From: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
To: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: shyju pv <shyju.pv-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>,
Sanil kumar <sanil.kumar-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>,
Masanari Iida
<standby24x7-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org,
levinsasha928-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
Subject: Re: [PATCH] cgroup: fix dentry still in use bug when dropping css refs after umount
Date: Tue, 10 Jul 2012 10:11:05 +0800 [thread overview]
Message-ID: <4FFB8F39.9030209@huawei.com> (raw)
In-Reply-To: <20120708063536.GB19021-RcKxWJ4Cfj1J2suj2OqeGauc2jM2gXBXkQQo+JxHRPFibQn6LdNjmg@public.gmane.org>
On 2012/7/8 14:35, Tejun Heo wrote:
> Hello, Li.
>
> On Wed, Jul 04, 2012 at 02:19:15PM +0800, Li Zefan wrote:
>>> I think we're horridly broken for
>>> root cgroup tho - and it has been broken for very long time. I think
>>> it's mostly hidden because most (all?) controllers short-circuit root
>>> cgroup. Eh, well....
>>>
>>
>> Could you elaborate a bit on what's broken for root cgroup?
>
> If someone holds css ref of a root cgroup, AFAICS nothing is
> preventing the cgroup hierarchy from being unmounted and root cgroup
> destroyed.
>
Right, but that should be safe. The css objects of the root cgroup are
allocated at boot, and won't be destroyed at umount.
Furthermore when a cgroup hierarchy is going to be unmounted, those css's
will be made to point to a cgroup named dummytop in rebind_subsystems(),
and there's a syncronize_rcu() in the end of the function, so accessing
css->cgroup is always safe.
In this case, dummytop->dentry is NULL, and that's safe too, because
cgroup_path() is aware of this case.
WARNING: multiple messages have this Message-ID (diff)
From: Li Zefan <lizefan@huawei.com>
To: Tejun Heo <tj@kernel.org>
Cc: shyju pv <shyju.pv@huawei.com>,
Sanil kumar <sanil.kumar@huawei.com>,
Masanari Iida <standby24x7@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Cgroups <cgroups@vger.kernel.org>, <viro@zeniv.linux.org.uk>,
<levinsasha928@gmail.com>
Subject: Re: [PATCH] cgroup: fix dentry still in use bug when dropping css refs after umount
Date: Tue, 10 Jul 2012 10:11:05 +0800 [thread overview]
Message-ID: <4FFB8F39.9030209@huawei.com> (raw)
In-Reply-To: <20120708063536.GB19021@dhcp-172-17-108-109.mtv.corp.google.com>
On 2012/7/8 14:35, Tejun Heo wrote:
> Hello, Li.
>
> On Wed, Jul 04, 2012 at 02:19:15PM +0800, Li Zefan wrote:
>>> I think we're horridly broken for
>>> root cgroup tho - and it has been broken for very long time. I think
>>> it's mostly hidden because most (all?) controllers short-circuit root
>>> cgroup. Eh, well....
>>>
>>
>> Could you elaborate a bit on what's broken for root cgroup?
>
> If someone holds css ref of a root cgroup, AFAICS nothing is
> preventing the cgroup hierarchy from being unmounted and root cgroup
> destroyed.
>
Right, but that should be safe. The css objects of the root cgroup are
allocated at boot, and won't be destroyed at umount.
Furthermore when a cgroup hierarchy is going to be unmounted, those css's
will be made to point to a cgroup named dummytop in rebind_subsystems(),
and there's a syncronize_rcu() in the end of the function, so accessing
css->cgroup is always safe.
In this case, dummytop->dentry is NULL, and that's safe too, because
cgroup_path() is aware of this case.
next prev parent reply other threads:[~2012-07-10 2:11 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-30 7:07 [PATCH] cgroup: fix dentry still in use bug when dropping css refs after umount Li Zefan
2012-06-30 7:07 ` Li Zefan
2012-06-30 14:34 ` Masanari Iida
[not found] ` <4FEEA5CB.8070809-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2012-07-03 17:03 ` Tejun Heo
2012-07-03 17:03 ` Tejun Heo
[not found] ` <20120703170317.GB555-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2012-07-03 22:52 ` Tejun Heo
2012-07-03 22:52 ` Tejun Heo
[not found] ` <20120703225218.GF555-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2012-07-04 6:19 ` Li Zefan
2012-07-04 6:19 ` Li Zefan
[not found] ` <4FF3E063.5010604-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2012-07-08 6:35 ` Tejun Heo
2012-07-08 6:35 ` Tejun Heo
[not found] ` <20120708063536.GB19021-RcKxWJ4Cfj1J2suj2OqeGauc2jM2gXBXkQQo+JxHRPFibQn6LdNjmg@public.gmane.org>
2012-07-10 2:11 ` Li Zefan [this message]
2012-07-10 2:11 ` Li Zefan
[not found] ` <4FFB8F39.9030209-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2012-07-16 16:45 ` Tejun Heo
2012-07-16 16:45 ` Tejun Heo
[not found] ` <4ff55c60.27da440a.65ec.ffff83dfSMTPIN_ADDED@mx.google.com>
[not found] ` <4ff55c60.27da440a.65ec.ffff83dfSMTPIN_ADDED-ATjtLOhZ0NVl57MIdRCFDg@public.gmane.org>
2012-07-07 23:46 ` [PATCH 1/2] Revert "cgroup: superblock can't be released with active dentries" 'Tejun Heo'
2012-07-07 23:46 ` 'Tejun Heo'
[not found] ` <20120707234634.GC16783-RcKxWJ4Cfj1J2suj2OqeGauc2jM2gXBXkQQo+JxHRPFibQn6LdNjmg@public.gmane.org>
2012-07-07 23:46 ` [PATCH 2/2] cgroup: fix cgroup hierarchy umount race 'Tejun Heo'
2012-07-07 23:46 ` 'Tejun Heo'
[not found] ` <20120707234659.GD16783-RcKxWJ4Cfj1J2suj2OqeGauc2jM2gXBXkQQo+JxHRPFibQn6LdNjmg@public.gmane.org>
2012-07-14 12:08 ` Al Viro
2012-07-14 12:08 ` Al Viro
[not found] ` <20120714120852.GK22927-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
2012-07-16 16:44 ` 'Tejun Heo'
2012-07-16 16:44 ` 'Tejun Heo'
2012-07-04 5:56 ` [PATCH] cgroup: fix dentry still in use bug when dropping css refs after umount Li Zefan
2012-07-04 5:56 ` Li Zefan
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