Fix Whisper crash caused by invalid max_num_batched_tokens config (#17853)

Signed-off-by: inkcherry <mingzhi.liu@intel.com>

Author: inkcherry

vllm/config.py

@@ -2050,6 +2050,13 @@ def __post_init__(self) -> None:
                     _MULTIMODAL_MODEL_MAX_NUM_BATCHED_TOKENS,
                 )
 
+            # When using default settings,
+            # Ensure max_num_batched_tokens does not exceed model limit.
+            # Some models (e.g., Whisper) have embeddings tied to max length.
+            self.max_num_batched_tokens = min(
+                self.max_num_seqs * self.max_model_len,
+                self.max_num_batched_tokens)
+
         self.max_num_encoder_input_tokens = self.max_num_batched_tokens
         self.encoder_cache_size = self.max_num_batched_tokens
 
@@ -2090,6 +2097,13 @@ def _verify_args(self) -> None:
                 "be greater than or equal to max_num_seqs "
                 f"({self.max_num_seqs}).")
 
+        if self.max_num_batched_tokens > self.max_num_seqs * self.max_model_len:
+            logger.warning(
+                "max_num_batched_tokens (%d) exceeds max_num_seqs"
+                "* max_model_len (%d). This may lead to unexpected behavior.",
+                self.max_num_batched_tokens,
+                self.max_num_seqs * self.max_model_len)
+
         if self.num_lookahead_slots < 0:
             raise ValueError(
                 "num_lookahead_slots "