From: Tejun Heo <tj@kernel.org>
To: Li Zefan <lizefan@huawei.com>
Cc: "Toralf Förster" <toralf.foerster@gmx.de>,
LKML <linux-kernel@vger.kernel.org>,
cgroups <cgroups@vger.kernel.org>
Subject: Re: [PATCH 1/2] cgroup: Delay the clearing of cgrp->kn->priv
Date: Tue, 2 Sep 2014 11:33:01 -0400 [thread overview]
Message-ID: <20140902153301.GA17424@htj.dyndns.org> (raw)
In-Reply-To: <5405A27A.3090605@huawei.com>
Hello, Li.
On Tue, Sep 02, 2014 at 06:56:58PM +0800, Li Zefan wrote:
> for ((; ;))
> {
> echo $$ > /cgroup/sub/cgroup.procs
> ech $$ > /cgce 6f2e0c38c2108a74 ]---
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
copy & paste error?
...
> Reported-by: Toralf Förster <toralf.foerster@gmx.de>
> Signed-off-by: Li Zefan <lizefan@huawei.com>
> ---
>
> Toralf, Thanks for reporting the bug. I'm not able to repy to your email,
> because I was kicked out of the cgroup mailing list so didn't receive
> emails from mailing list for a week.
>
> ---
> kernel/cgroup.c | 19 +++++++++----------
> 1 file changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 1c56924..e03fc62 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -4185,6 +4185,15 @@ static void css_release_work_fn(struct work_struct *work)
>
> mutex_unlock(&cgroup_mutex);
>
> + /*
> + * There are two control paths which try to determine cgroup from
> + * dentry without going through kernfs - cgroupstats_build() and
> + * css_tryget_online_from_dir(). Those are supported by RCU
> + * protecting clearing of cgrp->kn->priv backpointer.
> + */
> + if (!ss && cgroup_parent(cgrp))
> + RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv, NULL);
Can we move the above into the preceding else block? I don't think
holding cgroup_mutex or not makes any difference here. Also, why do
we need the cgroup_parent() check? Do we deref root's kn->priv in the
destruction path? If so, can you please note that in the comment?
Thanks.
--
tejun
next prev parent reply other threads:[~2014-09-02 15:33 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-02 10:56 [PATCH 1/2] cgroup: Delay the clearing of cgrp->kn->priv Li Zefan
2014-09-02 10:57 ` [PATCH 2/2] cgroup: check cgroup liveliness before unbreaking kernfs protection Li Zefan
2014-09-02 15:51 ` Tejun Heo
2014-09-02 15:33 ` Tejun Heo [this message]
2014-09-04 3:35 ` [PATCH 1/2] cgroup: Delay the clearing of cgrp->kn->priv Li Zefan
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