tensor-split meta backend fixes (llama/26502)

* backend: propagate buffer usage in meta backend

* ggml-meta: make sure to call init_tensor for all new tensors

* meta: remove explicit check for meta backend in ggml_backend_meta_get_split_state

I can't seem to reproduce the original failure in the latest code.

ggml/src/ggml-backend-impl.h

@@ -83,6 +83,7 @@ extern "C" {
     GGML_API ggml_backend_buffer_t ggml_backend_multi_buffer_alloc_buffer(ggml_backend_buffer_t * buffers, size_t n_buffers);
     GGML_API bool                  ggml_backend_buffer_is_multi_buffer(ggml_backend_buffer_t buffer);
     GGML_API void                  ggml_backend_multi_buffer_set_usage(ggml_backend_buffer_t buffer, enum ggml_backend_buffer_usage usage);
+    GGML_API void                  ggml_backend_meta_buffer_set_usage (ggml_backend_buffer_t buffer, enum ggml_backend_buffer_usage usage);
 
     //
     // Backend (meta)

ggml/src/ggml-backend-meta.cpp

@@ -1118,7 +1118,6 @@ static struct ggml_backend_meta_split_state ggml_backend_meta_get_split_state(
 }
 
 static struct ggml_backend_meta_split_state ggml_backend_meta_get_split_state(const struct ggml_tensor * tensor, bool assume_sync) {
-    GGML_ASSERT(ggml_backend_buffer_is_meta(tensor->buffer));
     ggml_backend_meta_buffer_context * buf_ctx = (ggml_backend_meta_buffer_context *) tensor->buffer->context;
     return ggml_backend_meta_get_split_state(buf_ctx->get_simple_tensor_container(tensor), tensor, assume_sync);
 }
@@ -1178,7 +1177,15 @@ static enum ggml_status ggml_backend_meta_buffer_init_tensor_impl(ggml_backend_m
         t_ij->flags = tensor->flags;
         memcpy(t_ij->op_params, tensor->op_params, sizeof(tensor->op_params));
         ggml_set_name(t_ij, tensor->name);
+
         t_ij->buffer = simple_buf;
+        if (simple_buf) {
+            // the backend that owns the buffer will set .extra
+            ggml_backend_buffer_init_tensor(simple_buf, t_ij);
+        } else {
+            t_ij->extra = tensor->extra;
+        }
+
         t_ij->view_src = tensor->view_src;
         t_ij->view_offs = tensor->view_offs;
         if (t_ij->view_src != nullptr && ggml_backend_buffer_is_meta(t_ij->view_src->buffer)) {
@@ -1209,7 +1216,6 @@ static enum ggml_status ggml_backend_meta_buffer_init_tensor_impl(ggml_backend_m
             t_ij->data = (char *) ggml_backend_buffer_get_base(simple_buf)
                 + size_t(tensor->data) - size_t(ggml_backend_buffer_get_base(tensor->buffer));
         }
-        t_ij->extra = tensor->extra;
         for (int i = 0; i < GGML_MAX_SRC; i++) {
             t_ij->src[i] = tensor->src[i];
             if (tensor->src[i] == tensor) {
@@ -1502,6 +1508,16 @@ bool ggml_backend_buffer_is_meta(ggml_backend_buffer_t buf) {
     return buf != nullptr && buf->iface.free_buffer == ggml_backend_meta_buffer_iface.free_buffer;
 }
 
+void ggml_backend_meta_buffer_set_usage(ggml_backend_buffer_t buffer, enum ggml_backend_buffer_usage usage) {
+    GGML_ASSERT(ggml_backend_buffer_is_meta(buffer));
+    ggml_backend_meta_buffer_context * buf_ctx = (ggml_backend_meta_buffer_context *) buffer->context;
+    for (size_t i = 0; i < buf_ctx->bufs.size(); i++) {
+        if (buf_ctx->bufs[i]) {
+            ggml_backend_buffer_set_usage(buf_ctx->bufs[i].get(), usage);
+        }
+    }
+}
+
 static ggml_backend_buffer_t ggml_backend_meta_buffer_type_alloc_buffer(ggml_backend_buffer_type_t buft, size_t size) {
     const size_t n_simple_bufts = ggml_backend_meta_buft_n_bufts(buft);
 

ggml/src/ggml-backend.cpp

@@ -182,6 +182,8 @@ void ggml_backend_buffer_set_usage(ggml_backend_buffer_t buffer, enum ggml_backe
     // FIXME: add a generic callback to the buffer interface
     if (ggml_backend_buffer_is_multi_buffer(buffer)) {
         ggml_backend_multi_buffer_set_usage(buffer, usage);
+    } else if (ggml_backend_buffer_is_meta(buffer)) {
+        ggml_backend_meta_buffer_set_usage(buffer, usage);
     }
 }