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

[Matthew Wilcox]

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@xxxxxxxxxxxxxxxxxxxx/

(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.