Subject: Re: [PATCH] powerpc/nvdimm: Pick the nearby online node if the device node is not online

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Tue, 16 Jul 2019 09:13:52 +0530

"Aneesh Kumar K.V" <[email-masked]> writes:

> This is similar to what ACPI does. Nvdimm layer doesn't bring the SCM device
> numa node online. Hence we need to make sure we always use an online node
> as ndr_desc.numa_node. Otherwise this result in kernel crashes. The target
> node is used by dax/kmem and that will bring up the numa node online correctly.
>
> Without this patch, we do hit kernel crash as below because we try to access
> uninitialized NODE_DATA in different code paths.
>
> cpu 0x0: Vector: 300 (Data Access) at [c0000000fac53170]
>     pc: c0000000004bbc50: ___slab_alloc+0x120/0xca0
>     lr: c0000000004bc834: __slab_alloc+0x64/0xc0
>     sp: c0000000fac53400
>    msr: 8000000002009033
>    dar: 73e8
>  dsisr: 80000
>   current = 0xc0000000fabb6d80
>   paca    = 0xc000000003870000   irqmask: 0x03   irq_happened: 0x01
>     pid   = 7, comm = kworker/u16:0
> Linux version 5.2.0-06234-g76bd729b2644 (kvaneesh@ltc-boston123) (gcc version 7.4.0 (Ubuntu 7.4.0-1ubuntu1~18.04.1)) #135 SMP Thu Jul 11 05:36:30 CDT 2019
> enter ? for help
> [link register   ] c0000000004bc834 __slab_alloc+0x64/0xc0
> [c0000000fac53400] c0000000fac53480 (unreliable)
> [c0000000fac53500] c0000000004bc818 __slab_alloc+0x48/0xc0
> [c0000000fac53560] c0000000004c30a0 __kmalloc_node_track_caller+0x3c0/0x6b0
> [c0000000fac535d0] c000000000cfafe4 devm_kmalloc+0x74/0xc0
> [c0000000fac53600] c000000000d69434 nd_region_activate+0x144/0x560
> [c0000000fac536d0] c000000000d6b19c nd_region_probe+0x17c/0x370
> [c0000000fac537b0] c000000000d6349c nvdimm_bus_probe+0x10c/0x230
> [c0000000fac53840] c000000000cf3cc4 really_probe+0x254/0x4e0
> [c0000000fac538d0] c000000000cf429c driver_probe_device+0x16c/0x1e0
> [c0000000fac53950] c000000000cf0b44 bus_for_each_drv+0x94/0x130
> [c0000000fac539b0] c000000000cf392c __device_attach+0xdc/0x200
> [c0000000fac53a50] c000000000cf231c bus_probe_device+0x4c/0xf0
> [c0000000fac53a90] c000000000ced268 device_add+0x528/0x810
> [c0000000fac53b60] c000000000d62a58 nd_async_device_register+0x28/0xa0
> [c0000000fac53bd0] c0000000001ccb8c async_run_entry_fn+0xcc/0x1f0
> [c0000000fac53c50] c0000000001bcd9c process_one_work+0x46c/0x860
> [c0000000fac53d20] c0000000001bd4f4 worker_thread+0x364/0x5f0
> [c0000000fac53db0] c0000000001c7260 kthread+0x1b0/0x1c0
> [c0000000fac53e20] c00000000000b954 ret_from_kernel_thread+0x5c/0x68
>
> With the patch we get
>
>  # numactl -H
> available: 2 nodes (0-1)
> node 0 cpus:
> node 0 size: 0 MB
> node 0 free: 0 MB
> node 1 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
> node 1 size: 130865 MB
> node 1 free: 129130 MB
> node distances:
> node   0   1
>   0:  10  20
>   1:  20  10
>  # cat /sys/bus/nd/devices/region0/numa_node
> 0
>  # dmesg | grep papr_scm
> [   91.332305] papr_scm ibm,persistent-memory:ibm,pmemory@44104001: Region registered with target node 2 and online node 0
>
> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
> ---
>  arch/powerpc/platforms/pseries/papr_scm.c | 30 +++++++++++++++++++++--
>  1 file changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index c8ec670ee924..4abb0ecda30a 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -255,12 +255,32 @@ static const struct attribute_group *papr_scm_dimm_groups[] = {
>  	NULL,
>  };
>  
> +static inline int papr_scm_node(int node)
> +{
> +	int min_dist = INT_MAX, dist;
> +	int nid, min_node;
> +
> +	if (node_online(node))
> +		return node;

We should handle NUMA_NO_NODE here.

modified   arch/powerpc/platforms/pseries/papr_scm.c
@@ -260,7 +260,7 @@ static inline int papr_scm_node(int node)
 	int min_dist = INT_MAX, dist;
 	int nid, min_node;
 
-	if (node_online(node))
+	if ((node == NUMA_NO_NODE) || node_online(node))
 		return node;
 
 	min_node = first_online_node;

Will send an updated patch.

> +
> +	min_node = first_online_node;
> +	for_each_online_node(nid) {
> +		dist = node_distance(node, nid);
> +		if (dist < min_dist) {
> +			min_dist = dist;
> +			min_node = nid;
> +		}
> +	}
> +	return min_node;
> +}
> +
>  static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>  {
>  	struct device *dev = &p->pdev->dev;
>  	struct nd_mapping_desc mapping;
>  	struct nd_region_desc ndr_desc;
>  	unsigned long dimm_flags;
> +	int target_nid, online_nid;
>  
>  	p->bus_desc.ndctl = papr_scm_ndctl;
>  	p->bus_desc.module = THIS_MODULE;
> @@ -299,8 +319,11 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>  
>  	memset(&ndr_desc, 0, sizeof(ndr_desc));
>  	ndr_desc.attr_groups = region_attr_groups;
> -	ndr_desc.numa_node = dev_to_node(&p->pdev->dev);
> -	ndr_desc.target_node = ndr_desc.numa_node;
> +	target_nid = dev_to_node(&p->pdev->dev);
> +	online_nid = papr_scm_node(target_nid);
> +	set_dev_node(&p->pdev->dev, online_nid);
> +	ndr_desc.numa_node = online_nid;
> +	ndr_desc.target_node = target_nid;
>  	ndr_desc.res = &p->res;
>  	ndr_desc.of_node = p->dn;
>  	ndr_desc.provider_data = p;
> @@ -318,6 +341,9 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>  				ndr_desc.res, p->dn);
>  		goto err;
>  	}
> +	if (target_nid != online_nid)
> +		dev_info(dev, "Region registered with target node %d and online node %d",
> +			 target_nid, online_nid);
>  
>  	return 0;
>  
> -- 
> 2.21.0