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/20210813044133.1536842-4-jhubbard@nvidia.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index e33c43b..81d7607 100644 (file)
--- 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
index 6d4342b..1fa1f52 100644 (file)
--- 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
index af4845e..d3439dd 100644 (file)
--- 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
index d60419e..1c7f4ec 100644 (file)
--- 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);