locking-functions: Update reference manual (#16854)

functions-and-operators/locking-functions.md

@@ -5,7 +5,7 @@ summary: Learn about user-level locking functions in TiDB.
 
 # Locking Functions
 
-TiDB supports most of the user-level [locking functions](https://dev.mysql.com/doc/refman/5.7/en/locking-functions.html) available in MySQL 5.7.
+TiDB supports most of the user-level [locking functions](https://dev.mysql.com/doc/refman/8.0/en/locking-functions.html) available in MySQL 8.0.
 
 ## Supported functions
 
@@ -20,6 +20,6 @@ TiDB supports most of the user-level [locking functions](https://dev.mysql.com/d
 ## MySQL compatibility
 
 * The minimum timeout permitted by TiDB is 1 second, and the maximum timeout is 1 hour (3600 seconds). This differs from MySQL, where both 0 second and unlimited timeouts (`timeout=-1`) are permitted. TiDB will automatically convert out-of-range values to the nearest permitted value and convert `timeout=-1` to 3600 seconds.
-* TiDB does not automatically detect deadlocks caused by user-level locks. Deadlocked sessions will timeout after a maximum of 1 hour, but can also be manually resolved by using `KILL` on one of the affected sessions. You can also prevent deadlocks by always acquiring user-level locks in the same order.
+* TiDB does not automatically detect deadlocks caused by user-level locks. Deadlocked sessions will timeout after a maximum of 1 hour, but can also be manually resolved by using [`KILL`](/sql-statements/sql-statement-kill.md) on one of the affected sessions. You can also prevent deadlocks by always acquiring user-level locks in the same order.
 * Locks take effect on all TiDB servers in the cluster. This differs from MySQL Cluster and Group Replication where locks are local to a single server.
 * `IS_USED_LOCK()` returns `1` if it is called from another session and is unable to return the ID of the process that is holding the lock.