[BUGFIX] Fix crash in Eagle Speculative Decoding models when exceedin… (#24662)

Signed-off-by: AlonKejzman <alonkeizman@gmail.com>

vllm/v1/worker/gpu_model_runner.py

@@ -2310,7 +2310,20 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
         use_padded_batch_for_eagle = self.speculative_config and \
             self.speculative_config.use_eagle() and \
             not self.speculative_config.disable_padded_drafter_batch
-        if use_padded_batch_for_eagle:
+        effective_drafter_max_model_len = self.max_model_len
+        if effective_drafter_max_model_len is None:
+            effective_drafter_max_model_len = self.model_config.max_model_len
+        if (self.speculative_config
+                and self.speculative_config.draft_model_config is not None
+                and self.speculative_config.draft_model_config.max_model_len
+                is not None):
+            effective_drafter_max_model_len = (
+                self.speculative_config.draft_model_config.max_model_len)
+        input_fits_in_drafter = spec_decode_common_attn_metadata and (
+            spec_decode_common_attn_metadata.seq_lens.max() +
+            self.speculative_config.num_speculative_tokens
+            <= effective_drafter_max_model_len)
+        if use_padded_batch_for_eagle and input_fits_in_drafter:
             # EAGLE speculative decoding can use the GPU sampled tokens
             # as inputs, and does not need to wait for bookkeeping to finish.
             propose_draft_token_ids(sampler_output.sampled_token_ids)
@@ -2328,7 +2341,8 @@ class GPUModelRunner(LoRAModelRunnerMixin, KVConnectorModelRunnerMixin):
                                        logits, hidden_states,
                                        num_scheduled_tokens)
 
-        if self.speculative_config and not use_padded_batch_for_eagle:
+        if (self.speculative_config and not use_padded_batch_for_eagle
+                and input_fits_in_drafter):
             # ngram and other speculative decoding methods use the sampled
             # tokens on the CPU, so they are run after bookkeeping.
             propose_draft_token_ids(valid_sampled_token_ids)