Re: [PATCH] mm/gup: check page posion status for coredump.

Aili Yao
2021-03-18T05:35:32Z

On Thu, 18 Mar 2021 04:46:00 +0000
Matthew Wilcox <willy@infradead.org> wrote:

> On Wed, Mar 17, 2021 at 10:12:02AM +0100, David Hildenbrand wrote:
> > > + if (IS_ENABLED(CONFIG_MEMORY_FAILURE) && ret == 1) {
> > > + if (unlikely(PageHuge(page) && PageHWPoison(compound_head(page))))
> > > + ret = 0;
> > > + else if (unlikely(PageHWPoison(page)))
> > > + ret = 0;
> > > + }
> >
> > I wonder if a simple
> >
> > if (PageHWPoison(compound_head(page)))
> > ret = 0;
> >
> > won't suffice. But I guess the "issue" is compound pages that are not huge
> > pages or transparent huge pages.
>
> THPs don't set the HWPoison bit on the head page.
>
> https://lore.kernel.org/linux-mm/20210316140947.GA3420@casper.infradead.org/
>
> (and PAGEFLAG(HWPoison, hwpoison, PF_ANY))
>
> By the way,
>
> #ifdef CONFIG_MEMORY_FAILURE
> PAGEFLAG(HWPoison, hwpoison, PF_ANY)
> TESTSCFLAG(HWPoison, hwpoison, PF_ANY)
> #define __PG_HWPOISON (1UL << PG_hwpoison)
> extern bool take_page_off_buddy(struct page *page);
> #else
> PAGEFLAG_FALSE(HWPoison)
> #define __PG_HWPOISON 0
> #endif
>
> so there's no need for this
> if (IS_ENABLED(CONFIG_MEMORY_FAILURE)
> check, as it simply turns into
>
> if (PageHuge(page) && 0)
> else if (0)
>
> and the compiler can optimise it all away.

Yes, You are right, I will modify this later.
Thanks for correction

--
Thanks!
Aili Yao