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

Zi Yan
2022-05-25T10:58:02Z

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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

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