[Bug] Fix FlashInfer allreduce fusion workspace uninitialized error (#37461)

Signed-off-by: root <root@prenyx0169.a51.clusters.nvidia.com>
Signed-off-by: wzhao18 <wzhao18.sz@gmail.com>
Signed-off-by: <>
Co-authored-by: root <root@prenyx0169.a51.clusters.nvidia.com>
Co-authored-by: root <root@prenyx0042.a51.clusters.nvidia.com>

vllm/compilation/passes/fusion/allreduce_rms_fusion.py

@@ -86,8 +86,6 @@ if flashinfer_comm is not None:
         destroy_fi_ar_workspace,
         get_fi_ar_quant_workspace,
         get_fi_ar_workspace,
-        initialize_fi_ar_quant_workspace,
-        initialize_fi_ar_workspace,
     )
 
     ar_fusion_patterns = flashinfer_comm.AllReduceFusionPattern
@@ -133,15 +131,23 @@ if flashinfer_comm is not None:
 
         # Select workspace based on pattern: quant patterns use the
         # trtllm quant workspace, non-quant patterns use the primary workspace.
-        if pattern_code in (
+        is_quant_pattern = pattern_code in (
             ar_fusion_patterns.kARResidualRMSNormFP8Quant,
             ar_fusion_patterns.kARResidualRMSNormFP4Quant,
-        ):
-            workspace = get_fi_ar_quant_workspace()
-        else:
-            workspace = get_fi_ar_workspace()
+        )
+        get_workspace_fn = (
+            get_fi_ar_quant_workspace if is_quant_pattern else get_fi_ar_workspace
+        )
+        workspace = get_workspace_fn(
+            world_size=world_size,
+            rank=get_tensor_model_parallel_rank(),
+            max_token_num=max_token_num,
+            hidden_dim=hidden_size,
+            dtype=allreduce_in.dtype,
+            group=get_tp_group().device_group,
+        )
         assert workspace is not None, (
-            "Flashinfer workspace must be initialized when using flashinfer"
+            "Flashinfer allreduce workspace must be initialized when using flashinfer"
         )
         assert flashinfer_comm is not None
         if norm_out is None:
@@ -753,12 +759,7 @@ class AllReduceFusionPass(VllmPatternMatcherPass):
             scope="global",
         )
 
-        for workspace_init_fn in [
-            initialize_fi_ar_workspace,
-            initialize_fi_ar_quant_workspace,
-        ]:
-            try:
-                workspace_init_fn(
+        workspace_kwargs = dict(
             world_size=self.tp_size,
             rank=rank,
             max_token_num=self.max_token_num,
@@ -766,23 +767,22 @@ class AllReduceFusionPass(VllmPatternMatcherPass):
             dtype=self.model_dtype,
             group=self.group,
         )
-            except Exception as e:
-                if "multicast" in str(e).lower():
-                    logger.warning(
-                        "AllReduce fusion pass is disabled: flashinfer workspace "
-                        "creation failed: %s. This is expected on GPUs without "
-                        "NVSwitch (e.g., NVLink bridge-only or PCIe topologies). "
-                        "Falling back to non-fused allreduce.",
-                        str(e),
-                    )
-                else:
-                    logger.warning(
-                        "Failed to initialize FlashInfer All Reduce workspace: %s. "
-                        "AllReduce fusion pass will be disabled.",
-                        e,
+        if get_fi_ar_workspace(**workspace_kwargs) is None:
+            logger.warning_once(
+                "Failed to initialize Flashinfer allreduce workspace. "
+                "Flashinfer allreduce-norm fusion will be disabled."
             )
             return
 
+        self.supports_quant_fusion = (
+            get_fi_ar_quant_workspace(**workspace_kwargs) is not None
+        )
+        if not self.supports_quant_fusion:
+            logger.warning_once(
+                "Failed to initialize Flashinfer allreduce workspace. "
+                "Flashinfer allreduce-norm-quant fusion will be disabled."
+            )
+
         self.allreduce_params = FlashInferFusedAllReduceParams(
             world_size=self.tp_size,
             max_token_num=self.max_token_num,
@@ -793,9 +793,8 @@ class AllReduceFusionPass(VllmPatternMatcherPass):
 
     @enable_fake_mode
     def register_patterns(self) -> None:
-        supports_quantization = get_fi_ar_quant_workspace() is not None
         for epsilon in [1e-5, 1e-6]:
-            if supports_quantization:
+            if self.supports_quant_fusion:
                 AllReduceFusedRMSNormStaticQuantFP8Pattern(
                     epsilon,
                     self.model_dtype,

vllm/distributed/device_communicators/flashinfer_all_reduce.py

@@ -29,50 +29,27 @@ try:
 except ImportError:
     pass
 
-# Global workspace for standalone allreduce and non-quant ar+rms fusion
+# Workspace for standalone allreduce and non-quant ar+rms fusion
 _fi_ar_workspace = None
 # Extra workspace for quant fusion patterns (only supported by trtllm backend)
-# Only created if primary workspace is not already trtllm
 _fi_ar_quant_workspace = None
 
