Merge branch 'page-refs' (page ref overflow)

[mirror_ubuntu-eoan-kernel.git] / include / linux / mm.h

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 76769749b5a5d546daf7f7513318ad65a494da4c..6b10c21630f54bdd14ddd6efa1510777165ec558 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -966,6 +966,10 @@ static inline bool is_pci_p2pdma_page(const struct page *page)
 }
 #endif /* CONFIG_DEV_PAGEMAP_OPS */
 
+/* 127: arbitrary random number, small enough to assemble well */
+#define page_ref_zero_or_close_to_overflow(page) \
+       ((unsigned int) page_ref_count(page) + 127u <= 127u)
+
 static inline void get_page(struct page *page)
 {
        page = compound_head(page);
@@ -973,8 +977,17 @@ static inline void get_page(struct page *page)
         * Getting a normal page or the head of a compound page
         * requires to already have an elevated page->_refcount.
         */
-       VM_BUG_ON_PAGE(page_ref_count(page) <= 0, page);
+       VM_BUG_ON_PAGE(page_ref_zero_or_close_to_overflow(page), page);
+       page_ref_inc(page);
+}
+
+static inline __must_check bool try_get_page(struct page *page)
+{
+       page = compound_head(page);
+       if (WARN_ON_ONCE(page_ref_count(page) <= 0))
+               return false;
        page_ref_inc(page);
+       return true;
 }
 
 static inline void put_page(struct page *page)