Merge from 5.0-pe-stage into main.

1 files changed, 16 insertions, 0 deletions

diff --git a/sql/sql_lex.h b/sql/sql_lex.h
index 9f020f4adc5..3e762581e04 100644
--- a/sql/sql_lex.h
+++ b/sql/sql_lex.h
@@ -1176,6 +1176,22 @@ typedef struct st_lex : public Query_tables_list
 
   bool escape_used;
 
+  /*
+    Special case for SELECT .. FOR UPDATE and LOCK TABLES .. WRITE.
+
+    Protect from a impending GRL as otherwise the thread might deadlock
+    if it starts waiting for the GRL in mysql_lock_tables.
+
+    The protection is needed because there is a race between setting
+    the global read lock and waiting for all open tables to be closed.
+    The problem is a circular wait where a thread holding "old" open
+    tables will wait for the global read lock to be released while the
+    thread holding the global read lock will wait for all "old" open
+    tables to be closed -- the flush part of flush tables with read
+    lock.
+  */
+  bool protect_against_global_read_lock;
+
   st_lex();
 
   virtual ~st_lex()