Bug#32528 Global read lock with a low priority write lock causes a server crash

FLUSH TABLES WITH READ LOCK fails to properly detect write locked
tables when running under low priority updates.

The problem is that when trying to aspire a global read lock, the
reload_acl_and_cache() function fails to properly check if the thread
has a low priority write lock, which later my cause a server crash or
deadlock.

The solution is to simple check if the thread has any type of the
possible exclusive write locks.


mysql-test/r/flush.result:
  Add test case result for Bug#32528
mysql-test/t/flush.test:
  Add test case for Bug#32528
sql/sql_parse.cc:
  Although it should not matter under LOCK TABLES, use TL_WRITE_ALLOW_WRITE
  to emphasize that it should fail in case of any write lock.

1 files changed, 17 insertions, 0 deletions

diff --git a/mysql-test/r/flush.result b/mysql-test/r/flush.result
index 7eb7fd16edb..ce64e09c1d3 100644
--- a/mysql-test/r/flush.result
+++ b/mysql-test/r/flush.result
@@ -55,3 +55,20 @@ flush tables with read lock;
 insert into t2 values(1);
 unlock tables;
 drop table t1, t2;
+drop table if exists t1, t2;
+set session low_priority_updates=1;
+create table t1 (a int);
+create table t2 (b int);
+lock tables t1 write;
+flush tables with read lock;
+ERROR HY000: Can't execute the given command because you have active locked tables or an active transaction
+unlock tables;
+lock tables t1 read, t2 write;
+flush tables with read lock;
+ERROR HY000: Can't execute the given command because you have active locked tables or an active transaction
+unlock tables;
+lock tables t1 read;
+flush tables with read lock;
+unlock tables;
+drop table t1, t2;
+set session low_priority_updates=default;