Deadlock can be defined as an unresolved contention for use of a resource. Whenever any mutual exclusion primitive is used, the possibility of deadlock is introduced. This is evident even in uniprocessor system such as OS/2 with the use of semaphores. The possibilities of deadlock are greater in a multiprocessor environment because of the large requirement for mutual exclusion. The method of mutual exclusion for device drivers and the OS/2 SMP kernel is the spinlock. Using spinlocks incorrectly can result in deadlock conditions where an application or device driver will become hung. In the case of a device driver, no more activity will take place on that processor if the device driver enters a deadlock state. Writing device drivers and code for OS/2 for SMP V2.11 requires the programmer to think about the conditions in the code which might cause a deadlock condition, and then use spinlocks to protect those resources.
While it would be impossible to list every cause of deadlock, a few of the most common code examples are given below in pseudo-code that can result in deadlock. These examples are not exhaustive, but represent the majority of situations that will probably be encountered. Being aware of these types of conditions can help you reduce the chances of deadlock within your device driver or applications.