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

[Reinette Chatre]

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