Subject: Re: linux-next: build warning after merge of the mm tree

From: Zi Yan <[email-masked]>
Date: Wed, 25 May 2022 06:57:53 -0400

On 25 May 2022, at 1:54, Stephen Rothwell wrote:

> Hi all,
>
> After merging the mm tree, today's linux-next build (sparc64 defconfig)
> produced this warning:
>
> In file included from include/linux/kernel.h:26,
>                  from include/linux/cpumask.h:10,
>                  from include/linux/smp.h:13,
>                  from include/linux/lockdep.h:14,
>                  from include/linux/spinlock.h:62,
>                  from include/linux/mmzone.h:8,
>                  from include/linux/gfp.h:6,
>                  from include/linux/mm.h:7,
>                  from mm/page_alloc.c:19:
> mm/page_alloc.c: In function 'split_free_page':
> include/linux/minmax.h:20:35: warning: comparison of distinct pointer types lacks a cast
>    20 |         (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
>       |                                   ^~
> include/linux/minmax.h:26:18: note: in expansion of macro '__typecheck'
>    26 |                 (__typecheck(x, y) && __no_side_effects(x, y))
>       |                  ^~~~~~~~~~~
> include/linux/minmax.h:36:31: note: in expansion of macro '__safe_cmp'
>    36 |         __builtin_choose_expr(__safe_cmp(x, y), \
>       |                               ^~~~~~~~~~
> include/linux/minmax.h:45:25: note: in expansion of macro '__careful_cmp'
>    45 | #define min(x, y)       __careful_cmp(x, y, <)
>       |                         ^~~~~~~~~~~~~
> mm/page_alloc.c:1138:35: note: in expansion of macro 'min'
>  1138 |                 free_page_order = min(pfn ? __ffs(pfn) : order, __fls(split_pfn_offset));
>       |                                   ^~~
>
> Introduced by commit
>
>   29a8af92b874 ("mm: fix a potential infinite loop in start_isolate_page_range()")

Hi Stephen,

The patch below should fix it:

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6eec0211e0be..dbbfe4a079d3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1123,7 +1123,9 @@ void split_free_page(struct page *free_page,
             pfn < free_page_pfn + (1UL << order);) {
                int mt = get_pfnblock_migratetype(pfn_to_page(pfn), pfn);

-               free_page_order = min(pfn ? __ffs(pfn) : order, __fls(split_pfn_offset));
+               free_page_order = min_t(unsigned long,
+                                       pfn ? __ffs(pfn) : order,
+                                       __fls(split_pfn_offset));
                __free_one_page(pfn_to_page(pfn), pfn, zone, free_page_order,
                                mt, FPI_NONE);
                pfn += 1UL << free_page_order;

--
Best Regards,
Yan, Zi