Condition for deadlock occurrence?

Deadlock can arise if four conditions hold simultaneously.

Mutual exclusion:  only one process at a time can use a resource.

Hold and wait:  a process holding at least one resource is waiting to acquire

additional resources held by other processes.

No preemption:  a resource can be released only voluntarily by the process holding it, after that process has completed its task.

Circular wait:  there exists a set {P0, P1, …, P0} of waiting processes such that P0 is waiting for a resource that is held by P1, P1 is waiting for a resource that is held by P2, …, Pn–1 is waiting for a resource that is held by  Pn, and P0 is waiting for a resource that is held by P0.