Re: [PATCH AUTOSEL 4.14 62/95] mm, memory_hotplug: initialize struct pages for the full memory section

[Sasha Levin]

On Tue, May 07, 2019 at 09:31:10AM -0700, Alexander Duyck wrote:
> On Mon, May 6, 2019 at 10:40 PM Sasha Levin <sashal@xxxxxxxxxx> wrote:
> > From: Mikhail Zaslonko <zaslonko@xxxxxxxxxxxxx>
> >
> > [ Upstream commit 2830bf6f05fb3e05bc4743274b806c821807a684 ]
> >
> > If memory end is not aligned with the sparse memory section boundary,
> > the mapping of such a section is only partly initialized.  This may lead
> > to VM_BUG_ON due to uninitialized struct page access from
> > is_mem_section_removable() or test_pages_in_a_zone() function triggered
> > by memory_hotplug sysfs handlers:
> >
> > Here are the the panic examples:
> >  CONFIG_DEBUG_VM=y
> >  CONFIG_DEBUG_VM_PGFLAGS=y
> >
> >  kernel parameter mem=2050M
> >  --------------------------
> >  page:000003d082008000 is uninitialized and poisoned
> >  page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
> >  Call Trace:
> >  ( test_pages_in_a_zone+0xde/0x160)
> >    show_valid_zones+0x5c/0x190
> >    dev_attr_show+0x34/0x70
> >    sysfs_kf_seq_show+0xc8/0x148
> >    seq_read+0x204/0x480
> >    __vfs_read+0x32/0x178
> >    vfs_read+0x82/0x138
> >    ksys_read+0x5a/0xb0
> >    system_call+0xdc/0x2d8
> >  Last Breaking-Event-Address:
> >    test_pages_in_a_zone+0xde/0x160
> >  Kernel panic - not syncing: Fatal exception: panic_on_oops
> >
> >  kernel parameter mem=3075M
> >  --------------------------
> >  page:000003d08300c000 is uninitialized and poisoned
> >  page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
> >  Call Trace:
> >  ( is_mem_section_removable+0xb4/0x190)
> >    show_mem_removable+0x9a/0xd8
> >    dev_attr_show+0x34/0x70
> >    sysfs_kf_seq_show+0xc8/0x148
> >    seq_read+0x204/0x480
> >    __vfs_read+0x32/0x178
> >    vfs_read+0x82/0x138
> >    ksys_read+0x5a/0xb0
> >    system_call+0xdc/0x2d8
> >  Last Breaking-Event-Address:
> >    is_mem_section_removable+0xb4/0x190
> >  Kernel panic - not syncing: Fatal exception: panic_on_oops
> >
> > Fix the problem by initializing the last memory section of each zone in
> > memmap_init_zone() till the very end, even if it goes beyond the zone end.
> >
> > Michal said:
> >
> > : This has alwways been problem AFAIU.  It just went unnoticed because we
> > : have zeroed memmaps during allocation before f7f99100d8d9 ("mm: stop
> > : zeroing memory during allocation in vmemmap") and so the above test
> > : would simply skip these ranges as belonging to zone 0 or provided a
> > : garbage.
> > :
> > : So I guess we do care for post f7f99100d8d9 kernels mostly and
> > : therefore Fixes: f7f99100d8d9 ("mm: stop zeroing memory during
> > : allocation in vmemmap")
> >
> > Link: http://lkml.kernel.org/r/20181212172712.34019-2-zaslonko@xxxxxxxxxxxxx
> > Fixes: f7f99100d8d9 ("mm: stop zeroing memory during allocation in vmemmap")
> > Signed-off-by: Mikhail Zaslonko <zaslonko@xxxxxxxxxxxxx>
> > Reviewed-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>
> > Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx>
> > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>
> > Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>
> > Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> > Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> > Cc: Pasha Tatashin <Pavel.Tatashin@xxxxxxxxxxxxx>
> > Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
> > Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
> > ---
> >  mm/page_alloc.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
>
> Wasn't this patch reverted in Linus's tree for causing a regression on
> some platforms? If so I'm not sure we should pull this in as a
> candidate for stable should we, or am I missing something?

I saw a follow-up patch that should be queued too, but I didn't see that
this one got reverted.

--
Thanks,
Sasha