 
-def get_fi_ar_workspace():
-    return _fi_ar_workspace
-
-
-def get_fi_ar_quant_workspace():
-    return _fi_ar_quant_workspace
-
-
-def initialize_fi_ar_workspace(
+def _create_workspace(
+    backend: str,
     world_size: int,
     rank: int,
     max_token_num: int,
     hidden_dim: int,
     dtype: torch.dtype,
     group: ProcessGroup,
-) -> None:
-    """
-    Initialize the workspace if not already initialized.
-
-    Currently, this function is called by either the AllReduceFusionPass
-    or the FlashInferAllReduce backend for standalone allreduce.
-    If the fusion pass is enabled via
-    --compilation-config.pass_config.fuse_allreduce_rms=true,
-    it will create the workspace first, and the standalone backend
-    will reuse the workspace. Otherwise, the standalone backend will
-    create the workspace.
-    """
-    global _fi_ar_workspace
-    if _fi_ar_workspace is not None:
-        return
-
-    backend = envs.VLLM_FLASHINFER_ALLREDUCE_BACKEND
+):
+    """Create a flashinfer allreduce workspace, returning None on failure."""
     comm_backend = TorchDistBackend(group=group)
     rng_state = random.getstate()
     try:
         random.seed(int.from_bytes(os.urandom(16), byteorder="big"))
-        _fi_ar_workspace = flashinfer_comm.create_allreduce_fusion_workspace(
+        workspace = flashinfer_comm.create_allreduce_fusion_workspace(
             backend=backend,
             world_size=world_size,
             rank=rank,
@@ -81,9 +58,22 @@ def initialize_fi_ar_workspace(
             dtype=dtype,
             comm_backend=comm_backend,
         )
+    except Exception as e:
+        if "multicast" in str(e).lower():
+            logger.warning_once(
+                "Failed to initialize FlashInfer All Reduce workspace: %s. "
+                "This is expected on GPUs without NVSwitch (e.g., NVLink "
+                "bridge-only or PCIe topologies).",
+                e,
+            )
+        else:
+            logger.warning_once(
+                "Failed to initialize FlashInfer All Reduce workspace: %s.",
+                e,
+            )
+        return None
     finally:
         random.setstate(rng_state)
-    assert _fi_ar_workspace is not None
     logger.debug(
         "Initialized FlashInfer All Reduce workspace: backend=%s, "
         "world_size=%d, rank=%d, max_token_num=%d, hidden_dim=%d, dtype=%s",
@@ -94,70 +84,84 @@ def initialize_fi_ar_workspace(
         hidden_dim,
         dtype,
     )
+    return workspace
 
 
-def initialize_fi_ar_quant_workspace(
+def get_fi_ar_workspace(
     world_size: int,
     rank: int,
     max_token_num: int,
     hidden_dim: int,
     dtype: torch.dtype,
     group: ProcessGroup,
-) -> None:
+):
     """
-    Initialize the workspace used by quantization fusion patterns.
+    Return the allreduce workspace for non-quant patterns, initializing if needed.
 
-    Currently this always creates a workspace for trtllm backend as only it
-    supports quantization fusion (FP8/FP4). If the primary workspace
-    is already trtllm, the quant workspace aliases to it.
+    Used by AllReduceFusionPass (non-quant patterns) and FlashInferAllReduce
+    for standalone allreduce. Backend is controlled by
+    VLLM_FLASHINFER_ALLREDUCE_BACKEND env var.
+    """
+    global _fi_ar_workspace
+    if _fi_ar_workspace is not None:
+        return _fi_ar_workspace
+
+    backend = envs.VLLM_FLASHINFER_ALLREDUCE_BACKEND
+
+    # Reuse the quant workspace if it was already created with the same backend
+    if _fi_ar_quant_workspace is not None and _fi_ar_quant_workspace.backend == backend:
+        _fi_ar_workspace = _fi_ar_quant_workspace
+        return _fi_ar_workspace
+
+    _fi_ar_workspace = _create_workspace(
+        backend, world_size, rank, max_token_num, hidden_dim, dtype, group
+    )
+    return _fi_ar_workspace
+
+
+def get_fi_ar_quant_workspace(
+    world_size: int,
+    rank: int,
+    max_token_num: int,
+    hidden_dim: int,
+    dtype: torch.dtype,
+    group: ProcessGroup,
+):
+    """
+    Return the allreduce workspace for quant patterns, initializing if needed.
+
+    Always uses trtllm backend as it is the only one supporting quantization
+    fusion (FP8/FP4).
     """
     global _fi_ar_quant_workspace
     if _fi_ar_quant_workspace is not None:
-        return
+        return _fi_ar_quant_workspace
 
