A crash on ARM64 in move_freepages_block due to uninitialized pages in reserved memory

[mpatocka@redhat.com (Mikulas Patocka)]

On Thu, 23 Aug 2018, Pasha Tatashin wrote:

> On 8/23/18 7:23 AM, Michal Hocko wrote:
> > On Thu 23-08-18 07:16:34, Mikulas Patocka wrote:
> >>
> >>
> >> On Thu, 23 Aug 2018, Michal Hocko wrote:
> >>
> >>> On Thu 23-08-18 07:02:37, Mikulas Patocka wrote:
> >>> [...]
> >>>> This crash is not from -ENOENT. It crashes because page->compound_head is 
> >>>> 0xffffffffffffffff (see below).
> >>>>
> >>>> If I enable CONFIG_DEBUG_VM, I also get VM_BUG.
> >>>
> >>> This smells like the struct page is not initialized properly. How is
> >>> this memory range added? I mean is it brought up by the memory hotplug
> >>> or during the boot?
> 
> I believe it is due to uninitialized struct pages. Mikulas, could you
> please provide config file, and also the full console output.
> 
> Please make sure that you have:
> CONFIG_DEBUG_VM=y
> CONFIG_ARCH_HAS_DEBUG_VIRTUAL=y
> 
> I wonder what kind of struct page memory layout is used, and also if
> deferred struct pages are enabled or not.

I uploaded configs and console logs (for the real hardware and for the 
virtual machine) here: 
http://people.redhat.com/~mpatocka/testcases/arm64-config/

The virtual machine was running the lvm2 testsuite while the crash 
happened.

> Have you tried bisecting the problem?

I may try some old kernel in the virtual machine to test if the bug 
happens on it.

> Thank you,
> Pavel

Mikulas