linux-kernel - Re: [PATCH v4 1/6] cgroup: unify attach permission checking

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Message-ID: <20200120144627.2ttqolx3md6vyfew@wittgenstein>
Date:   Mon, 20 Jan 2020 15:46:28 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org
Subject: Re: [PATCH v4 1/6] cgroup: unify attach permission checking

On Mon, Jan 20, 2020 at 03:42:45PM +0100, Oleg Nesterov wrote:
> I guess I am totally confused, but...
> 
> On 01/17, Christian Brauner wrote:
> >
> > +static inline bool cgroup_same_domain(const struct cgroup *src_cgrp,
> > +				      const struct cgroup *dst_cgrp)
> > +{
> > +	return src_cgrp->dom_cgrp == dst_cgrp->dom_cgrp;
> > +}
> > +
> > +static int cgroup_attach_permissions(struct cgroup *src_cgrp,
> > +				     struct cgroup *dst_cgrp,
> > +				     struct super_block *sb, bool thread)
> > +{
> > +	int ret = 0;
> > +
> > +	ret = cgroup_procs_write_permission(src_cgrp, dst_cgrp, sb);
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = cgroup_migrate_vet_dst(dst_cgrp);
> > +	if (ret)
> > +		return ret;
> > +
> > +	if (thread &&
> > +	    !cgroup_same_domain(src_cgrp->dom_cgrp, dst_cgrp->dom_cgrp))
>                                         ^^^^^^^^^^          ^^^^^^^^^^
> 
>              cgroup_same_domain(src_cgrp, dst_cgrp)
> 
> no?
> 
> And given that cgroup_same_domain() has no other users, perhaps it can
> simply check
> 
> 	     src_cgrp->dom_cgrp != dst_cgrp->dom_cgrp

Yeah, I just added it because the helper is very descriptive given its
name. Maybe too descriptive given my braino.
I'll just remove it in favor of this check and give it a small comment.

Thanks!
Christian