Use !critsec to find out, which thread is waiting for a critical section

If you need to find out which thread is owning a critical section a blocked thread is waiting for you can first get the stack args by

kb

Then you need to get the critical section address from the stack. This is an argument passed to ntdll!RtlEnterCriticalSection API as first parameter.

By typing

!critsec 'address'

You'll get information about the section like: LockCount, RecursionCount, OwningThread, EntryCount, ContentionCount and the Locked state.

CritSec +81347c at 0081347c
LockCount 8
RecursionCount 1
OwningThread c6c
EntryCount 8
ContentionCount 8
*** Locked