Re: [PATCH] dax/kmem: refrain from adding memory into an impossible node

[David Hildenbrand <david@redhat.com>]

On 11.04.20 02:09, 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 kmem driver to ensure that the target_node for the
> device in question is in the nodes_possible mask.
> 
> Cc: Dan Williams <dan.j.williams@intel.com>
> Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> ---
>  drivers/dax/kmem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 3d0a7e702c94..760c5b4e88c8 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -32,7 +32,7 @@ int dev_dax_kmem_probe(struct device *dev)
>  	 * unavoidable performance issues.
>  	 */
>  	numa_node = dev_dax->target_node;
> -	if (numa_node < 0) {
> +	if (numa_node < 0 || !node_possible(numa_node)) {
>  		dev_warn(dev, "rejecting DAX region %pR with invalid node: %d\n",
>  			 res, numa_node);
>  		return -EINVAL;
> 

I do wonder if we should reject that from
add_memory()..->add_memory_resource() instead, where we do the
__try_online_node().

-- 
Thanks,

David / dhildenb
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