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

[Yunsheng Lin <linyunsheng@huawei.com>]

On 2019/9/5 15:33, Greg KH wrote:
> On Thu, Sep 05, 2019 at 02:48:24PM +0800, Yunsheng Lin wrote:
>> On 2019/9/5 13:57, Greg KH wrote:
>>> On Thu, Sep 05, 2019 at 09:33:50AM +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 FW does not provide
>>>> the node id and the device has not no parent device.
>>>>
>>>> According to discussion in [1]:
>>>> Even if a device's numa node is not set by fw, the device
>>>> really does belong to a node.
>>>>
>>>> This patch sets the device node to node 0 in device_add() if
>>>> the fw has not specified the node id and it either has no
>>>> parent device, or the parent device also does not have a valid
>>>> node id.
>>>>
>>>> There may be explicit handling out there relying on NUMA_NO_NODE,
>>>> like in nvme_probe().
>>>>
>>>> [1] https://lkml.org/lkml/2019/9/2/466
>>>>
>>>> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
>>>> ---
>>>>  drivers/base/core.c  | 17 ++++++++++++++---
>>>>  include/linux/numa.h |  2 ++
>>>>  2 files changed, 16 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>>>> index 1669d41..466b8ff 100644
>>>> --- a/drivers/base/core.c
>>>> +++ b/drivers/base/core.c
>>>> @@ -2107,9 +2107,20 @@ 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))) {
>>>> +		int nid = parent ? dev_to_node(parent) : NUMA_NO_NODE;
>>>
>>> Can you expand this to be a "real" if statement please?
>>
>> Sure. May I ask why "? :" is not appropriate here?
> 
> Because it is a pain to read, just spell it out and make it obvious what
> is happening.  You write code for developers first, and the compiler
> second, and in this case, either way is identical to the compiler.
> 
>>>> +
>>>> +		if (numa_node_valid(nid)) {
>>>> +			set_dev_node(dev, nid);
>>>> +		} else {
>>>> +			if (nr_node_ids > 1U)
>>>> +				pr_err("device: '%s': has invalid NUMA node(%d)\n",
>>>> +				       dev_name(dev), dev_to_node(dev));
>>>
>>> dev_err() will show you the exact device properly, instead of having to
>>> rely on dev_name().
>>>
>>> And what is a user to do if this message happens?  How do they fix this?
>>> If they can not, what good is this error message?
>>
>> If user know about their system's topology well enough and node 0
>> is not the nearest node to the device, maybe user can readjust that by
>> writing the nearest node to /sys/class/pci_bus/XXXX/device/numa_node,
>> if not, then maybe user need to contact the vendor for info or updates.
>>
>> Maybe print error message as below:
>>
>> dev_err(dev, FW_BUG "has invalid NUMA node(%d). Readjust it by writing to sysfs numa_node or contact your vendor for updates.\n",
>> 	dev_to_node(dev));
> 
> FW_BUG?

The sysfs numa_node writing interface does print FW_BUG error.
Maybe it is a way of telling the user to contact the vendors, which
pushing the vendors to update the FW.

If FW_BUG is too much, there is FW_WARN or FW_INFO.

> 
> Anyway, if you make this change, how many machines start reporting this
> error?  You should also say something like "default node of 0 now
> selected" or something like that, right?

Yes.

> 
> thanks,
> 
> greg k-h
> 
> .
>