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

[Michal Hocko <mhocko@kernel.org>]

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!

> ---
>  mm/memory_hotplug.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> v2:
> - Centralize the check in the add_memory path (David)
> - Instead of failing, add the memory to a nearby node, while warning
>   (and tainting) to call out attention to the firmware bug (Dan)
> 
> v3:
> - Fix the CONFIG_NUMA=n case, and use node 0 as the final fallback (Dan)
> 
> v4:
> - Error out instead of being smart about picking a node that wasn't
>   asked for (Michal)
> 
> v5:
> - Change the return code to -EINVAL (David)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 0a54ffac8c68..e07b80d149db 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1005,6 +1005,11 @@ int __ref add_memory_resource(int nid, struct resource *res)
>  	if (ret)
>  		return ret;
>  
> +	if (!node_possible(nid)) {
> +		WARN(1, "node %d was absent from the node_possible_map\n", nid);
> +		return -EINVAL;
> +	}
> +
>  	mem_hotplug_begin();
>  
>  	/*
> -- 
> 2.21.1

-- 
Michal Hocko
SUSE Labs