in threadpool_common.cc was missing calls to
  control wsrep client state.
- Thread specific storage which contains thread variables (THR_KEY_mysys)
  was not handled appropriately by wsrep patch when pool-of-threads
  was configured.

This patch addresses the above issues in the following way:
- Wsrep client state open/close was moved in thd_prepare_connection() and
  end_connection() to have common handling for one-thread-per-connection
  and pool-of-threads.
- Thread local storage handling in wsrep patch was reworked by introducing
  set of wsrep_xxx_threadvars() calls which replace calls to
  THD store_globals()/reset_globals() and deal with thread handling
  specifics internally.

Wsrep-lib was updated to version which relaxes internal concurrency
related sanity checks.

Rollback code from wsrep_rollback_process() was extracted to separate calls
for better readability.

Post rollback thread was removed as it was completely unused.

1 files changed, 5 insertions, 2 deletions

diff --git a/sql/wsrep_sst.cc b/sql/wsrep_sst.cc
index e2878211d7e..62b30c0d67d 100644
--- a/sql/wsrep_sst.cc
+++ b/sql/wsrep_sst.cc
@@ -27,6 +27,8 @@
 #include "wsrep_priv.h"
 #include "wsrep_utils.h"
 #include "wsrep_xid.h"
+#include "wsrep_thd.h"
+
 #include <cstdio>
 #include <cstdlib>
 
@@ -237,7 +239,7 @@ void wsrep_sst_received (THD*                thd,
       wsrep thread pool. Restore original thd context before returning.
     */
     if (thd) {
-      thd->store_globals();
+      wsrep_store_threadvars(thd);
     }
     else {
       my_pthread_setspecific_ptr(THR_THD, NULL);
@@ -509,7 +511,8 @@ err:
     thd->system_thread= SYSTEM_THREAD_GENERIC;
     thd->real_id= pthread_self();
 
-    thd->store_globals();
+    wsrep_assign_from_threadvars(thd);
+    wsrep_store_threadvars(thd);
 
     /* */
     thd->variables.wsrep_on    = 0;