pipebuffer: Ensure refcounts of live buffer objects are never zero.

src/gallium/auxiliary/pipebuffer/pb_buffer.h

@@ -177,12 +177,16 @@ pb_get_base_buffer( struct pb_buffer *buf,
 }
 
 
+/**
+ * Don't call this directly. Use pb_reference instead.
+ */
 static INLINE void 
 pb_destroy(struct pb_buffer *buf)
 {
    assert(buf);
    if(!buf)
       return;
+   assert(buf->base.refcount == 0);
    buf->vtbl->destroy(buf);
 }
 
@@ -193,11 +197,16 @@ static INLINE void
 pb_reference(struct pb_buffer **dst,
              struct pb_buffer *src)
 {
-   if (src) 
+   if (src) {
+      assert(src->base.refcount);
       src->base.refcount++;
+   }
 
-   if (*dst && --(*dst)->base.refcount == 0)
-      pb_destroy( *dst );
+   if (*dst) {
+      assert((*dst)->base.refcount);
+      if(--(*dst)->base.refcount == 0)
+         pb_destroy( *dst );
+   }
 
    *dst = src;
 }

src/gallium/auxiliary/pipebuffer/pb_bufmgr_fenced.c

@@ -86,8 +86,7 @@ fenced_bufmgr_create_buffer(struct pb_manager *mgr,
    
    fenced_buf = fenced_buffer_create(fenced_mgr->fenced_list, buf);
    if(!fenced_buf) {
-      assert(buf->base.refcount == 1);
-      pb_destroy(buf);
+      pb_reference(&buf, NULL);
    }
    
    return fenced_buf;