[PATCH] kasan: Fix warnings caused by use of arch_enter_lazy_mmu_mode()

[Balbir Singh]

commit c519c3c0a113 ("mm/kasan: avoid lazy MMU mode hazards") introduced
the use of arch_enter_lazy_mmu_mode(), which results in the compiler
complaining about "statement has no effect", when
__HAVE_ARCH_LAZY_MMU_MODE is not defined in include/linux/pgtable.h

The exact warning/error is:

In file included from ./include/linux/kasan.h:37,
from mm/kasan/shadow.c:14:
mm/kasan/shadow.c: In function ‘kasan_populate_vmalloc_pte’:
./include/linux/pgtable.h:247:41: error: statement with no effect [-Werror=unused-value]
247 | #define arch_enter_lazy_mmu_mode() (LAZY_MMU_DEFAULT)
| ^
mm/kasan/shadow.c:322:9: note: in expansion of macro ‘arch_enter_lazy_mmu_mode’
322 | arch_enter_lazy_mmu_mode();
| ^~~~~~~~~~~~~~~~~~~~~~~~

Fix the issue by explicitly casting the use of the function to void,
since the returned state is not forwarded/retained

Fixes: c519c3c0a113 ("mm/kasan: avoid lazy MMU mode hazards")
Signed-off-by: Balbir Singh <bal...@nvidia.com>
---
mm/kasan/shadow.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
index 60b1b72f5ce1..347e02a70892 100644
--- a/mm/kasan/shadow.c
+++ b/mm/kasan/shadow.c
@@ -319,7 +319,7 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
}
spin_unlock(&init_mm.page_table_lock);

- arch_enter_lazy_mmu_mode();
+ (void)arch_enter_lazy_mmu_mode();

return 0;
}
@@ -494,7 +494,7 @@ static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
if (likely(!none))
__free_page(pfn_to_page(pte_pfn(pte)));

- arch_enter_lazy_mmu_mode();
+ (void)arch_enter_lazy_mmu_mode();

return 0;
}
--
2.50.1