Re: memory offline infinite loop after soft offline

Michal Hocko
2019-10-17T18:28:05Z

On Thu 17-10-19 14:07:13, Qian Cai wrote:
> On Thu, 2019-10-17 at 12:01 +0200, Michal Hocko wrote:
> > On Thu 17-10-19 09:34:10, Naoya Horiguchi wrote:
> > > On Mon, Oct 14, 2019 at 10:39:14AM +0200, Michal Hocko wrote:
> >
> > [...]
> > > > diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> > > > index 89c19c0feadb..5fb3fee16fde 100644
> > > > --- a/mm/page_isolation.c
> > > > +++ b/mm/page_isolation.c
> > > > @@ -274,7 +274,7 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
> > > > * simple way to verify that as VM_BUG_ON(), though.
> > > > */
> > > > pfn += 1 << page_order(page);
> > > > - else if (skip_hwpoisoned_pages && PageHWPoison(page))
> > > > + else if (skip_hwpoisoned_pages && PageHWPoison(compound_head(page)))
> > > > /* A HWPoisoned page cannot be also PageBuddy */
> > > > pfn++;
> > > > else
> > >
> > > This fix looks good to me. The original code only addresses hwpoisoned 4kB-page,
> > > we seem to have this issue since the following commit,
> >
> > Thanks a lot for double checking Naoya!
> >
> > > commit b023f46813cde6e3b8a8c24f432ff9c1fd8e9a64
> > > Author: Wen Congyang <wency@cn.fujitsu.com>
> > > Date: Tue Dec 11 16:00:45 2012 -0800
> > >
> > > memory-hotplug: skip HWPoisoned page when offlining pages
> > >
> > > and extension of LTP coverage finally discovered this.
> >
> > Qian, could you give the patch some testing?
>
> Unfortunately, this does not solve the problem. It looks to me that in
> soft_offline_huge_page(), set_hwpoison_free_buddy_page() will only set
> PG_hwpoison for buddy pages, so the even the compound_head() has no PG_hwpoison
> set.
>
> if (PageBuddy(page_head) && page_order(page_head) >= order) {
> if (!TestSetPageHWPoison(page))
> hwpoisoned = true;

This is more than unexpected. How are we supposed to find out that the
page is poisoned? Any idea Naoya?
--
Michal Hocko
SUSE Labs