From mboxrd@z Thu Jan 1 00:00:00 1970 From: Li Zefan Subject: Re: [PATCH 1/2] cgroup: Delay the clearing of cgrp->kn->priv Date: Thu, 4 Sep 2014 11:35:30 +0800 Message-ID: <5407DE02.8090805@huawei.com> References: <5405A27A.3090605@huawei.com> <20140902153301.GA17424@htj.dyndns.org> Mime-Version: 1.0 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20140902153301.GA17424-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="utf-8" To: Tejun Heo Cc: =?UTF-8?B?VG9yYWxmIEbDtnJzdGVy?= , LKML , cgroups =E4=BA=8E 2014/9/2 23:33, Tejun Heo =E5=86=99=E9=81=93: > Hello, Li. >=20 > 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? > ... oops >> Reported-by: Toralf F=C3=B6rster >> Signed-off-by: Li Zefan >> --- >> >> Toralf, Thanks for reporting the bug. I'm not able to repy to your e= mail, >> because I was kicked out of the cgroup mailing list so didn't receiv= e >> 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_s= truct *work) >> =20 >> mutex_unlock(&cgroup_mutex); >> =20 >> + /* >> + * 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); >=20 > Can we move the above into the preceding else block? I don't think > holding cgroup_mutex or not makes any difference here.=20 > Also, why do > we need the cgroup_parent() check? Do we deref root's kn->priv in th= e > destruction path? If so, can you please note that in the comment? >=20 I think the check is not necessary. I was trying to make smaller differ= ence than the original code, and RCU_INIT_POINTER() is in cgroup_rmdir() whi= ch won't be called on root cgroup.