Update on "Make CI error on inductor fallback when decomp is available"

Fixes #99446 

Remove the warning, as that annoyed end-users who don't know what to do about it.

Instead, try to hold the line by preventing any decomp from being added without making
the corresponding change to inductor's fallbacks.

Note: we probably still need to better document how to update inductor's decomps,
for now it's pretty much "go ask the inductor team for advice"

cc soumith voznesenskym penguinwu anijain2305 EikanWang jgong5 Guobing-Chen XiaobingSuper zhuhaozhe blzheng Xia-Weiwen wenzhe-nrv jiayisunx peterbell10 desertfire

[ghstack-poisoned]

torch/_dynamo/allowed_functions.py

@@ -146,6 +146,7 @@ def _is_allowed_module_prefix(obj):
             "torch._C.inductor.",
             "torch.fx.",
             "torch.distributed.fsdp.",
+            "torch.distributed.nn.functional",
         )
         allowed_modules_dot = tuple([x + "." for x in allowed_modules])
         module = inspect.getmodule(obj)

torch/_inductor/lowering.py

@@ -1,7 +1,6 @@
 import functools
 import itertools
 import logging
-import sys
 from collections.abc import Iterable
 from typing import List, Optional, Tuple
 
@@ -1090,16 +1089,14 @@ def make_fallback(kernel, layout_constraint=None, warn=True):
     if get_decompositions([kernel]) and warn and IS_CI:
         # Note: 'warn' is holdover from when this was a warning, but for ops that previously
         # set warn=False we do not want a CI error.
-        log.error(
-            "make_fallback(%s): a decomposition exists, we should switch to it."
+        # Ignore the 'suppress errors' configs in CI, as this particular warning happens on startup anyway and is not
+        # likely to be triggered preferentially on one CI config over another.
+        raise AssertionError(
+            f"make_fallback({kernel}): a decomposition exists, we should switch to it."
             " To fix this error, either add a decomposition to core_aten_decompositions (preferred)"
             " or inductor_decompositions, and delete the corresponding `make_fallback` line."
             " Get help from the inductor team if unsure, don't pick arbitrarily to unblock yourself.",
-            kernel,
         )
-        # Make sure the process exits and CI flags an error, raising
-        # an exception could allow a graph-break and silently pass CI in some configs
-        sys.exit(1)
 
     add_needs_realized_inputs(kernel)
     if layout_constraint is not None: