[Fix][AMD] Qwen3.5 MoE: disable global-slot shared-expert fusion under per-rank EP backends (MoRI + dp-attention init crash) (#31793)

python/sglang/srt/models/qwen2_moe.py

@@ -68,6 +68,7 @@ from sglang.srt.layers.moe.utils import (
     RoutingMethodType,
     filter_moe_weight_param_global_expert,
     is_deepep_class_backend,
+    uses_per_rank_fused_shared_slots,
 )
 from sglang.srt.layers.quantization.base_config import QuantizationConfig
 from sglang.srt.layers.radix_attention import RadixAttention
@@ -249,6 +250,20 @@ class Qwen2MoeSparseMoeBlock(nn.Module):
                 self.num_shared_experts > 0
                 and can_fuse_shared_expert(config, quant_config)
             )
+        if (
+            self.enable_shared_expert_fusion
+            and uses_per_rank_fused_shared_slots()
+            and get_parallel().moe_ep_size > 1
+        ):
+            logger.warning_once(
+                "Disabling Qwen shared-expert fusion: it uses a single global "
+                "shared slot with a per-token gate, which is incompatible with "
+                "per-rank EP shared-slot backends (e.g. DeepEP/MoRI) at "
+                "moe_ep_size=%d. Using the separate shared-expert MLP instead.",
+                get_parallel().moe_ep_size,
+            )
+            self.enable_shared_expert_fusion = False
+
         if self.enable_shared_expert_fusion:
             self.num_fused_shared_experts = self.num_shared_experts