mm/rmap: always inline __folio_rmap_sanity_checks()

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.

Link: https://lkml.kernel.org/r/20250814-rmap-fix-build_bug-conversion-v1-1-fb7b10a0b362@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 9d40d127bdb780d4354355d5b9a39a5c4e4aa9c4..e8aff6d2deda7280d7b1b0cfd98fd172573958c5 100644 (file)
--- 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. */