Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online_page()

Dan Williams
2019-06-13T00:07:12Z

On Wed, Jun 12, 2019 at 2:47 PM Qian Cai <cai@lca.pw> wrote:
>
> On Wed, 2019-06-12 at 12:38 -0700, Dan Williams wrote:
> > On Wed, Jun 12, 2019 at 12:37 PM Dan Williams <dan.j.williams@intel.com>
> > wrote:
> > >
> > > On Wed, Jun 12, 2019 at 12:16 PM Qian Cai <cai@lca.pw> wrote:
> > > >
> > > > The linux-next commit "mm/sparsemem: Add helpers track active portions
> > > > of a section at boot" [1] causes a crash below when the first kmemleak
> > > > scan kthread kicks in. This is because kmemleak_scan() calls
> > > > pfn_to_online_page(() which calls pfn_valid_within() instead of
> > > > pfn_valid() on x86 due to CONFIG_HOLES_IN_ZONE=n.
> > > >
> > > > The commit [1] did add an additional check of pfn_section_valid() in
> > > > pfn_valid(), but forgot to add it in the above code path.
> > > >
> > > > page:ffffea0002748000 is uninitialized and poisoned
> > > > raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
> > > > raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff
> > > > page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
> > > > ------------[ cut here ]------------
> > > > kernel BUG at include/linux/mm.h:1084!
> > > > invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN PTI
> > > > CPU: 5 PID: 332 Comm: kmemleak Not tainted 5.2.0-rc4-next-20190612+ #6
> > > > Hardware name: Lenovo ThinkSystem SR530 -[7X07RCZ000]-/-[7X07RCZ000]-,
> > > > BIOS -[TEE113T-1.00]- 07/07/2017
> > > > RIP: 0010:kmemleak_scan+0x6df/0xad0
> > > > Call Trace:
> > > > kmemleak_scan_thread+0x9f/0xc7
> > > > kthread+0x1d2/0x1f0
> > > > ret_from_fork+0x35/0x4
> > > >
> > > > [1] https://patchwork.kernel.org/patch/10977957/
> > > >
> > > > Signed-off-by: Qian Cai <cai@lca.pw>
> > > > ---
> > > > include/linux/memory_hotplug.h | 1 +
> > > > 1 file changed, 1 insertion(+)
> > > >
> > > > diff --git a/include/linux/memory_hotplug.h
> > > > b/include/linux/memory_hotplug.h
> > > > index 0b8a5e5ef2da..f02be86077e3 100644
> > > > --- a/include/linux/memory_hotplug.h
> > > > +++ b/include/linux/memory_hotplug.h
> > > > @@ -28,6 +28,7 @@
> > > > unsigned long ___nr = pfn_to_section_nr(___pfn); \
> > > > \
> > > > if (___nr < NR_MEM_SECTIONS && online_section_nr(___nr) && \
> > > > + pfn_section_valid(__nr_to_section(___nr), pfn) && \
> > > > pfn_valid_within(___pfn)) \
> > > > ___page = pfn_to_page(___pfn); \
> > > > ___page; \
> > >
> > > Looks ok to me:
> > >
> > > Acked-by: Dan Williams <dan.j.williams@intel.com>
> > >
> > > ...but why is pfn_to_online_page() a multi-line macro instead of a
> > > static inline like all the helper routines it invokes?
> >
> > I do need to send out a refreshed version of the sub-section patchset,
> > so I'll fold this in and give you a Reported-by credit.
>
> BTW, not sure if your new version will fix those two problem below due to the
> same commit.
>
> https://patchwork.kernel.org/patch/10977957/
>
> 1) offline is busted [1]. It looks like test_pages_in_a_zone() missed the same
> pfn_section_valid() check.

All online memory is to be onlined as a complete section, so I think
the issue is more related to vmemmap_populated() not establishing the
mem_map for all pages in a section.

I take back my suggestions about pfn_valid_within() that operation
should always be scoped to a section when validating online memory.

>
> 2) powerpc booting is generating endless warnings [2]. In vmemmap_populated() at
> arch/powerpc/mm/init_64.c, I tried to change PAGES_PER_SECTION to
> PAGES_PER_SUBSECTION, but it alone seems not enough.

On PowerPC PAGES_PER_SECTION == PAGES_PER_SUBSECTION because the
PowerPC section size was already small. Instead I think the issue is
that PowerPC is partially populating sections, but still expecting
pfn_valid() to succeed. I.e. prior to the subsection patches
pfn_valid() would still work for those holes, but now that it is more
precise it is failing.