mm/gup: remove try_get_page(), call try_get_compound_head() directly

try_get_page() is very similar to try_get_compound_head(), and in fact try_get_page() has fallen a little behind in terms of maintenance: try_get_compound_head() handles speculative page references more thoroughly. There are only two try_get_page() callsites, so just call try_get_compound_head() directly from those, and remove try_get_page() entirely. Also, seeing as how this changes try_get_compound_head() into a non-static function, provide some kerneldoc documentation for it. Link: https://lkml.kernel.org/r/[email protected] Signed-off-by: John Hubbard <[email protected]> Reviewed-by: Christoph Hellwig <[email protected]> Cc: Matthew Wilcox <[email protected]> Cc: Christian Borntraeger <[email protected]> Cc: Heiko Carstens <[email protected]> Cc: Vasily Gorbik <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
dabrace · Sep 3, 2021 · 9857a17 · 9857a17
1 parent 54d516b
commit 9857a17
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Showing 4 changed files with 20 additions and 15 deletions.
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
@@ -817,7 +817,7 @@ void do_secure_storage_access(struct pt_regs *regs)
 		break;
 	case KERNEL_FAULT:
 		page = phys_to_page(addr);
-		if (unlikely(!try_get_page(page)))
+		if (unlikely(!try_get_compound_head(page, 1)))
 			break;
 		rc = arch_make_page_accessible(page);
 		put_page(page);

diff --git a/fs/pipe.c b/fs/pipe.c
@@ -191,7 +191,7 @@ EXPORT_SYMBOL(generic_pipe_buf_try_steal);
  */
 bool generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
 {
-	return try_get_page(buf->page);
+	return try_get_compound_head(buf->page, 1);
 }
 EXPORT_SYMBOL(generic_pipe_buf_get);
 

diff --git a/include/linux/mm.h b/include/linux/mm.h
@@ -1217,15 +1217,7 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags);
 struct page *try_grab_compound_head(struct page *page, int refs,
 				    unsigned int flags);
 
-
-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;
-}
+struct page *try_get_compound_head(struct page *page, int refs);
 
 static inline void put_page(struct page *page)
 {

diff --git a/mm/gup.c b/mm/gup.c
@@ -62,11 +62,24 @@ static void put_page_refs(struct page *page, int refs)
 	put_page(page);
 }
 
-/*
- * Return the compound head page with ref appropriately incremented,
- * or NULL if that failed.
+/**
+ * try_get_compound_head() - return the compound head page with refcount
+ * appropriately incremented, or NULL if that failed.
+ *
+ * This handles potential refcount overflow correctly. It also works correctly
+ * for various lockless get_user_pages()-related callers, due to the use of
+ * page_cache_add_speculative().
+ *
+ * Even though the name includes "compound_head", this function is still
+ * appropriate for callers that have a non-compound @page to get.
+ *
+ * @page:  pointer to page to be gotten
+ * @refs:  the value to add to the page's refcount
+ *
+ * Return: head page (with refcount appropriately incremented) for success, or
+ * NULL upon failure.
  */
-static inline struct page *try_get_compound_head(struct page *page, int refs)
+struct page *try_get_compound_head(struct page *page, int refs)
 {
 	struct page *head = compound_head(page);