Re: [PATCH] mm: Provide consistent declaration for num_poisoned_pages

[Guenter Roeck]

On 02/26/2018 03:57 PM, David Rientjes wrote:
> On Mon, 26 Feb 2018, Guenter Roeck wrote:
>
> > clang reports the following compile warning.
> >
> > In file included from mm/vmscan.c:56:
> > ./include/linux/swapops.h:327:22: warning:
> > 	section attribute is specified on redeclared variable [-Wsection]
> > extern atomic_long_t num_poisoned_pages __read_mostly;
> >                       ^
> > ./include/linux/mm.h:2585:22: note: previous declaration is here
> > extern atomic_long_t num_poisoned_pages;
> >                       ^
> >
> > Let's use __read_mostly everywhere.
> >
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > Cc: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
> > ---
> >   include/linux/mm.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index ad06d42adb1a..bd4bd59f02c1 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -2582,7 +2582,7 @@ extern int get_hwpoison_page(struct page *page);
> >   extern int sysctl_memory_failure_early_kill;
> >   extern int sysctl_memory_failure_recovery;
> >   extern void shake_page(struct page *p, int access);
> > -extern atomic_long_t num_poisoned_pages;
> > +extern atomic_long_t num_poisoned_pages __read_mostly;
> >   extern int soft_offline_page(struct page *page, int flags);
> >   
> >   
>
> No objection to the patch, of course, but I'm wondering if it's (1) the
> only such clang compile warning for mm/, and (2) if the re-declaration in

It is the only one I recall seeing in mm/ while testing the clang/retpoline
changes with ToT clang 7.0.0, but then I didn't pay too close attention.

> mm.h could be avoided by including swapops.h?

Another alternative would be to remove the extern fom swapops.h and have
swapops.h include mm.h instead. I chose the least invasive change since
I didn't want to risk breaking some other build (after all, maybe there
was a reason for declaring num_poisoned_pages in two include files).

Guenter