Re: [PATCH v19 00/20] Add support for Sub-NUMA cluster (SNC) systems

Reinette Chatre
2024-05-30T17:55:55Z

Hi Tony,

On 5/30/24 9:36 AM, Tony Luck wrote:
> On Wed, May 29, 2024 at 07:46:27PM -0700, Reinette Chatre wrote:
>> Hi Tony,
>>
>> On 5/29/24 1:20 PM, Tony Luck wrote:
>>> On Tue, May 28, 2024 at 03:55:29PM -0700, Reinette Chatre wrote:
>>>> Hi Tony,
>>>>> 13: Wordsmith commit into imperative.
>>>>> I looked at using kobject_has_children() to check for empty
>>>>> directory, but it needs a "struct kobject *" and all I have
>>>>> is "struct kernfs_node *". I'm now checking how many CPUs
>>>>
>>>> Consider how kobject_has_children() uses that struct kobject *.
>>>> Specifically:
>>>> return kobj->sd && kobj->sd->dir.subdirs
>>>>
>>>> It operates on kobj->sd, which is exactly what you have: struct kernfs_node.
>>>
>>> So right. My turn to grumble about other peoples choice of names. If
>>> that field was named "kn" instead of "sd" I would have spotted this
>>> too.
>>>
>>>>> remain in ci->shared_cpu_map to detect whether this is the
>>>>> last SNC node.
>>>>
>>>> hmmm, ok, will take a look ... but please finalize discussion of a patch series
>>>> before submitting a new series that rejects feedback without discussion and
>>>> does something completely different in new version.
>>>
>>> Reinette,
>>>
>>> So here's what rmdir_mondata_subdir_allrdtgrp() looks like using the
>>> subdirs check. It might need an update/better header comment.
>>>
>>> -Tony
>>>
>>> ---
>>>
>>> /*
>>> * Remove all subdirectories of mon_data of ctrl_mon groups
>>> * and monitor groups with given domain id.
>>
>> (note comment still considers that domain id is parameter)
>
> Will fix.
>
>>> */
>>> static void rmdir_mondata_subdir_allrdtgrp(struct rdt_resource *r,
>>> struct rdt_mon_domain *d)
>>> {
>>> struct rdtgroup *prgrp, *crgrp;
>>> struct kernfs_node *kn;
>>> char subname[32];
>>
>> I wonder if static checkers will know that this cannot be used
>> uninitialized?
>
> I wondered that too. There are no complaints from gcc. How do people
> deal with false positives from static checkers? Simplest would be to
> provide an initializer:
>
> char subname[32] = "";
>
> While that might shut up the static check, it would be more confusing
> for human readers.

or char subname[32] = {};

Please elaborate how this will be confusing to human readers? A comment
may help to address that.

I took the time to run a static checker on this series and it did
not complain about this issue. I did not run it with this fixup though, with
just original submission that seem to have similar pattern. I do still think
it would be good to initialize the arrays.

btw ... the static checker I ran did have four other complaints, three about
uninitialized data and one about divide by zero. Most problems appear to be
in mbm_update() that does not initialize rr.sumdomains nor rr.ci before
calling __mon_event_count().

Please use available tools to check code before posting.

>
>>> char name[32];
>>>
>>> sprintf(name, "mon_%s_%02d", r->name, d->ci->id);
>>> if (r->mon_scope != RESCTRL_L3_CACHE) {
>>> /*
>>> * SNC mode: Unless the last domain is being removed must
>>> * just remove the SNC subdomain.
>>> */
>>> sprintf(subname, "mon_sub_%s_%02d", r->name, d->hdr.id);
>>> }
>>>
>>> list_for_each_entry(prgrp, &rdt_all_groups, rdtgroup_list) {
>>> kn = kernfs_find_and_get(prgrp->mon.mon_data_kn, name);
>>> if (!kn)
>>> continue;
>>>
>>> if (kn->dir.subdirs <= 1)
>>> kernfs_remove(kn);
>>> else
>>> kernfs_remove_by_name(kn, subname);
>>>
>>> list_for_each_entry(crgrp, &prgrp->mon.crdtgrp_list, mon.crdtgrp_list) {
>>> kn = kernfs_find_and_get(crgrp->mon.mon_data_kn, name);
>>> if (!kn)
>>> continue;
>>>
>>> if (kn->dir.subdirs <= 1)
>>> kernfs_remove(kn);
>>> else
>>> kernfs_remove_by_name(kn, subname);
>>> }
>>> }
>>> }
>>
>> This solution looks more intuitive to me. I do think that it may be
>> missing some kernfs_put()'s?
>
> There aren't any kernfs_put()'s in the existing code.

Why should it? Existing code does not have the kernfs_put()'s because
the extra reference is only obtained in this new code.

Reinette