Hey Firedrakers, The attached simple code is failing in parallel but works fine in serial. Specifically, when I run mpirun -n 1 python3 failing_example.py everything is fine. However, using mpirun -n 2 python3 failing_example.py fails with a segfault in PETSc. As far as I can tell (by adding print statements to various parts of the Firedrake src), the segfault is occurring in the set_function method of the _SNESContext class from solving_utils.py, specifically line 130: with self._F.dat.vec_wo as v: I don't know enough about the internals of Firedrake to diagnose the issue beyond that. Any ideas what could be going wrong? I am running a new copy of Firedrake on Ubuntu 18.04. Regards, Chris Eldred -- Chris Eldred https://www.math.univ-paris13.fr/~eldred/ Research Scientist, INRIA/Laboratoire Jean Kuntzmann Postdoctoral Fellow, LAGA, University of Paris 13 PhD, Atmospheric Science, Colorado State University, 2015 DOE Computational Science Graduate Fellow (Alumni) B.S. Applied Computational Physics, Carnegie Mellon University, 2009 chris.eldred@gmail.com