From: Matthew Wilcox (Oracle) <willy@infradead.org>
Date: Thu, 29 Oct 2020 18:07:47 +0000 (-0400)
Subject: mm: Make page_index() THP-safe
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=refs%2Fheads%2Fnext;p=users%2Fwilly%2Fpagecache.git

mm: Make page_index() THP-safe

You can't dereference page->index for tail pages, so use the head's
index to calculate the offset of this page in the file.  Also move
the function to pagemap.h since it's a pagecache function not used
by the rest of the kernel.  This also makes page_file_offset() work
when called for tail pages.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0c7959ffc3b6e..63264601cdadf 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1555,19 +1555,6 @@ struct address_space *page_file_mapping(struct page *page)
 	return page->mapping;
 }
 
-extern pgoff_t __page_file_index(struct page *page);
-
-/*
- * Return the pagecache index of the passed page.  Regular pagecache pages
- * use ->index whereas swapcache pages use swp_offset(->private)
- */
-static inline pgoff_t page_index(struct page *page)
-{
-	if (unlikely(PageSwapCache(page)))
-		return __page_file_index(page);
-	return page->index;
-}
-
 bool page_mapped(struct page *page);
 struct address_space *page_mapping(struct page *page);
 struct address_space *page_mapping_file(struct page *page);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 3d017559a1ed1..b46c4d222379f 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -449,6 +449,20 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
 			mapping_gfp_mask(mapping));
 }
 
+extern pgoff_t __page_file_index(struct page *page);
+
+/*
+ * Return the pagecache index of the passed page.  Regular pagecache pages
+ * use ->index whereas swapcache pages use swp_offset(->private)
+ */
+static inline pgoff_t page_index(struct page *page)
+{
+	struct page *head = thp_head(page);
+	if (unlikely(PageSwapCache(page)))
+		return __page_file_index(page);
+	return head->index + (page - head);
+}
+
 /* Does this page contain this index? */
 static inline bool thp_contains(struct page *head, pgoff_t index)
 {