From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
Cc: LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: [PATCH 5/5] cgroup: fix a race between cgroup_mount() and cgroup_kill_sb()
Date: Tue, 24 Jun 2014 17:01:19 -0400 [thread overview]
Message-ID: <20140624210119.GC14909@htj.dyndns.org> (raw)
In-Reply-To: <53A8D2B8.4080107-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
Hello, Li.
On Tue, Jun 24, 2014 at 09:22:00AM +0800, Li Zefan wrote:
> > Ah, right. Gees, I'm really hating the fact that we have ->mount but
> > not ->umount. However, can't we make it a bit simpler by just
> > introducing a mutex protecting looking up and refing up an existing
> > root and a sb going away? The only problem is that the refcnt being
> > killed isn't atomic w.r.t. new live ref coming up, right? Why not
> > just add a mutex around them so that they can't race?
>
> Well, kill_sb() is called with sb->s_umount held, while kernfs_mount()
> returned with sb->s_umount held, so adding a mutex will lead to ABBA
> deadlock.
Hmmm? Why does that matter? The only region in cgroup_mount() which
needs to be put inside such mutex would be root lookup, no?
Thanks.
--
tejun
next prev parent reply other threads:[~2014-06-24 21:01 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-12 6:31 [PATCH 1/5] cgroup: fix broken css_has_online_children() Li Zefan
2014-06-12 6:32 ` [PATCH 3/5] cgroup: fix mount failure in a corner case Li Zefan
[not found] ` <5399496D.6060003-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2014-06-20 19:10 ` Tejun Heo
2014-06-24 1:15 ` Li Zefan
2014-06-12 6:32 ` [PATCH 4/5] kernfs: introduce kernfs_pin_sb() and kernfs_drop_sb() Li Zefan
[not found] ` <53994943.60703-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2014-06-12 6:31 ` [PATCH 2/5] percpu-ref: introduce percpu_ref_alive() Li Zefan
2014-06-12 6:33 ` [PATCH 5/5] cgroup: fix a race between cgroup_mount() and cgroup_kill_sb() Li Zefan
[not found] ` <539949A1.90301-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2014-06-20 19:35 ` Tejun Heo
[not found] ` <20140620193521.GB28324-9pTldWuhBndy/B6EtB590w@public.gmane.org>
2014-06-24 1:22 ` Li Zefan
[not found] ` <53A8D2B8.4080107-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2014-06-24 21:01 ` Tejun Heo [this message]
[not found] ` <20140624210119.GC14909-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org>
2014-06-25 1:56 ` Li Zefan
2014-06-25 15:00 ` Tejun Heo
[not found] ` <20140625150053.GE26883-Gd/HAXX7CRxy/B6EtB590w@public.gmane.org>
2014-06-27 6:32 ` Li Zefan
[not found] ` <53AD1001.4090405-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2014-06-27 15:00 ` Tejun Heo
2014-06-17 19:26 ` [PATCH 1/5] cgroup: fix broken css_has_online_children() Tejun Heo
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