[PATCH hotfix] mm/zsmalloc: add __maybe_unused attribute for is_first_zpdesc()

[Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>]

Commit c1b3bb73d55e ("mm/zsmalloc: use zpdesc in
trylock_zspage()/lock_zspage()") introduces is_first_zpdesc() function.
However, the function is only used when CONFIG_DEBUG_VM=y.

When building with LLVM=1 and W=1 option, the following warning is
generated:
  $ make -j12 W=1 LLVM=1 mm/zsmalloc.o
  mm/zsmalloc.c:455:20: error: function 'is_first_zpdesc' is not needed and will not be emitted [-Werror,-Wunneeded-internal-declaration]
    455 | static inline bool is_first_zpdesc(struct zpdesc *zpdesc)
        |                    ^~~~~~~~~~~~~~~
  1 error generated.

Fix the warning by adding __maybe_unused attribute to the function.
No functional change intended.

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202501240958.4ILzuBrH-lkp@xxxxxxxxx/
Fixes: c1b3bb73d55e ("mm/zsmalloc: use zpdesc in trylock_zspage()/lock_zspage()")
Signed-off-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
---
 mm/zsmalloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 817626a351f8..6d0e47f7ae33 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -452,7 +452,7 @@ static DEFINE_PER_CPU(struct mapping_area, zs_map_area) = {
 	.lock	= INIT_LOCAL_LOCK(lock),
 };
 
-static inline bool is_first_zpdesc(struct zpdesc *zpdesc)
+static inline bool __maybe_unused is_first_zpdesc(struct zpdesc *zpdesc)
 {
 	return PagePrivate(zpdesc_page(zpdesc));
 }
-- 
2.47.1