On Mon, Aug 15, 2022 at 01:27:38PM -1000, Tejun Heo wrote:

Bringing up a CPU may involve creating new tasks which requires read-locking
threadgroup_rwsem, so threadgroup_rwsem nests inside cpus_read_lock().
However, cpuset's ->attach(), which may be called with thredagroup_rwsem
write-locked, also wants to disable CPU hotplug and acquires
cpus_read_lock(), leading to a deadlock.

Fix it by guaranteeing that ->attach() is always called with CPU hotplug
disabled and removing cpus_read_lock() call from cpuset_attach().

Signed-off-by: Tejun Heo <redacted>

Applied to cgroup/for-6.0-fixes w/ commit message and comment update
suggested by Xuewen and Fixes / stable tags added.

Thanks.

-- 
tejun