Re: [PATCH v5] mm/memory_hotplug: refrain from adding memory into an impossible node

[Michal Hocko <mhocko@kernel.org>]

On Tue 21-04-20 00:14:43, Verma, Vishal L wrote:
> On Fri, 2020-04-17 at 08:38 +0200, Michal Hocko wrote:
> > On Thu 16-04-20 16:54:38, Vishal Verma wrote:
> > > A misbehaving qemu created a situation where the ACPI SRAT table
> > > advertised one fewer proximity domains than intended. The NFIT table did
> > > describe all the expected proximity domains. This caused the device dax
> > > driver to assign an impossible target_node to the device, and when
> > > hotplugged as system memory, this would fail with the following
> > > signature:
> > > 
> > >   [  +0.001627] BUG: kernel NULL pointer dereference, address: 0000000000000088
> > >   [  +0.001331] #PF: supervisor read access in kernel mode
> > >   [  +0.000975] #PF: error_code(0x0000) - not-present page
> > >   [  +0.000976] PGD 80000001767d4067 P4D 80000001767d4067 PUD 10e0c4067 PMD 0
> > >   [  +0.001338] Oops: 0000 [#1] SMP PTI
> > >   [  +0.000676] CPU: 4 PID: 22737 Comm: kswapd3 Tainted: G           O      5.6.0-rc5 #9
> > >   [  +0.001457] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> > >       BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
> > >   [  +0.001990] RIP: 0010:prepare_kswapd_sleep+0x7c/0xc0
> > >   [  +0.000780] Code: 89 df e8 87 fd ff ff 89 c2 31 c0 84 d2 74 e6 0f 1f 44
> > >                       00 00 48 8b 05 fb af 7a 01 48 63 93 88 1d 01 00 48 8b
> > > 		      84 d0 20 0f 00 00 <48> 3b 98 88 00 00 00 75 28 f0 80 a0
> > > 		      80 00 00 00 fe f0 80 a3 38 20
> > >   [  +0.002877] RSP: 0018:ffffc900017a3e78 EFLAGS: 00010202
> > >   [  +0.000805] RAX: 0000000000000000 RBX: ffff8881209e0000 RCX: 0000000000000000
> > >   [  +0.001115] RDX: 0000000000000003 RSI: 0000000000000000 RDI: ffff8881209e0e80
> > >   [  +0.001098] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000008000
> > >   [  +0.001092] R10: 0000000000000000 R11: 0000000000000003 R12: 0000000000000003
> > >   [  +0.001092] R13: 0000000000000003 R14: 0000000000000000 R15: ffffc900017a3ec8
> > >   [  +0.001091] FS:  0000000000000000(0000) GS:ffff888318c00000(0000) knlGS:0000000000000000
> > >   [  +0.001275] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > >   [  +0.000882] CR2: 0000000000000088 CR3: 0000000120b50002 CR4: 00000000001606e0
> > >   [  +0.001095] Call Trace:
> > >   [  +0.000388]  kswapd+0x103/0x520
> > >   [  +0.000494]  ? finish_wait+0x80/0x80
> > >   [  +0.000547]  ? balance_pgdat+0x5a0/0x5a0
> > >   [  +0.000607]  kthread+0x120/0x140
> > >   [  +0.000508]  ? kthread_create_on_node+0x60/0x60
> > >   [  +0.000706]  ret_from_fork+0x3a/0x50
> > > 
> > > Add a check in the add_memory path to fail if the node to which we
> > > are adding memory is in the node_possible_map
> > > 
> > > Cc: Michal Hocko <mhocko@kernel.org>
> > > Cc: David Hildenbrand <david@redhat.com>
> > > Cc: Dan Williams <dan.j.williams@intel.com>
> > > Cc: Dave Hansen <dave.hansen@linux.intel.com>
> > > Acked-by: David Hildenbrand <david@redhat.com>
> > > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> > 
> > Acked-by: Michal Hocko <mhocko@suse.com>
> > 
> > We can start thiking on how to handle such a misconfiguration more
> > gracefully when we see this hitting in real world and find out more why
> > that happens. E.g. if a FW/BIOS are not fixable then we can implement
> > some fallback strategy but this should be a good start.
> > 
> > Thanks!
> 
> Thank you for the review Michal.
> 
> Should this go via Andrew and the mm tree?

Yes, this is the usual route for memory hotplug patches.
-- 
Michal Hocko
SUSE Labs