Re: [PATCH 1/1] mm,swapops: Fix compile error on set_pmd_migration_entry.

[wale zhang <wale.zhang.ftd@gmail.com>]

On Thu, Dec 25, 2025 at 6:22 PM Barry Song <21cnbao@gmail.com> wrote:
>
> On Thu, Dec 25, 2025 at 10:41 PM Wale Zhang <wale.zhang.ftd@gmail.com> wrote:
> >
> > ../include/linux/swapops.h: In function ‘set_pmd_migration_entry’:
> > ../include/linux/swapops.h:346:1: error: no return statement in function returning non-void [-Werror=return-type]
> >   346 | }
> >       | ^
> > cc1: some warnings being treated as errors
> >
> > Signed-off-by: Wale Zhang <wale.zhang.ftd@gmail.com>
>
> Sorry. NAK.
>
> This looks odd. We already have a BUILD_BUG(), so no fix is needed.
>
> we should already have:
> ././include/linux/compiler_types.h:631:45: error: call to
> ‘__compiletime_assert_907’ declared with attribute error: BUILD_BUG
> failed
>   631 |         _compiletime_assert(condition, msg,
> __compiletime_assert_, __COUNTER__)
>       |                                             ^
> ././include/linux/compiler_types.h:612:25: note: in definition of
> macro ‘__compiletime_assert’
>   612 |                         prefix ## suffix();
>          \
>       |                         ^~~~~~
>
> Do you actually see this being built? If so, please help identify why it
> gets built.

Hello Barry,

I compile the 6.19-rc2 for arm64 with -O0, this kind of error log will appear.
In file included from /home/wale/repo/linux/master/include/linux/leafops.h:11,
                 from
/home/wale/repo/linux/master/include/linux/userfaultfd_k.h:19,
                 from /home/wale/repo/linux/master/include/linux/mm_inline.h:10,
                 from /home/wale/repo/linux/master/mm/internal.h:13,
                 from /home/wale/repo/linux/master/mm/fadvise.c:24:
/home/wale/repo/linux/master/include/linux/swapops.h: In function
‘set_pmd_migration_entry’:
/home/wale/repo/linux/master/include/linux/swapops.h:346:1: error: no
return statement in function returning non-void [-Werror=return-type]
  346 | }
      | ^
cc1: some warnings being treated as errors
make[4]: *** [/home/wale/repo/linux/master/scripts/Makefile.build:287:
mm/fadvise.o] Error 1
make[4]: *** Waiting for unfinished jobs....

There is an example on my
github(https://github.com/wale-ftd/linux/commits/linux-6.12/) that
used -O0 to compile the 6.12 kernel. If you're interested, you can
check them out.

>
> > ---
> >  include/linux/swapops.h | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/include/linux/swapops.h b/include/linux/swapops.h
> > index 8cfc966eae48..84eb36d97212 100644
> > --- a/include/linux/swapops.h
> > +++ b/include/linux/swapops.h
> > @@ -343,6 +343,7 @@ static inline int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
> >                 struct page *page)
> >  {
> >         BUILD_BUG();
> > +       return 0;
> >  }
> >
> >  static inline void remove_migration_pmd(struct page_vma_mapped_walk *pvmw,
> > --
> > 2.43.0
> >
>
> Thanks
> Barry

--
Thanks
Wale