| Date | Tue, 26 Oct 2021 20:48:59 +0100 | From | Matthew Wilcox <> | Subject | Re: [RFC 1/8] mm: add overflow and underflow checks for page->_refcount |
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On Tue, Oct 26, 2021 at 05:38:15PM +0000, Pasha Tatashin wrote: > static inline void page_ref_add(struct page *page, int nr) > { > - atomic_add(nr, &page->_refcount); > + int ret; > + > + VM_BUG_ON(nr <= 0); > + ret = atomic_add_return(nr, &page->_refcount); > + VM_BUG_ON_PAGE(ret <= 0, page);
This isn't right. _refcount is allowed to overflow into the negatives. See page_ref_zero_or_close_to_overflow() and the conversations that led to it being added.
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