Re: [RFC][PATCH -mmotm 3/4] memcg: avoid dead lock caused by racebetween oom and cpuset_attach

[Daisuke Nishimura]

On Fri, 5 Dec 2008 22:27:10 +0900 (JST)
"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:

> Daisuke Nishimura said:
> > mpol_rebind_mm(), which can be called from cpuset_attach(), does
> > down_write(mm->mmap_sem).
> > This means down_write(mm->mmap_sem) can be called under cgroup_mutex.
> >
> > OTOH, page fault path does down_read(mm->mmap_sem) and calls
> > mem_cgroup_try_charge_xxx(),
> > which may eventually calls mem_cgroup_out_of_memory(). And
> > mem_cgroup_out_of_memory()
> > calls cgroup_lock().
> > This means cgroup_lock() can be called under down_read(mm->mmap_sem).
> >
> good catch.
> 
Thanks.

> > If those two paths race, dead lock can happen.
> >
> > This patch avoid this dead lock by:
> >   - remove cgroup_lock() from mem_cgroup_out_of_memory().
> agree to this.
> 
> >   - define new mutex (memcg_tasklist) and serialize mem_cgroup_move_task()
> >     (->attach handler of memory cgroup) and mem_cgroup_out_of_memory.
> >
> Hmm...seems temporal fix (and adding new global lock...)
> But ok, we need fix. revist this later.
> 
I agree.

> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxx,com>
> 
Thank you.


Daisuke Nishimura.
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