-    # If primary workspace is already trtllm, reuse it
+    # Reuse the non-quant workspace if it was already created with trtllm
     if _fi_ar_workspace is not None and _fi_ar_workspace.backend == "trtllm":
         _fi_ar_quant_workspace = _fi_ar_workspace
-        return
+        return _fi_ar_quant_workspace
 
-    comm_backend = TorchDistBackend(group=group)
-    _fi_ar_quant_workspace = flashinfer_comm.create_allreduce_fusion_workspace(
-        backend="trtllm",
-        world_size=world_size,
-        rank=rank,
-        max_token_num=max_token_num,
-        hidden_dim=hidden_dim,
-        dtype=dtype,
-        comm_backend=comm_backend,
-    )
-    assert _fi_ar_quant_workspace is not None
-    logger.debug(
-        "Initialized FlashInfer All Reduce workspace: backend=trtllm, "
-        "world_size=%d, rank=%d, max_token_num=%d, hidden_dim=%d, dtype=%s",
-        world_size,
-        rank,
-        max_token_num,
-        hidden_dim,
-        dtype,
+    _fi_ar_quant_workspace = _create_workspace(
+        "trtllm", world_size, rank, max_token_num, hidden_dim, dtype, group
     )
+    return _fi_ar_quant_workspace
 
 
 _fi_ar_workspace_lock = threading.Lock()
 
 
 def destroy_fi_ar_workspace():
-    global _fi_ar_workspace
-    global _fi_ar_quant_workspace
+    global _fi_ar_workspace, _fi_ar_quant_workspace
     with _fi_ar_workspace_lock:
-        if (
-            _fi_ar_quant_workspace is not None
-            and _fi_ar_quant_workspace is not _fi_ar_workspace
-        ):
-            _fi_ar_quant_workspace.destroy()
-        _fi_ar_quant_workspace = None
+        is_alias = _fi_ar_workspace is _fi_ar_quant_workspace
+
         if _fi_ar_workspace is not None:
             _fi_ar_workspace.destroy()
-            _fi_ar_workspace = None
+        if _fi_ar_quant_workspace is not None and not is_alias:
+            _fi_ar_quant_workspace.destroy()
+
+        _fi_ar_workspace = _fi_ar_quant_workspace = None
 
 
 atexit.register(destroy_fi_ar_workspace)
@@ -209,13 +213,10 @@ class FlashInferAllReduce:
 
     def _ensure_workspace(self, hidden_dim: int, dtype: torch.dtype) -> bool:
         """Ensure the all reduce workspace is initialized."""
-        if get_fi_ar_workspace() is not None:
-            return True
         if self.max_num_tokens == 0:
             element_size = torch.tensor([], dtype=dtype, device="cpu").element_size()
             self.max_num_tokens = self.max_workspace_size // (hidden_dim * element_size)
-        try:
-            initialize_fi_ar_workspace(
+        workspace = get_fi_ar_workspace(
             world_size=self.world_size,
             rank=self.rank,
             max_token_num=self.max_num_tokens,
@@ -223,15 +224,10 @@ class FlashInferAllReduce:
             dtype=dtype,
             group=self.group,
         )
-            return True
-        except Exception as e:
-            logger.warning(
-                "Failed to initialize FlashInfer All Reduce workspace: %s. "
-                "FlashInfer All Reduce will be disabled.",
-                e,
-            )
+        if workspace is None:
             self.disabled = True
             return False
+        return True
 
     def should_use_fi_ar(self, input_tensor: torch.Tensor) -> bool:
         if self.disabled:
@@ -257,7 +253,15 @@ class FlashInferAllReduce:
         return self._ensure_workspace(hidden_dim, input_tensor.dtype)
 
     def all_reduce(self, input_tensor: torch.Tensor) -> torch.Tensor:
-        workspace = get_fi_ar_workspace()
+        _, hidden_dim = input_tensor.shape
+        workspace = get_fi_ar_workspace(
+            world_size=self.world_size,
+            rank=self.rank,
+            max_token_num=self.max_num_tokens,
+            hidden_dim=hidden_dim,
+            dtype=input_tensor.dtype,
+            group=self.group,
+        )
         return flashinfer_comm.allreduce_fusion(
             input=input_tensor,
             workspace=workspace,