Subject: Re: [PATCH v2 2/2] mm: fix initialization of struct page for holes in memory layout

From: Qian Cai <[email-masked]>
Date: Tue, 05 Jan 2021 13:45:37 -0500

On Tue, 2021-01-05 at 10:24 +0200, Mike Rapoport wrote:
> Hi,
> 
> On Mon, Jan 04, 2021 at 02:03:00PM -0500, Qian Cai wrote:
> > On Wed, 2020-12-09 at 23:43 +0200, Mike Rapoport wrote:
> > > From: Mike Rapoport <[email-masked]>
> > > 
> > > Interleave initialization of pages that correspond to holes with the
> > > initialization of memory map, so that zone and node information will be
> > > properly set on such pages.
> > > 
> > > Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions
> > > rather
> > > that check each PFN")
> > > Reported-by: Andrea Arcangeli <[email-masked]>
> > > Signed-off-by: Mike Rapoport <[email-masked]>
> > 
> > Reverting this commit on the top of today's linux-next fixed a crash while
> > reading /proc/kpagecount on a NUMA server.
> 
> Can you please post the entire dmesg?

http://people.redhat.com/qcai/dmesg.txt

> Is it possible to get the pfn that triggered the crash?

Do you have any idea how to convert that fffffffffffffffe to pfn as it is always
that address? I don't understand what that address is though. I tried to catch
it from struct page pointer and page_address() without luck.

>  
> > [ 8858.006726][T99897] BUG: unable to handle page fault for address:
> > fffffffffffffffe
> > [ 8858.014814][T99897] #PF: supervisor read access in kernel mode
> > [ 8858.020686][T99897] #PF: error_code(0x0000) - not-present page
> > [ 8858.026557][T99897] PGD 1371417067 P4D 1371417067 PUD 1371419067 PMD 0 
> > [ 8858.033224][T99897] Oops: 0000 [#1] SMP KASAN NOPTI
> > [ 8858.038710][T99897] CPU: 28 PID: 99897 Comm: proc01 Tainted:
> > G           O      5.11.0-rc1-next-20210104 #1
> > [ 8858.048515][T99897] Hardware name: HPE ProLiant DL385 Gen10/ProLiant
> > DL385 Gen10, BIOS A40 03/09/2018
> > [ 8858.057794][T99897] RIP: 0010:kpagecount_read+0x1be/0x5e0
> > PageSlab at include/linux/page-flags.h:342
> > (inlined by) kpagecount_read at fs/proc/page.c:69