Hi, I have a specific issue that arises with MPICH (I use 3.1.1 built with gcc) + MPI_THREAD_MULTIPLE + per-object critical sections on BG/Q. A deadlock happens in the attached hybrid MPI+OpenMP example code with 2 processes and more than one thread per process. Debugging shows that one process is stuck in MPI_Allreduce while the other is blocked in MPI_Finalize. A similar communication pattern happens in my application, but in this case both processes are stuck in MPI_Allreduce. Note that the problem disappears when removing MPI_Allreduce, or avoiding request cancellation (cancel+wait+test_cancelled). Both Allreduce and cancellation operations can be avoided in this test while ensuring a correct result. But in my application, both operations are necessary. In addition, using a global critical section (default) results in a correct execution. My configure line is as follows: ./configure --prefix=/home/aamer/usr --host=powerpc64-bgq-linux --with-device=pamid --with-file-system=gpfs:BGQ --with-file-system=bg+bglockless --with-atomic-primitives --enable-handle-allocation=tls --enable-refcount=lock-free -disable-predefined-refcount --disable-error-checking --without-timing --without-mpit-pvars --enable-fast=O3,ndebug --enable-thread-cs=per-object I appreciate any advice to solve this issue? Regards, --Halim