linux-kernel - Re: [PATCH RFC] driver core: ensure a device has valid node id in device

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Date:   Thu, 5 Sep 2019 11:02:49 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Yunsheng Lin <linyunsheng@...wei.com>
Cc:     rafael@...nel.org, linux-kernel@...r.kernel.org,
        peterz@...radead.org, mingo@...nel.org, mhocko@...nel.org,
        linuxarm@...wei.com
Subject: Re: [PATCH RFC] driver core: ensure a device has valid node id in
 device_add()

On Thu, Sep 05, 2019 at 04:57:00PM +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@...wei.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.

But is this always going to be caused by a firmware bug?  If so, ok, if
not, and it's a driver/bus kernel issue, we should not say this.

thanks,

greg k-h