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

From: Yunsheng Lin <linyunsheng@huawei.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: <rafael@kernel.org>, <linux-kernel@vger.kernel.org>,
	<peterz@infradead.org>, <mingo@kernel.org>, <mhocko@kernel.org>,
	<linuxarm@huawei.com>
Subject: Re: [PATCH RFC] driver core: ensure a device has valid node id in device_add()
Date: Thu, 5 Sep 2019 14:48:24 +0800	[thread overview]
Message-ID: <e5905af2-5a8d-7b00-d2a6-a961f3eee120@huawei.com> (raw)
In-Reply-To: <20190905055727.GB23826@kroah.com>

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?

> 
>> +
>> +		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));

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