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Subject: Re: [PATCH] cgroup: fix missing cpus_read_{lock,unlock}() in
 cgroup_transfer_tasks()
From:   Muchun Song <muchun.song@linux.dev>
In-Reply-To: <20230517074545.2045035-1-qi.zheng@linux.dev>
Date:   Wed, 17 May 2023 15:51:56 +0800
Cc:     Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Qi Zheng <zhengqi.arch@bytedance.com>,
        Zhao Gongyi <zhaogongyi@bytedance.com>
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Message-Id: <75E872A8-652F-40B0-80D0-378569E77775@linux.dev>
References: <20230517074545.2045035-1-qi.zheng@linux.dev>
To:     Qi Zheng <qi.zheng@linux.dev>
Precedence: bulk


> On May 17, 2023, at 15:45, Qi Zheng <qi.zheng@linux.dev> wrote:
>=20
> From: Qi Zheng <zhengqi.arch@bytedance.com>
>=20
> The commit 4f7e7236435c ("cgroup: Fix threadgroup_rwsem <-> =
cpus_read_lock()
> deadlock") fixed the deadlock between cgroup_threadgroup_rwsem and
> cpus_read_lock() by introducing cgroup_attach_{lock,unlock}() and =
removing
> cpus_read_{lock,unlock}() from cpuset_attach(). But =
cgroup_transfer_tasks()
> was missed and not handled, which will cause th following warning:
>=20
> WARNING: CPU: 0 PID: 589 at kernel/cpu.c:526 =
lockdep_assert_cpus_held+0x32/0x40
> CPU: 0 PID: 589 Comm: kworker/1:4 Not tainted 6.4.0-rc2-next-20230517 =
#50
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 =
04/01/2014
> Workqueue: events cpuset_hotplug_workfn
> RIP: 0010:lockdep_assert_cpus_held+0x32/0x40
> <...>
> Call Trace:
>  <TASK>
>  cpuset_attach+0x40/0x240
>  cgroup_migrate_execute+0x452/0x5e0
>  ? _raw_spin_unlock_irq+0x28/0x40
>  cgroup_transfer_tasks+0x1f3/0x360
>  ? find_held_lock+0x32/0x90
>  ? cpuset_hotplug_workfn+0xc81/0xed0
>  cpuset_hotplug_workfn+0xcb1/0xed0
>  ? process_one_work+0x248/0x5b0
>  process_one_work+0x2b9/0x5b0
>  worker_thread+0x56/0x3b0
>  ? process_one_work+0x5b0/0x5b0
>  kthread+0xf1/0x120
>  ? kthread_complete_and_exit+0x20/0x20
>  ret_from_fork+0x1f/0x30
>  </TASK>
>=20
> So just use the cgroup_attach_{lock,unlock}() helper to fix it.
>=20
> Fixes: 4f7e7236435c ("cgroup: Fix threadgroup_rwsem <-> =
cpus_read_lock() deadlock")
> Reported-by: Zhao Gongyi <zhaogongyi@bytedance.com>
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>

Acked-by: Muchun Song <songmuchun@bytedance.com>

Thanks.