MDEV-7793 - Race condition between XA COMMIT/ROLLBACK and disconnectbb-mdev7793

XA COMMIT/ROLLBACK of XA transaction owned by different thread may access
freed memory if that thread disconnects at the same time.

Also concurrent XA COMMIT/ROLLBACK of recovered XA transaction were not
serialized properly.

2 files changed, 70 insertions, 0 deletions

diff --git a/mysql-test/r/xa_sync.result b/mysql-test/r/xa_sync.result
new file mode 100644
index 00000000000..769a13d1773
--- /dev/null
+++ b/mysql-test/r/xa_sync.result
@@ -0,0 +1,24 @@
+#
+# MDEV-7793 - Race condition between XA COMMIT/ROLLBACK and disconnect
+#
+# Note that this test is meaningful only with valgrind.
+XA START 'xatest';
+XA END 'xatest';
+XA PREPARE 'xatest';
+SET debug_sync='xa_after_search SIGNAL parked WAIT_FOR go';
+XA COMMIT 'xatest';
+SET debug_sync='now WAIT_FOR parked';
+# Waiting for thread to get deleted
+SET debug_sync='now SIGNAL go';
+ERROR XAE04: XAER_NOTA: Unknown XID
+SET debug_sync='RESET';
+XA START 'xatest';
+XA END 'xatest';
+XA PREPARE 'xatest';
+SET debug_sync='xa_after_search SIGNAL parked WAIT_FOR go';
+XA ROLLBACK 'xatest';
+SET debug_sync='now WAIT_FOR parked';
+# Waiting for thread to get deleted
+SET debug_sync='now SIGNAL go';
+ERROR XAE04: XAER_NOTA: Unknown XID
+SET debug_sync='RESET';
diff --git a/mysql-test/t/xa_sync.test b/mysql-test/t/xa_sync.test
new file mode 100644
index 00000000000..8a995c4a184
--- /dev/null
+++ b/mysql-test/t/xa_sync.test
@@ -0,0 +1,46 @@
+--source include/have_debug_sync.inc
+
+--echo #
+--echo # MDEV-7793 - Race condition between XA COMMIT/ROLLBACK and disconnect
+--echo #
+--echo # Note that this test is meaningful only with valgrind.
+let $op= XA COMMIT 'xatest';
+let $i= 2;
+while ($i)
+{
+  connect con1, localhost, root;
+  connect con2, localhost, root;
+
+  connection con1;
+  XA START 'xatest';
+  XA END 'xatest';
+  XA PREPARE 'xatest';
+
+  connection con2;
+  SET debug_sync='xa_after_search SIGNAL parked WAIT_FOR go';
+  send_eval $op;
+
+  connection default;
+  SET debug_sync='now WAIT_FOR parked';
+  disconnect con1;
+  disable_query_log;
+  echo # Waiting for thread to get deleted;
+  while (`SELECT VARIABLE_VALUE!=2 FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME='max_used_connections'`)
+  {
+    real_sleep 0.1;
+    FLUSH STATUS;
+  }
+  enable_query_log;
+  SET debug_sync='now SIGNAL go';
+
+  connection con2;
+  --error ER_XAER_NOTA
+  reap;
+  disconnect con2;
+
+  connection default;
+  SET debug_sync='RESET';
+
+  let $op= XA ROLLBACK 'xatest';
+  dec $i;
+}