Re: [PATCH] driver core: ensure a device has valid node id in device_add()

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Sep 09, 2019 at 02:04:23PM +0800, Yunsheng Lin wrote:
> Currently a device does not belong to any of the numa nodes
> (dev->numa_node is NUMA_NO_NODE) when the node id is neither
> specified by fw nor by virtual device layer and the device has
> no parent device.

Is this really a problem?

> According to discussion in [1]:
> Even if a device's numa node is not specified, the device really
> does belong to a node.

But as we do not know the node, can we cause more harm by randomly
picking one (i.e. putting it all in node 0)?

> This patch sets the device node to node 0 in device_add() if the
> device's node id is not specified and it either has no parent
> device, or the parent device also does not have a valid node id.
> 
> [1] https://lkml.org/lkml/2019/9/2/466
> 
> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
> ---
> Changelog RFC -> v1:
> 1. Drop log error message and use a "if" instead of "? :".
> 2. Drop the RFC tag.
> ---
>  drivers/base/core.c  | 10 +++++++---
>  include/linux/numa.h |  2 ++
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 1669d41..f79ad20 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -2107,9 +2107,13 @@ int device_add(struct device *dev)
>  	if (kobj)
>  		dev->kobj.parent = kobj;
>  
> -	/* use parent numa_node */
> -	if (parent && (dev_to_node(dev) == NUMA_NO_NODE))
> -		set_dev_node(dev, dev_to_node(parent));
> +	/* use parent numa_node or default node 0 */
> +	if (!numa_node_valid(dev_to_node(dev))) {
> +		if (parent && numa_node_valid(dev_to_node(parent)))
> +			set_dev_node(dev, dev_to_node(parent));
> +		else
> +			set_dev_node(dev, 0);
> +	}

Again, is this going to cause more harm than good?  What happens if we
leave it as "unknown", isn't that better than thinking we "know" it is
in node 0?

thanks,

greg k-h