[075/212] mm/gup: remove try_get_page(), call try_get_compound_head() directly

Commit Message

Andrew Morton Sept. 2, 2021, 9:53 p.m. UTC

From: John Hubbard <[e-mail]>
Subject: 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/[e-mail]
Signed-off-by: John Hubbard <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Christian Borntraeger <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 arch/s390/mm/fault.c |    2 +-
 fs/pipe.c            |    2 +-
 include/linux/mm.h   |   10 +---------
 mm/gup.c             |   21 +++++++++++++++++----
 4 files changed, 20 insertions(+), 15 deletions(-)

Comments

John Hubbard Sept. 2, 2021, 11:23 p.m. UTC | #1

On 9/2/21 2:53 PM, Andrew Morton wrote:
...
> --- a/mm/gup.c~mm-gup-remove-try_get_page-call-try_get_compound_head-directly
> +++ a/mm/gup.c
> @@ -62,11 +62,24 @@ static void put_page_refs(struct page *p
>   	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 correclty

s/correclty/correctly/

...that is, if it is reasonable to do a typo fixup at this stage in the cycle.


thanks,

Patch

--- a/arch/s390/mm/fault.c~mm-gup-remove-try_get_page-call-try_get_compound_head-directly
+++ a/arch/s390/mm/fault.c
@@ -817,7 +817,7 @@  void do_secure_storage_access(struct pt_
 		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);
--- a/fs/pipe.c~mm-gup-remove-try_get_page-call-try_get_compound_head-directly
+++ a/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);
 
--- a/include/linux/mm.h~mm-gup-remove-try_get_page-call-try_get_compound_head-directly
+++ a/include/linux/mm.h
@@ -1217,15 +1217,7 @@  bool __must_check try_grab_page(struct p
 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)
 {
--- a/mm/gup.c~mm-gup-remove-try_get_page-call-try_get_compound_head-directly
+++ a/mm/gup.c
@@ -62,11 +62,24 @@  static void put_page_refs(struct page *p
 	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 correclty
+ * 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);