Spack CI: drop the segfault diagnostic step

Removes the 'failure()'-guarded step that ran the element-creation
reproducer under gdb, valgrind and the reference BLAS. It served its
purpose in ruling things out -- the crash is not OpenBLAS kernel
dispatch, not symbol binding, and not reproducible on an Intel host --
but it never ran on an affected AMD EPYC runner, so the fault is still
unexplained and the step has nothing left to add in its present form.

The crash therefore remains: high-degree hexahedral H(curl) element
creation segfaults with a null 'rip' on a varying subset of the matrix
legs, reporting only 'create_element' in the Python traceback. Recover
the instrumentation from 169cf98 if it is wanted again.

The petsc4py marker comment stays: it documents a fix, not a diagnostic,
and the wrong operand order silently skips 174 tests per leg.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: garth-wells

.github/workflows/ci.yml

@@ -227,95 +227,6 @@ jobs:
           python -m pytest -n=auto --durations=50 ${{ !matrix.petsc && '-m "not petsc4py"' || '' }} dolfinx-src/python/test/unit/
           mpiexec -np 3 python -m pytest --durations=50 ${{ !matrix.petsc && '-m "not petsc4py"' || '' }} dolfinx-src/python/test/unit/
 
-      # TEMPORARY DIAGNOSTIC (remove once the crash is understood).
-      # Creating a high-degree hexahedral H(curl) element segfaults with
-      # 'rip' null on a varying subset of the matrix legs. Pinning the
-      # OpenBLAS kernel set ('openblas~dynamic_dispatch') did not help: the
-      # crash reproduced on an AMD EPYC 9V74 runner with a non-dispatching
-      # OpenBLAS whose compiled-in core ('Core: Zen') matched the CPU, and
-      # under OPENBLAS_CORETYPE and LD_BIND_NOW alike. So this now asks the
-      # question that ordering settles: whether the faulting call is a BLAS
-      # call at all. It breaks on the BLAS entry points to print each call
-      # site, and re-runs against the reference BLAS.
-      # Guarded on 'failure()', so it costs nothing on a green leg.
-      - name: Diagnose segfaulting element creation
-        if: failure()
-        continue-on-error: true
-        shell: spack-bash {0}
-        run: |
-          apt-get install -y gdb valgrind libblas3 liblapack3
-          spack env activate ci
-          spack load gcc
-          echo "== CPU =="
-          lscpu | grep -E "Model name|^Flags" | cut -c1-240
-          cat > /tmp/probe_maps.py <<'EOF'
-          import basix.ufl  # noqa: F401
-          libs = {ln.split()[-1] for ln in open("/proc/self/maps") if "blas" in ln.lower()}
-          print(*sorted(libs), sep="\n")
-          EOF
-          echo "== BLAS libraries mapped alongside basix =="
-          python /tmp/probe_maps.py || true
-          echo "== unresolved symbols in the basix extension =="
-          ldd -r $(python -c "import basix._basixcpp as m; print(m.__file__)") 2>&1 \
-            | grep -iE "undefined|not found" | head -20 || echo "none"
-          # libbasix is what calls the BLAS; the extension above only wraps it.
-          echo "== libbasix: BLAS linkage and unresolved symbols =="
-          LIBBASIX=$(spack location -i fenics-basix)/lib/libbasix.so
-          ldd "$LIBBASIX" | grep -iE "blas|lapack" || echo "no BLAS in DT_NEEDED"
-          ldd -r "$LIBBASIX" 2>&1 | grep -iE "undefined|not found" | head -20 || echo "none"
-          cat > /tmp/repro.py <<'EOF'
-          import basix.ufl
-          basix.ufl.element("Nedelec 1st kind H(curl)", "hexahedron", 4)
-          print("element created")
-          EOF
-          echo "== repro, with OpenBLAS core detection =="
-          OPENBLAS_VERBOSE=2 python /tmp/repro.py || true
-          # If the reference BLAS survives what OpenBLAS does not, the fault
-          # is in the BLAS; if both crash, the BLAS is a bystander.
-          echo "== repro, against the reference BLAS =="
-          LD_PRELOAD=/usr/lib/x86_64-linux-gnu/liblapack.so.3:/usr/lib/x86_64-linux-gnu/libblas.so.3 \
-            python /tmp/repro.py || true
-          # Each BLAS entry prints its caller, so the last line before the
-          # crash is the call site -- 'bt' cannot give it once rip is null.
-          cat > /tmp/gdb.cmds <<'EOF'
-          set auto-load safe-path /
-          set disable-randomization off
-          set pagination off
-          set breakpoint pending on
-          break dgemm_
-          break dgesv_
-          break dgetrf_
-          break dgetri_
-          break dsyevd_
-          commands
-          silent
-          frame 1
-          continue
-          end
-          run
-          echo \n== CRASH ==\n
-          bt
-          x/512a $sp
-          info registers
-          EOF
-          echo "== repro under gdb, tracing BLAS call sites =="
-          gdb -q -batch -x /tmp/gdb.cmds --args python /tmp/repro.py 2>&1 | tail -120 || true
-          # A jump to address zero leaves no return address on the stack, so
-          # no unwinder can name the caller -- 'x/512a $sp' came back all
-          # zeros. Valgrind tracks the call chain itself, so it reports the
-          # jump ('Jump to the invalid address ... at 0x0: ??? by 0x...')
-          # together with the frames that led there.
-          echo "== repro under valgrind =="
-          valgrind --error-limit=no --num-callers=30 --trace-children=yes \
-            python /tmp/repro.py 2>&1 | tail -60 || true
-          # Fallback, in case the one-liner above does not reproduce.
-          echo "== affected tests serially under gdb =="
-          gdb -q -batch -ex "set auto-load safe-path /" -ex "set disable-randomization off" \
-            -ex "handle SIGPIPE nostop noprint pass" -ex run \
-            -ex "bt" -ex "x/64a \$rsp" -ex "info registers" \
-            --args python -m pytest -x -p no:cacheprovider -m "not petsc4py" \
-            dolfinx-src/python/test/unit/fem/test_discrete_operators.py || true
-
       # The test tools are environment roots, so '--only dependencies'
       # skips them and they need naming explicitly. Only the final push
       # rebuilds the index, which is the expensive part.