On Mon, May 17, 2021 at 12:12:50PM +0200, Oscar Salvador wrote:
> On Mon, May 17, 2021 at 01:54:00PM +0900, Naoya Horiguchi wrote:
> > From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> >
> > When hugetlb page fault (under overcommitting situation) and
> > memory_failure() race, VM_BUG_ON_PAGE() is triggered by the following race:
> >
> > CPU0: CPU1:
> >
> > gather_surplus_pages()
> > page = alloc_surplus_huge_page()
> > memory_failure_hugetlb()
> > get_hwpoison_page(page)
> > __get_hwpoison_page(page)
> > get_page_unless_zero(page)
> > zero = put_page_testzero(page)
> > VM_BUG_ON_PAGE(!zero, page)
> > enqueue_huge_page(h, page)
> > put_page(page)
> >
> > __get_hwpoison_page() only checks page refcount before taking additional
> ^^ the? ^^ an
> > one for memory error handling, which is wrong because there's a time
> > window where compound pages have non-zero refcount during initialization.
> >
> > So makes __get_hwpoison_page() check page status a bit more for a few
> ^^ make
> > types of compound pages. PageSlab() check is added because otherwise
> > "non anonymous thp" path is wrongly chosen.
>
> This is no longer true with this patch, is it? What happened here?
Sorry, we need remove this. I dropped the changes for PageSlab
because I'm still not sure about what to do (I'd like to do it
in a separate work).
>
> > static int __get_hwpoison_page(struct page *page)
> > {
> > struct page *head = compound_head(page);
> > + int ret = 0;
> > +
> > +#ifdef CONFIG_HUGETLB_PAGE
> > + spin_lock(&hugetlb_lock);
> > + if (PageHuge(head) && (HPageFreed(head) || HPageMigratable(head)))
> > + ret = get_page_unless_zero(head);
> > + spin_unlock(&hugetlb_lock);
> > + if (ret > 0)
> > + return ret;
> > +#endif
>
> I am kind of fine with this, but I wonder whether it makes sense to hide this
> details into helper (with an empty stub for non-hugetlb pages)?
OK, I will do this.
>
> > if (!PageHuge(head) && PageTransHuge(head)) {
> This !PageHuge could go?
I'll update this, too.
Thanks,
Naoya Horiguchi
