Detect blocking process [on hold]

How can I detect in Linux blocked processes in the following process chains (process A is blocked)

• A -> B


• A -> B -> C

I would like to know which are the blocking processes (B and C), in order to take some actions. Is there a command or a set of commands for that?

To be more clear, in QNX pidin command gives you STATE and Blocked columns. If A is blocked to B (waits an reply from B) the STATE will be REPLY and in the BLOCKED column will be the process ID (B process'ID). I am wondering if there is such a command in linux as well.