Re: linux-next: build failure after merge of the akpm-current tree

Andrew Morton
2017-09-07T07:46:13Z

On Thu, 7 Sep 2017 15:23:55 +1000 Stephen Rothwell <sfr@canb.auug.org.au> wrote:

> Hi all,
>
> On Wed, 2 Aug 2017 16:31:45 +1000 Stephen Rothwell <sfr@canb.auug.org.au> wrote:
> >
> > On Wed, 2 Aug 2017 15:45:54 +1000 Stephen Rothwell <sfr@canb.auug.org.au> wrote:
> > >
> > > On Tue, 01 Aug 2017 09:08:01 -0400 "Zi Yan" <zi.yan@cs.rutgers.edu> wrote:
> > > >
> > > > I found two possible fixes.
> > > >
> > > > 1. This uses C++ zero initializer, GCC is OK with it.
> > > > I tested with GCC 4.9.3 (has the initialization bug) and GCC 6.4.0.
> > > >
> > > > --- a/include/linux/swapops.h~a
> > > > +++ a/include/linux/swapops.h
> > > > @@ -217,7 +217,7 @@ static inline swp_entry_t pmd_to_swp_ent
> > > >
> > > > static inline pmd_t swp_entry_to_pmd(swp_entry_t entry)
> > > > {
> > > > - return (pmd_t){ 0 };
> > > > + return (pmd_t){};
> > > > }
> > >
> > > I have done that for today ... please decide which is best (or find
> > > something better - maybe every platform really needs to have a __pmd()
> > > definition) and submit a real fix patch to Andrew.
> >
> > OK, that failed for my compiler (gcc 5.2.0) like this:
> >
> > In file included from mm/vmscan.c:55:0:
> > include/linux/swapops.h: In function 'swp_entry_to_pmd':
> > include/linux/swapops.h:226:16: error: empty scalar initializer
> > return (pmd_t){};
> > ^
> > include/linux/swapops.h:226:16: note: (near initialization for '(anonymous)')
>
> This has reappeared today :-( (for the arm multi_v7_defconfig build at
> least)
>
> > So I used the other idea (on top of Andrew's current tree):
>
> The fix patch now looks like this:
>
> From: Stephen Rothwell <sfr@canb.auug.org.au>
> Date: Wed, 2 Aug 2017 15:55:02 +1000
> Subject: [PATCH] mm-thp-enable-thp-migration-in-generic-path-fix-fix
>
> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
> ---
> include/linux/swapops.h | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/swapops.h b/include/linux/swapops.h
> index 45b092aa6419..61cffa148a79 100644
> --- a/include/linux/swapops.h
> +++ b/include/linux/swapops.h
> @@ -223,7 +223,9 @@ static inline swp_entry_t pmd_to_swp_entry(pmd_t pmd)
>
> static inline pmd_t swp_entry_to_pmd(swp_entry_t entry)
> {
> - return (pmd_t){};
> + pmd_t e;
> + memset(&e, 0, sizeof(pmd_t));
> + return e;
> }

err, yeah. I didn't want to add that one :(

At the very least we should add a good comment explaining why we had to
resort to this.