branches/5.1: lock_is_table_exclusive(): Acquire kernel_mutex before

accessing table->locks and release kernel_mutex before returning from
the function.  This fixes a portential race condition in the
"commit every 10,000 rows" in ALTER TABLE, CREATE INDEX, DROP INDEX,
and OPTIMIZE TABLE. (Bug #42152)

rb://80 approved by Heikki Tuuri

lock/lock0lock.c

@@ -681,7 +681,10 @@ lock_is_table_exclusive(
 	lock_t*	lock;
 	ibool	ok	= FALSE;
 
-	ut_ad(table && trx);
+	ut_ad(table);
+	ut_ad(trx);
+
+	lock_mutex_enter_kernel();
 
 	for (lock = UT_LIST_GET_FIRST(table->locks);
 	     lock;
@@ -689,7 +692,7 @@ lock_is_table_exclusive(
 		if (lock->trx != trx) {
 			/* A lock on the table is held
 			by some other transaction. */
-			return(FALSE);
+			goto not_ok;
 		}
 
 		if (!(lock_get_type(lock) & LOCK_TABLE)) {
@@ -706,11 +709,16 @@ lock_is_table_exclusive(
 			auto_increment lock. */
 			break;
 		default:
+not_ok:
 			/* Other table locks than LOCK_IX are not allowed. */
-			return(FALSE);
+			ok = FALSE;
+			goto func_exit;
 		}
 	}
 
+func_exit:
+	lock_mutex_exit_kernel();
+
 	return(ok);
 }
 
@@ -3664,6 +3672,7 @@ lock_table_has_to_wait_in_queue(
 	dict_table_t*	table;
 	lock_t*		lock;
 
+	ut_ad(mutex_own(&kernel_mutex));
 	ut_ad(lock_get_wait(wait_lock));
 
 	table = wait_lock->un_member.tab_lock.table;