Stop (coreml, models) hanging at the 180 minute CI cap

.ci/scripts/test_backend.sh

@@ -157,7 +157,15 @@ EXIT_CODE=0
 # a step that size, taking the whole job down before pytest can report. The
 # reason for each failure is in its exception message and traceback, which are
 # unaffected.
-PYTEST_ARGS=(-c /dev/null -n auto --show-capture=no)
+# faulthandler_timeout is pytest's built-in stack dumper, so this adds no
+# dependency and fails nothing: after 15 minutes in one test case it prints
+# every thread's traceback and the case keeps running. A case that wedges
+# otherwise leaves no trace at all - the job is cancelled at the job cap, the
+# JSON report below is never written, and the artifact upload fails - which is
+# how (coreml, models) spent a month at the 180 minute cap with no one able to
+# say which model was stuck or where. Raise the value if a legitimate case ever
+# runs this long.
+PYTEST_ARGS=(-c /dev/null -o faulthandler_timeout=900 -n auto --show-capture=no)
 if [[ ${#PYTEST_RETRY_ARGS[@]} -gt 0 ]]; then
     PYTEST_ARGS+=("${PYTEST_RETRY_ARGS[@]}")
 fi

backends/test/suite/models/test_torchvision.py

@@ -40,11 +40,20 @@ def _test_cv_model(
     # Test a CV model that follows the standard conventions.
     inputs = (torch.randn(1, 3, 224, 224, dtype=dtype),)
 
+    # The declared minimum is 2, not 1. Until #23326 the exported program's
+    # range constraints were recomputed from the ShapeEnv after every pass, and
+    # the ShapeEnv raises a backed symbol's declared minimum of 0 or 1 to 2, so
+    # a declared min=1 never reached a backend: these models have always been
+    # lowered over height/width in [32, 256]. #23326 made ExecuTorch keep the
+    # declared range instead, which handed backends a lower bound of 16 for the
+    # first time and let a 16x16 input - degenerate for a network with a total
+    # stride of 32 - into backend shape reasoning. Declaring 2 states the bound
+    # that was always in force.
     dynamic_shapes = (
         (
             {
-                2: Dim("height", min=1, max=16) * 16,
-                3: Dim("width", min=1, max=16) * 16,
+                2: Dim("height", min=2, max=16) * 16,
+                3: Dim("width", min=2, max=16) * 16,
             },
         )
         if use_dynamic_shapes