On Mon 21-10-19 07:02:55, Naoya Horiguchi wrote: > On Fri, Oct 18, 2019 at 01:52:27PM +0200, Michal Hocko wrote: > > On Thu 17-10-19 16:21:09, Oscar Salvador wrote: > > > From: Naoya Horiguchi <[email protected]> > > > > > > The call to get_user_pages_fast is only to get the pointer to a struct > > > page of a given address, pinning it is memory-poisoning handler's job, > > > so drop the refcount grabbed by get_user_pages_fast > > > > > > Signed-off-by: Naoya Horiguchi <[email protected]> > > > Signed-off-by: Oscar Salvador <[email protected]> > > > --- > > > mm/madvise.c | 24 ++++++++++++------------ > > > 1 file changed, 12 insertions(+), 12 deletions(-) > > > > > > diff --git a/mm/madvise.c b/mm/madvise.c > > > index 2be9f3fdb05e..89ed9a22ff4f 100644 > > > --- a/mm/madvise.c > > > +++ b/mm/madvise.c > > > @@ -878,16 +878,24 @@ static int madvise_inject_error(int behavior, > > > */ > > > order = compound_order(compound_head(page)); > > > > > > - if (PageHWPoison(page)) { > > > - put_page(page); > > > + /* > > > + * The get_user_pages_fast() is just to get the pfn of the > > > + * given address, and the refcount has nothing to do with > > > + * what we try to test, so it should be released immediately. > > > + * This is racy but it's intended because the real hardware > > > + * errors could happen at any moment and memory error handlers > > > + * must properly handle the race. > > > + */ > > > + put_page(page); > > > + > > > + if (PageHWPoison(page)) > > > continue; > > > - } > > > > > > if (behavior == MADV_SOFT_OFFLINE) { > > > pr_info("Soft offlining pfn %#lx at process virtual > > > address %#lx\n", > > > pfn, start); > > > > > > - ret = soft_offline_page(page, MF_COUNT_INCREASED); > > > + ret = soft_offline_page(page, 0); > > > > What does prevent this struct page to go away completely? > > Nothing does it. Memory error handler tries to pin by itself and > then determines what state the page is in now.
OK, but the page is not pinned by this context so it can go away at any time, right? Or do I miss your point? Who would be the Error handler context in this case? -- Michal Hocko SUSE Labs
