[PATCH] mm/rmap: Always inline __folio_rmap_sanity_checks()

[Nathan Chancellor <nathan@kernel.org>]

Commit 5e901e249ad1 ("mm/rmap: convert "enum rmap_level" to "enum
pgtable_level"") changed VM_WARN_ON_ONCE, a run time warning, into
BUILD_BUG, a compile time error. After this adjustment, certain builds
with older versions of clang (such as arm64 allmodconfig) started
failing to build with:

  In file included from mm/rmap.c:63:
  In file included from include/linux/ksm.h:14:
  include/linux/rmap.h:440:3: error: call to __compiletime_assert_890 declared with 'error' attribute: BUILD_BUG failed
                  BUILD_BUG();
                  ^
  ...
  <scratch space>:21:1: note: expanded from here
  __compiletime_assert_890
  ^

While __folio_rmap_sanity_checks() is marked 'inline', the compiler may
not always honor it, such as when sanitizers or other instrumentation is
enabled.  If __folio_rmap_sanity_checks() is not inlined, there is no
way the compiler can eliminate the default cause.

Mark __folio_rmap_sanity_checks() as __always_inline to allow the
BUILD_BUG() to work consistently, which clears up the error.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
I assume this will be squashed into
mm-rmap-convert-enum-rmap_level-to-enum-pgtable_level.patch so no fixes
tag.
---
 include/linux/rmap.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 9d40d127bdb7..e8aff6d2deda 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -394,7 +394,7 @@ typedef int __bitwise rmap_t;
 /* The anonymous (sub)page is exclusive to a single process. */
 #define RMAP_EXCLUSIVE		((__force rmap_t)BIT(0))
 
-static inline void __folio_rmap_sanity_checks(const struct folio *folio,
+static __always_inline void __folio_rmap_sanity_checks(const struct folio *folio,
 		const struct page *page, int nr_pages, enum pgtable_level level)
 {
 	/* hugetlb folios are handled separately. */

---
base-commit: 6bee0462de1f9f4fa9400f153d3b0792c20d7111
change-id: 20250814-rmap-fix-build_bug-conversion-90441c036f42

Best regards,
--  
Nathan Chancellor <nathan@kernel.org>