Re: kernel panic due to https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2830bf6f05fb3e05bc4743274b806c821807a684

[Michal Hocko]

On Mon 28-01-19 11:37:00, Mikhail Gavrilov wrote:
> > Linus, could you take the revert please?
> >
> > From 817b18d3db36a6900ca9043af8c1416c56358be3 Mon Sep 17 00:00:00 2001
> > From: Michal Hocko <mhocko@xxxxxxxx>
> > Date: Fri, 25 Jan 2019 19:08:58 +0100
> > Subject: [PATCH] Revert "mm, memory_hotplug: initialize struct pages for the
> >  full memory section"
> >
> > This reverts commit 2830bf6f05fb3e05bc4743274b806c821807a684.
> >
> > The underlying assumption that one sparse section belongs into a single
> > numa node doesn't hold really. Robert Shteynfeld has reported a boot
> > failure. The boot log was not captured but his memory layout is as
> > follows:
> > [    0.286954] Early memory node ranges
> > [    0.286955]   node   1: [mem 0x0000000000001000-0x0000000000090fff]
> > [    0.286955]   node   1: [mem 0x0000000000100000-0x00000000dbdf8fff]
> > [    0.286956]   node   1: [mem 0x0000000100000000-0x0000001423ffffff]
> > [    0.286956]   node   0: [mem 0x0000001424000000-0x0000002023ffffff]
> >
> > This means that node0 starts in the middle of a memory section which is
> > also in node1. memmap_init_zone tries to initialize padding of a section
> > even when it is outside of the given pfn range because there are code
> > paths (e.g. memory hotplug) which assume that the full worth of memory
> > section is always initialized. In this particular case, though, such a
> > range is already intialized and most likely already managed by the page
> > allocator. Scribbling over those pages corrupts the internal state and
> > likely blows up when any of those pages gets used.
> >
> > Reported-by: Robert Shteynfeld <robert.shteynfeld@xxxxxxxxx>
> > Fixes: 2830bf6f05fb ("mm, memory_hotplug: initialize struct pages for the full memory section")
> > Cc: stable
> > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> > ---
> >  mm/page_alloc.c | 12 ------------
> >  1 file changed, 12 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index d295c9bc01a8..35fdde041f5c 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -5701,18 +5701,6 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
> >                         cond_resched();
> >                 }
> >         }
> > -#ifdef CONFIG_SPARSEMEM
> > -       /*
> > -        * If the zone does not span the rest of the section then
> > -        * we should at least initialize those pages. Otherwise we
> > -        * could blow up on a poisoned page in some paths which depend
> > -        * on full sections being initialized (e.g. memory hotplug).
> > -        */
> > -       while (end_pfn % PAGES_PER_SECTION) {
> > -               __init_single_page(pfn_to_page(end_pfn), end_pfn, zone, nid);
> > -               end_pfn++;
> > -       }
> > -#endif
> >  }
> >
> >  #ifdef CONFIG_ZONE_DEVICE
> 
> Michal, I suppose that revert the commit
> 2830bf6f05fb3e05bc4743274b806c821807a68 are return my issue
> https://marc.info/?l=linux-mm&m=154499704718428
> Are any other better approach would be proposed for fixing my issue?

As I've said above. We will need to remove the hardcoded
PAGES_PER_SECTION assumption from the hotplug code. Mikhail had a patch
which was dealing with the two specific sysfs file handlers and I will
build on top of that.

-- 
Michal Hocko
SUSE Labs