[Bugfix] Use a separate FlashInfer workspace buffer for trtllm-gen (#25520)

Signed-off-by: yewentao256 <zhyanwentao@126.com>

Author: benchislett

vllm/v1/attention/backends/flashinfer.py

@@ -48,6 +48,16 @@
 
 logger = init_logger(__name__)
 
+trtllm_gen_workspace_buffer = None
+
+
+def _get_trtllm_gen_workspace_buffer():
+    global trtllm_gen_workspace_buffer
+    if trtllm_gen_workspace_buffer is None:
+        trtllm_gen_workspace_buffer = torch.zeros(
+            FLASHINFER_WORKSPACE_BUFFER_SIZE, dtype=torch.uint8, device='cuda')
+    return trtllm_gen_workspace_buffer
+
 
 @triton.jit
 def _trtllm_prefill_attn_kvfp8_dequant(
@@ -862,7 +872,7 @@ def forward(
             else:
                 # prefill_query may be non-contiguous
                 prefill_query = prefill_query.contiguous()
-                workspace_buffer = prefill_wrapper._float_workspace_buffer
+                workspace_buffer = _get_trtllm_gen_workspace_buffer()
                 block_tables_prefill = attn_metadata.block_table_tensor[
                     num_decode_tokens:]
                 seq_lens_prefill = attn_metadata.seq_lens[num_decode_tokens:]
@@ -943,7 +953,7 @@ def forward(
             else:
                 # decode_query may be non-contiguous
                 decode_query = decode_query.contiguous()
-                workspace_buffer = decode_wrapper._float_workspace_buffer
+                workspace_buffer = _get_trtllm_gen_workspace_buffer()
                 block_tables_decode = attn_metadata.\
                     block_table_tensor[:num_decode_tokens]
                 seq_lens_decode = attn_metadata.seq_lens[:num_decode_tokens]