Re: [PATCH] cgroup: don't queue css_release_work if one already pending

[Hillf Danton <hdanton@sina.com>]

On Thu, 19 May 2022 22:13:47 -1000 Tejun Heo  wrote:
> On Thu, May 19, 2022 at 04:26:51PM -0700, Tadeusz Struk wrote:
> > On 5/19/22 04:23, Hillf Danton wrote:
> > > On Wed, 18 May 2022 09:48:21 -0700 Tadeusz Struk  wrote:
> > > > On 4/22/22 04:05, Michal Koutny wrote:
> > > > > On Thu, Apr 21, 2022 at 02:00:56PM -1000, Tejun Heo<tj@kernel.org>  wrote:
> > > > > > If this is the case, we need to hold an extra reference to be put by the
> > > > > > css_killed_work_fn(), right?
> > > 
> > > That put could trigger INIT_WORK in css_release() and warning [1]
> > > on init active (active state 0) object OTOH as the same
> > > css->destroy_work is used in both kill and release pathes.
> 
> Hmm... wouldn't the extra reference keep release from happening?

Hm...Hm... have difficulty following up given the risk of memleak without
release.

> 
> > Will this help if there would be two WQs, one for the css_release path
> > and one for the rcu_work?

Unlikely as adding one more queue does not help INIT_WORK.

Hillf
> > 
> > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> > index adb820e98f24..a4873b33e488 100644
> > --- a/kernel/cgroup/cgroup.c
> > +++ b/kernel/cgroup/cgroup.c
> > @@ -124,6 +124,7 @@ DEFINE_PERCPU_RWSEM(cgroup_threadgroup_rwsem);
> >   * which may lead to deadlock.
> >   */
> >  static struct workqueue_struct *cgroup_destroy_wq;
> > +static struct workqueue_struct *cgroup_destroy_rcu_wq;
> 
> I don't understand why this would help. Care to elaborate?
> 
> Thanks.
> 
> -- 
> tejun