linux-kernel - Re: [PATCH 1/2] cgroup: Set CGRP_RELEASABLE when adding to a cgroup

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Message-ID: <AANLkTimFqJ+qPidS_81DKd7ExSxDG7GNi0gjcUEEq_7j@mail.gmail.com>
Date:	Wed, 24 Nov 2010 15:54:38 -0800
From:	Paul Menage <menage@...gle.com>
To:	Colin Cross <ccross@...roid.com>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	containers@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] cgroup: Set CGRP_RELEASABLE when adding to a cgroup

On Tue, Nov 23, 2010 at 9:37 PM, Colin Cross <ccross@...roid.com> wrote:
> @@ -364,12 +372,8 @@ static void __put_css_set(struct css_set *cg, int taskexit)
>                struct cgroup *cgrp = link->cgrp;
>                list_del(&link->cg_link_list);
>                list_del(&link->cgrp_link_list);
> -               if (atomic_dec_and_test(&cgrp->count) &&
> -                   notify_on_release(cgrp)) {
> -                       if (taskexit)
> -                               set_bit(CGRP_RELEASABLE, &cgrp->flags);
> +               if (atomic_dec_and_test(&cgrp->count))
>                        check_for_release(cgrp);
> -               }

We seem to have lost some notify_on_release() checks - maybe move that
to check_for_release()?
>  /* Caller must verify that the css is not for root cgroup */
> +void __css_get(struct cgroup_subsys_state *css, int count)
> +{
> +       atomic_add(count, &css->refcnt);
> +       set_bit(CGRP_RELEASABLE, &css->cgroup->flags);
> +}

Is css_get() the right place to be putting this? It's not clear to me
why a subsystem taking a refcount on a cgroup's state should render it
releasable when it drops that refcount.

Should we maybe clear the CGRP_RELEASABLE flag right before doing the
userspace callback?

Paul
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