Once held, any other process seeking to obtain the mutex will wait until the process holding it has finished modifying the list and released the mutex.
Processes cooperate in the sharing of system resources, such as the disks and memory. The top and bottom halves of the kernel also work together in implementing certain system operations, such as I/O. Typically, the top half will start an I/O operation, and then relinquish the processor; then the requesting process will sleep, awaiting notification from the bottom half that the I/O request has completed.