How to lock all tables except some specific table?
Do not use LOCK TABLES with InnoDB.  For this situation consider the following...


Leave read_only = OFF
Provide a readonly login for your application when it goes to the Slave in addition to a readwrite login for when it talks to the Master.


The app user would have grants something like:

GRANT SELECT         ON app_db.*   TO app_user@slave
GRANT ALL PRIVILEGES ON sessions.* TO app_user@slave   -- and cache.*
GRANT ALL PRIVILEGES ON app_db.*   TO app_user@master