[PATCH] mm: swap: make free_swap_and_cache()/swapcache_prepare() inline functions

[PATCH] mm: swap: make free_swap_and_cache()/swapcache_prepare() inline functions

[Arnd Bergmann]

We get a build warning from a boolean expression that is never used:

mm/madvise.c: In function 'madvise_free_pte_range':
include/linux/swap.h:490:55: error: value computed is not used [-Werror=unused-value]
 #define free_swap_and_cache(e) (is_migration_entry(e) || is_device_private_entry(e))
                                                       ^~
mm/madvise.c:353:4: note: in expansion of macro 'free_swap_and_cache'
    free_swap_and_cache(entry);

This changes the two macros to a compound expression that gcc does
not warn about. Changing them to inline functions would have been
nicer but is not possible here because that would introduce a recursive
header file dependency.

Fixes: mmotm ("mm/ZONE_DEVICE: new type of ZONE_DEVICE for unaddressable memory")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 include/linux/swap.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 2be396acdf48..8a807292037f 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -487,8 +487,8 @@ static inline void show_swap_cache_info(void)
 {
 }
 
-#define free_swap_and_cache(e) (is_migration_entry(e) || is_device_private_entry(e))
-#define swapcache_prepare(e) (is_migration_entry(e) || is_device_private_entry(e))
+#define free_swap_and_cache(e) ({(is_migration_entry(e) || is_device_private_entry(e));})
+#define swapcache_prepare(e) ({(is_migration_entry(e) || is_device_private_entry(e));})
 
 static inline int add_swap_count_continuation(swp_entry_t swp, gfp_t gfp_mask)
 {
-- 
2.9.0

Re: [PATCH] mm: swap: make free_swap_and_cache()/swapcache_prepare() inline functions

[Jerome Glisse]

On Wed, Aug 23, 2017 at 03:31:42PM +0200, Arnd Bergmann wrote:
> We get a build warning from a boolean expression that is never used:
> 
> mm/madvise.c: In function 'madvise_free_pte_range':
> include/linux/swap.h:490:55: error: value computed is not used [-Werror=unused-value]
>  #define free_swap_and_cache(e) (is_migration_entry(e) || is_device_private_entry(e))
>                                                        ^~
> mm/madvise.c:353:4: note: in expansion of macro 'free_swap_and_cache'
>     free_swap_and_cache(entry);
> 
> This changes the two macros to a compound expression that gcc does
> not warn about. Changing them to inline functions would have been
> nicer but is not possible here because that would introduce a recursive
> header file dependency.
> 
> Fixes: mmotm ("mm/ZONE_DEVICE: new type of ZONE_DEVICE for unaddressable memory")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Thanks for taking care of that.

Reviewed-by: Jérôme Glisse <jglisse@redhat.com>