kernfs: fix ino wrap-around detection

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

diff --git a/include/linux/mm.h b/include/linux/mm.h
index cf09caeacec12f0c02d103994286eb22d4b2e108..8976f7f1f98886d9466af1a6a0a09c2c54988408 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -561,11 +561,6 @@ static inline void *kvmalloc_array(size_t n, size_t size, gfp_t flags)
 
 extern void kvfree(const void *addr);
 
-static inline atomic_t *compound_mapcount_ptr(struct page *page)
-{
-       return &page[1].compound_mapcount;
-}
-
 static inline int compound_mapcount(struct page *page)
 {
        VM_BUG_ON_PAGE(!PageCompound(page), page);
@@ -836,6 +831,10 @@ static inline bool is_device_public_page(const struct page *page)
 #endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */
 
 
+/* 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);
@@ -843,10 +842,19 @@ 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)
 {
        page = compound_head(page);