Re: [PATCH] cgroup: fix missing cpus_read_{lock,unlock}() in cgroup_transfer_tasks()

[Muchun Song]

> On May 17, 2023, at 15:45, Qi Zheng <qi.zheng@xxxxxxxxx> wrote:
> 
> From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> 
> 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:
> 
> 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>
> 
> So just use the cgroup_attach_{lock,unlock}() helper to fix it.
> 
> Fixes: 4f7e7236435c ("cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock")
> Reported-by: Zhao Gongyi <zhaogongyi@xxxxxxxxxxxxx>
> Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>

Acked-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>

Thanks.