metal : avoid call free for non-owned buffer

Author: jhen0409

ggml/src/ggml-metal/ggml-metal-device.m

@@ -817,6 +817,7 @@ bool ggml_metal_device_supports_op(ggml_metal_device_t dev, const struct ggml_te
 
     // if false, the Metal buffer data is allocated in private GPU memory and is not shared with the host
     bool is_shared;
+    bool owned;
 
     // multiple buffers are used only to avoid the maximum buffer size limitation when using mmap
     int n_buffers;
@@ -949,6 +950,7 @@ ggml_metal_buffer_t ggml_metal_buffer_init(ggml_metal_device_t dev, size_t size,
     if (shared) {
         res->all_data = ggml_metal_host_malloc(size_aligned);
         res->is_shared = true;
+        res->owned = true;
     } else {
         // dummy, non-NULL value - we'll populate this after creating the Metal buffer below
         res->all_data = (void *) 0x000000400ULL;
@@ -1007,6 +1009,7 @@ ggml_metal_buffer_t ggml_metal_buffer_map(ggml_metal_device_t dev, void * ptr, s
     res->all_size = size;
 
     res->is_shared = true;
+    res->owned = false;
 
     res->n_buffers = 0;
 
@@ -1100,7 +1103,7 @@ void ggml_metal_buffer_free(ggml_metal_buffer_t buf) {
 
     ggml_metal_buffer_rset_free(buf);
 
-    if (buf->is_shared) {
+    if (buf->is_shared && buf->owned) {
 #if TARGET_OS_OSX
         vm_deallocate((vm_map_t)mach_task_self(), (vm_address_t)buf->all_data, buf->all_size);
 #else