Re: + mm-constify-highmem-related-functions-for-improved-const-correctness-fix.patch added to mm-unstable branch

[David Hildenbrand <david@redhat.com>]

On 04.09.25 04:59, Andrew Morton wrote:
> 
> The patch titled
>       Subject: mm-constify-highmem-related-functions-for-improved-const-correctness-fix
> has been added to the -mm mm-unstable branch.  Its filename is
>       mm-constify-highmem-related-functions-for-improved-const-correctness-fix.patch
> 
> This patch will shortly appear at
>       https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-constify-highmem-related-functions-for-improved-const-correctness-fix.patch
> 
> This patch will later appear in the mm-unstable branch at
>      git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> 
> Before you just go and hit "reply", please:
>     a) Consider who else should be cc'ed
>     b) Prefer to cc a suitable mailing list as well
>     c) Ideally: find the original patch on the mailing list and do a
>        reply-to-all to that, adding suitable additional cc's
> 
> *** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
> 
> The -mm tree is included into linux-next via the mm-everything
> branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> and is updated there every 2-3 working days
> 
> ------------------------------------------------------
> From: Andrew Morton <akpm@linux-foundation.org>
> Subject: mm-constify-highmem-related-functions-for-improved-const-correctness-fix
> Date: Wed Sep  3 07:51:59 PM PDT 2025
> 
> nastily "fix" folio_page()
> 
> Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
> Cc: Max Filippov <jcmvbkbc@gmail.com>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>   include/linux/page-flags.h |    4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> --- a/include/linux/page-flags.h~mm-constify-highmem-related-functions-for-improved-const-correctness-fix
> +++ a/include/linux/page-flags.h
> @@ -316,9 +316,9 @@ static __always_inline unsigned long _co
>    * check that the page number lies within @folio; the caller is presumed
>    * to have a reference to the page.
>    */
> -static inline struct page *folio_page(struct folio *folio, unsigned long n)
> +static inline struct page *folio_page(const struct folio *folio, unsigned long n)
>   {
> -	return &folio->page + n;
> +	return (struct page *)(&folio->page + n);
>   }
>   
>   static __always_inline int PageTail(const struct page *page)
> _
> 


I think we should do the following. And I'm wondering if we should squash that
into the relevant nth_page patch instead:

 From 6ada1d36d18969db587ab647757a9538ee1d09a6 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@redhat.com>
Date: Thu, 4 Sep 2025 08:35:24 +0200
Subject: [PATCH] fixup folio_page() const correctness

Signed-off-by: David Hildenbrand <david@redhat.com>
---
  include/linux/page-flags.h | 13 +++++++++----
  1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index faf17ca211b4f..3a9e73abea3e3 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -307,6 +307,12 @@ static __always_inline unsigned long _compound_head(const struct page *page)
  	const struct page *:	(const struct folio *)_compound_head(p), \
  	struct page *:		(struct folio *)_compound_head(p)))
  
+static inline const struct page *_folio_page(const struct folio *folio,
+		unsigned long n)
+{
+	return &folio->page + n;
+}
+
  /**
   * folio_page - Return a page from a folio.
   * @folio: The folio.
@@ -316,10 +322,9 @@ static __always_inline unsigned long _compound_head(const struct page *page)
   * check that the page number lies within @folio; the caller is presumed
   * to have a reference to the page.
   */
-static inline struct page *folio_page(struct folio *folio, unsigned long n)
-{
-	return &folio->page + n;
-}
+#define folio_page(f, n)	(_Generic((f),				\
+	const struct folio *:	(const struct page *)_folio_page(f, n), \
+	struct folio *:		(struct page *)_folio_page(f, n)))
  
  static __always_inline int PageTail(const struct page *page)
  {
-- 
2.50.1


-- 
Cheers

David / dhildenb