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Fri, 20 May 2022 01:13:49 -0700 (PDT) Date: Thu, 19 May 2022 22:13:47 -1000 From: Tejun Heo To: Tadeusz Struk Cc: Hillf Danton , Michal Koutny , linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzbot+e42ae441c3b10acf9e9d@syzkaller.appspotmail.com Subject: Re: [PATCH] cgroup: don't queue css_release_work if one already pending Message-ID: References: <20220412192459.227740-1-tadeusz.struk@linaro.org> <20220414164409.GA5404@blackbody.suse.cz> <20220422100400.GA29552@blackbody.suse.cz> <20220519112319.2455-1-hdanton@sina.com> <25fb057a-077f-b601-dcb7-130071c733db@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <25fb057a-077f-b601-dcb7-130071c733db@linaro.org> Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=l5FqNy4I; spf=pass (imf28.hostedemail.com: domain of htejun@gmail.com designates 209.85.210.180 as permitted sender) smtp.mailfrom=htejun@gmail.com; dmarc=fail reason="SPF not aligned (relaxed), DKIM not aligned (relaxed)" header.from=kernel.org (policy=none) X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 09E06C0020 X-Stat-Signature: yjqk6sdnq9tsft7sqy5cgtafijrrdfic X-HE-Tag: 1653034402-990970 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 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? > 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; I don't understand why this would help. Care to elaborate? Thanks. -- tejun