From 0e6a64712a74d33ac43e1bb9ecb5ff652117f19d Mon Sep 17 00:00:00 2001
From: Xinyi Song <86638975+RolaoDenthu@users.noreply.github.com>
Date: Wed, 4 Mar 2026 19:48:15 -0800
Subject: [PATCH] [bugfix] Fix PPMissingLayer AttributeError when Using PP
 (#19804)

---
 python/sglang/srt/layers/utils/common.py | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/python/sglang/srt/layers/utils/common.py b/python/sglang/srt/layers/utils/common.py
index b982b247e..63e32409b 100644
--- a/python/sglang/srt/layers/utils/common.py
+++ b/python/sglang/srt/layers/utils/common.py
@@ -59,12 +59,28 @@ class PPMissingLayer(torch.nn.Identity):
     # https://github.com/vllm-project/vllm/blob/18ed3132d2bfe1df9a74729457b69243955221e8/vllm/model_executor/models/utils.py#L468C1-L486C1
     """
     A placeholder layer for missing layers in a pipeline parallel model.
+
+    Attribute access on this placeholder returns 'self' so that common
+    patterns like ``isinstance(layer.mlp, SomeMoE)`` safely evaluate to
+    ``False`` instead of raising ``AttributeError``.
     """
 
     def __init__(self, *args, **kwargs):
         super().__init__()
         self.return_tuple = kwargs.get("return_tuple", False)
 
+    def __getattr__(self, name: str):
+        try:
+            return super().__getattr__(name)
+        except (AttributeError, KeyError):
+            return self
+
+    def __setattr__(self, name: str, value):
+        if name == "return_tuple" or name.startswith("_"):
+            super().__setattr__(name, value)
+        else:
+            pass
+
     def forward(self, *args, **kwargs):
         """
         Return the first arg from args or the first value from kwargs.