Re: [RFC][PATCH 2/3] CGroups: Use hierarchy_mutex in memory controller

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2008-12-11 10:05:01]:

> On Wed, 10 Dec 2008 16:52:57 -0800
> Paul Menage <menage@google.com> wrote:
> 
> > On Wed, Dec 10, 2008 at 4:49 PM, KAMEZAWA Hiroyuki
> > <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > >
> > >        an operation like rmdir() in somewhere.
> > >                hierarchy_lock for A (acquired)
> > >                hierarchy_lock for B (waiting)
> > >
> > >        in subsys A.
> > >                mmap_sem (acquired)
> > >                hierarchy_lock for A (waiting)
> > >        in subsys B.
> > >                hierarchy_lock for B (aquired)
> > >                mmap_sem             (waiting)
> > >
> > 
> > That's a valid deadlock - you'd need to require the mmap_sem nests
> > either inside all hierarchy_mutexes or else outside all of them.
> > 
> This was a found dead lock between memcg and cpuset.
> 
> another one was 
> 
> 	an operation like rmdir() in somewhere.
> 		hierarchy_lock for memcg (acquired)
> 		hierarchy_lock for B (waiting)
> 
> 	in subsys B.
> 		hierarchy_lock for B (aquired)

But then the hierarchy_locks acquired will be different right?

> 		have to do some memory reclaim -> hierarchy_lock for memcg (waiting)
> 
> I have no objections to hierarchy_lock itself but calling context to memcg is very
> complicated and simple replace of these locks will be just a small help.

Could you please explain the race better?

-- 
	Balbir