linux-kernel - Re: [PATCH v4 5/6] clone3: allow spawning processes into cgroups

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Date:   Mon, 20 Jan 2020 22:38:56 +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>, Ingo Molnar <mingo@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Li Zefan <lizefan@...wei.com>,
        Peter Zijlstra <peterz@...radead.org>, cgroups@...r.kernel.org
Subject: Re: [PATCH v4 5/6] clone3: allow spawning processes into cgroups

On Mon, Jan 20, 2020 at 04:39:30PM +0100, Oleg Nesterov wrote:
> On 01/17, Christian Brauner wrote:
> >
> > +static int cgroup_css_set_fork(struct task_struct *parent,
> > +			       struct kernel_clone_args *kargs)
> ...
> > +	kargs->cset = find_css_set(cset, dst_cgrp);
> > +	if (!kargs->cset) {
> > +		ret = -ENOMEM;
> > +		goto err;
> > +	}
> > +
> > +	if (cgroup_is_dead(dst_cgrp)) {
> > +		ret = -ENODEV;
> > +		goto err;
>                 ^^^^^^^^
> 
> this looks wrong... don't we need put_css_set(kargs->cset) before "goto err" ?

Yeah, but we should rather do:

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 4d36255ef25f..482055d1e64a 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5994,6 +5994,8 @@ static int cgroup_css_set_fork(struct kernel_clone_args *kargs)
        if (dst_cgrp)
                cgroup_put(dst_cgrp);
        put_css_set(cset);
+       if (kargs->cset)
+               put_css_set(kargs->cset);
        return ret;
 }

Christian