The Kernel Debugger is essentially a replacement OS/2 Kernel module that contains a built-in debugger component. The kernel debugger can be used to halt system execution, inspect and alter memory and registers, and display system control blocks. The kernel debugger is described in detail in The OS/2 Debugging Handbook - Volume II, IBM publication number SG24-4641.
The kernel debugger architecture is such that only one thread can be in the debugger at any given time. The kernel debugger in OS/2 Warp Server for SMP serializes its access using a spinlock.
When entered, the debugger informs the user of the state of all the processors, even though the other processors are still executing code. This is accomplished by sending a spin command via an interprocessor interrupt, or IPI, to all the other processors. When a processor receives the spin command, it saves its current state information, acknowledges receiving the command, and then spins. This allows the debugger to switch to a slot which is currently executing on another processor and determine what it is doing.