On Mon, Jul 2, 2018 at 11:59 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote:
>
> On Mon 02-07-18 11:27:45, Pavel Tatashin wrote:
> > If struct page is poisoned, and uninitialized access is detected via
> > PF_POISONED_CHECK(page) dump_page() is called to output the page. But,
> > the dump_page() itself accesses struct page to determine how to print
> > it, and therefore gets into a recursive loop.
> >
> > For example:
> > dump_page()
> > __dump_page()
> > PageSlab(page)
> > PF_POISONED_CHECK(page)
> > VM_BUG_ON_PGFLAGS(PagePoisoned(page), page)
> > dump_page() recursion loop.
>
> This deserves a big fat comment in __dump_page. Basically no Page$FOO
> can be used on an HWPoison page.
>
> > Fixes: f165b378bbdf ("mm: uninitialized struct page poisoning sanity checking")
> > Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thank you, I will send out an updated version with a comment.
Pavel
>
> > ---
> > mm/debug.c | 13 +++++++++++--
> > 1 file changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/debug.c b/mm/debug.c
> > index 56e2d9125ea5..469b526e6abc 100644
> > --- a/mm/debug.c
> > +++ b/mm/debug.c
> > @@ -43,12 +43,20 @@ const struct trace_print_flags vmaflag_names[] = {
> >
> > void __dump_page(struct page *page, const char *reason)
> > {
> > + bool page_poisoned = PagePoisoned(page);
> > + int mapcount;
> > +
> > + if (page_poisoned) {
> > + pr_emerg("page:%px is uninitialized and poisoned", page);
> > + goto hex_only;
> > + }
> > +
> > /*
> > * Avoid VM_BUG_ON() in page_mapcount().
> > * page->_mapcount space in struct page is used by sl[aou]b pages to
> > * encode own info.
> > */
> > - int mapcount = PageSlab(page) ? 0 : page_mapcount(page);
> > + mapcount = PageSlab(page) ? 0 : page_mapcount(page);
> >
> > pr_emerg("page:%px count:%d mapcount:%d mapping:%px index:%#lx",
> > page, page_ref_count(page), mapcount,
> > @@ -60,6 +68,7 @@ void __dump_page(struct page *page, const char *reason)
> >
> > pr_emerg("flags: %#lx(%pGp)\n", page->flags, &page->flags);
> >
> > +hex_only:
> > print_hex_dump(KERN_ALERT, "raw: ", DUMP_PREFIX_NONE, 32,
> > sizeof(unsigned long), page,
> > sizeof(struct page), false);
> > @@ -68,7 +77,7 @@ void __dump_page(struct page *page, const char *reason)
> > pr_alert("page dumped because: %s\n", reason);
> >
> > #ifdef CONFIG_MEMCG
> > - if (page->mem_cgroup)
> > + if (!page_poisoned && page->mem_cgroup)
> > pr_alert("page->mem_cgroup:%px\n", page->mem_cgroup);
> > #endif
> > }
> > --
> > 2.18.0
> >
>
> --
> Michal Hocko
> SUSE Labs
>
