llava: Fix cpu-only clip image encoding sefault (ggml-org#12907)

* llava: Fix cpu-only clip image encoding

* clip : no smart ptr for ggml_backend_t

* Fix for backend_ptr push_back

---------

Co-authored-by: Xuan Son Nguyen <[email protected]>

Author: mattjcly

examples/llava/clip.cpp

@@ -323,36 +323,43 @@ struct clip_ctx {
     std::vector<ggml_backend_t> backend_ptrs;
     std::vector<ggml_backend_buffer_type_t> backend_buft;
 
-    ggml_backend_ptr backend;
-    ggml_backend_ptr backend_cpu;
+    ggml_backend_t backend;
+    ggml_backend_t backend_cpu;
     ggml_backend_buffer_ptr buf;
 
     ggml_backend_sched_ptr sched;
 
     clip_image_size load_image_size;
 
     clip_ctx(clip_context_params & ctx_params) {
-        backend_cpu = ggml_backend_ptr(ggml_backend_init_by_type(GGML_BACKEND_DEVICE_TYPE_CPU, nullptr));
-        backend     = ggml_backend_ptr(ctx_params.use_gpu
+        backend_cpu = ggml_backend_init_by_type(GGML_BACKEND_DEVICE_TYPE_CPU, nullptr);
+        backend     = ctx_params.use_gpu
                         ? ggml_backend_init_by_type(GGML_BACKEND_DEVICE_TYPE_GPU, nullptr)
-                        : nullptr);
+                        : nullptr;
 
         if (backend) {
-            LOG_INF("%s: CLIP using %s backend\n", __func__, ggml_backend_name(backend.get()));
-            backend_ptrs.push_back(backend.get());
-            backend_buft.push_back(ggml_backend_get_default_buffer_type(backend.get()));
+            LOG_INF("%s: CLIP using %s backend\n", __func__, ggml_backend_name(backend));
+            backend_ptrs.push_back(backend);
+            backend_buft.push_back(ggml_backend_get_default_buffer_type(backend));
         } else {
-            backend = std::move(backend_cpu);
+            backend = backend_cpu;
             LOG_INF("%s: CLIP using CPU backend\n", __func__);
         }
 
-        backend_ptrs.push_back(backend_cpu.get());
-        backend_buft.push_back(ggml_backend_get_default_buffer_type(backend_cpu.get()));
+        backend_ptrs.push_back(backend_cpu);
+        backend_buft.push_back(ggml_backend_get_default_buffer_type(backend_cpu));
 
         sched.reset(
             ggml_backend_sched_new(backend_ptrs.data(), backend_buft.data(), backend_ptrs.size(), 8192, false)
         );
     }
+
+    ~clip_ctx() {
+        ggml_backend_free(backend);
+        if (backend != backend_cpu) {
+            ggml_backend_free(backend_cpu);
+        }
+    }
 };
 
 static ggml_cgraph * clip_image_build_graph_siglip(clip_ctx * ctx, const clip_image_f32_batch & imgs) {
@@ -1428,7 +1435,7 @@ struct clip_model_loader {
             }
 
             // alloc memory and offload data
-            ggml_backend_buffer_type_t buft = ggml_backend_get_default_buffer_type(ctx_clip.backend.get());
+            ggml_backend_buffer_type_t buft = ggml_backend_get_default_buffer_type(ctx_clip.backend);
             ctx_clip.buf.reset(ggml_backend_alloc_ctx_tensors_from_buft(ctx_clip.ctx_data.get(), buft));
             ggml_backend_buffer_set_usage(ctx_clip.buf.get(), GGML_BACKEND_BUFFER_USAGE_WEIGHTS);
             for (auto & t : tensors_to_load) {
@@ -2610,7 +2617,7 @@ bool clip_image_batch_encode(clip_ctx * ctx, const int n_threads, const clip_ima
         }
     }
 
-    ggml_backend_cpu_set_n_threads(ctx->backend_cpu.get(), n_threads);
+    ggml_backend_cpu_set_n_threads(ctx->backend_cpu, n_threads);
 
     auto status = ggml_backend_sched_graph_compute(ctx->sched.get(), gf);
     if (status != GGML_STATUS_SUCCESS) {