diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h index 2e677e6ad09f..fe4864f7f69c 100644 --- a/include/linux/page_ref.h +++ b/include/linux/page_ref.h @@ -117,7 +117,10 @@ static inline void init_page_count(struct page *page) static inline void page_ref_add(struct page *page, int nr) { - atomic_add(nr, &page->_refcount); + int old_val = atomic_fetch_add(nr, &page->_refcount); + int new_val = old_val + nr; + + VM_BUG_ON_PAGE((unsigned int)new_val < (unsigned int)old_val, page);This seems somewhat weird, as it will trigger not just on overflow, but also if nr is negative. Which I think is valid usage, even though the function has 'add' in name, because 'nr' is signed?
I have not found any places in the mainline kernel where nr is negative in page_ref_add(). I think, by adding this assert we ensure that when 'add' shows up in backtraces it can be assured that the ref count has increased, and if page_ref_sub() showed up it means it decreased. It is strange to have both functions, and yet allow them to do the opposite. We can also change the type to unsigned. Pasha
