MySQL got signal 11 error and slave is down
The reason for this ? Please note the following diagram of the InnoDB Architecture



From this diagram, you can see an insert buffer in the InnoDB Buffer Pool and a connection to the insert buffer in ibdata1. This thread is known as the Master Thread. In its current design, InnoDB can only have one Master Thread per MySQL Instance.

Apparently, given the messages above, mysqld is trying to start and another mysqld process is already running. You need to go to the OS do the following:


Locate the mysqld_safe process and kill it
Locate the mysqld process and kill it
Run service mysql start
If mysqld complains about the PID file already existing, delete the PID file and try to start mysql again.