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

[Yunsheng Lin <linyunsheng@huawei.com>]

On 2019/9/6 14:52, Greg KH wrote:
> On Fri, Sep 06, 2019 at 02:41:36PM +0800, Yunsheng Lin wrote:
>> 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?
>>>
>>> Anyway, if you make this change, how many machines start reporting this
>>> error? 
>>
>> Any machines with more than one numa node will start reporting this error.
>>
>> 1) many virtual deivces maybe do not set the node id before calling
>>    device_register(), such as vfio, tun, etc.
>>
>> 2) struct cpu has a dev, but does not set the dev' node according to
>>    cpu_to_node().
>>
>> 3) Many platform Device also do not have a node id provided by FW.
> 
> Then this patch is not ok, as you are flooding the kernel log saying the
> system is "broken" when this is just what it always has been like.  How
> is anyone going to "fix" things?

cpu->node_id does not seem to be used, maybe we can fix the cpu device:

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index cc37511d..ad0a841 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -41,7 +41,7 @@ static void change_cpu_under_node(struct cpu *cpu,
        int cpuid = cpu->dev.id;
        unregister_cpu_under_node(cpuid, from_nid);
        register_cpu_under_node(cpuid, to_nid);
-       cpu->node_id = to_nid;
+       set_dev_node(&cpu->dev, to_nid);
 }

 static int cpu_subsys_online(struct device *dev)
@@ -367,7 +367,7 @@ int register_cpu(struct cpu *cpu, int num)
 {
        int error;

-       cpu->node_id = cpu_to_node(num);
+       set_dev_node(&cpu->dev, cpu_to_node(num));
        memset(&cpu->dev, 0x00, sizeof(struct device));
        cpu->dev.id = num;
        cpu->dev.bus = &cpu_subsys;
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index fcb1386..9a6fc51 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -24,7 +24,6 @@ struct device_node;
 struct attribute_group;

 struct cpu {
-       int node_id;            /* The node which contains the CPU */
        int hotpluggable;       /* creates sysfs control file if hotpluggable */
        struct device dev;
 };


> 
> You can adjust the default node to 0 as isn't that what always has
> happened, but you can not claim it is a "error" that this is happening
> because it is not an error, it's just the default operation.

You are right, will remove the error log.