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

[Tejun Heo]

On Wed, May 17, 2023 at 07:45:45AM +0000, Qi Zheng 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>

Applied to cgroupp/for-6.4-fixes w/ Fixes tag updated to 05c7b7a92cc8 (the
commit that 4f7e7236435c fixes) and stable tag added.

Thanks.

-- 
tejun