linux-kernel - Re: [PATCH] cgroup: don't queue css_release

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Date:   Thu, 19 May 2022 16:26:51 -0700
From:   Tadeusz Struk <tadeusz.struk@...aro.org>
To:     Hillf Danton <hdanton@...a.com>, Tejun Heo <tj@...nel.org>
Cc:     Michal Koutny <mkoutny@...e.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org,
        syzbot+e42ae441c3b10acf9e9d@...kaller.appspotmail.com
Subject: Re: [PATCH] cgroup: don't queue css_release_work if one already
 pending

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@...nel.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.

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

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;
  
  /* generate an array of cgroup subsystem pointers */
  #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,

-- 
Thanks,
Tadeusz