Re: [syzbot] WARNING in follow_hugetlb_page

Andrew Morton
2022-05-14T01:04:23Z

On Fri, 13 May 2022 16:54:06 -0700 Minchan Kim <minchan@kernel.org> wrote:

> > > >> has been there over a month so I guess it's something else. Does
> > > >> someone have the time to bisect?
> > > >
> > > > I can recreate in my 'easy to debug' environment, so I can bisect in
> > > > parallel with other things I need to do today.
> > > >
> > >
> > > I isolated this to Minchan Kim's "mm: fix is_pinnable_page against on cma
> > > page". Yes, the fat finger fix is in next-20220513.
> > >
> > > I don't have time to analyze right now, but can confirm that in the
> > > reproducer is_pinnable_page is returning false after this change when it
> > > previously returned true.
> >
> > OK, thanks, I dropped mm-fix-is_pinnable_page-against-on-cma-page.patch
>
> Seems like bug of the patch v5 due to change of this
>
> if (mt & (MIGRATE_CMA | MIGRATE_ISOLATE))
>
> The migration type is not bit type so it shold be
>
> if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
>

argh, I meant to check that change but the grey cell died.

I'll bring it back, with

--- a/include/linux/mm.h~mm-fix-is_pinnable_page-against-on-cma-page-fix
+++ a/include/linux/mm.h
@@ -1635,7 +1635,7 @@ static inline bool is_pinnable_page(stru
int __mt = get_pageblock_migratetype(page);
int mt = __READ_ONCE(__mt);

- if (mt & (MIGRATE_CMA | MIGRATE_ISOLATE))
+ if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
return false;
#endif

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