cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug

stable inclusion
from linux-4.19.232
commit 4eec5fe1c680a6c47a9bc0cde00960a4eb663342

--------------------------------

commit 05c7b7a9 upstream.

As previously discussed(https://lkml.org/lkml/2022/1/20/51),
cpuset_attach() is affected with similar cpu hotplug race,
as follow scenario:

     cpuset_attach()				cpu hotplug
    ---------------------------            ----------------------
    down_write(cpuset_rwsem)
    guarantee_online_cpus() // (load cpus_attach)
					sched_cpu_deactivate
					  set_cpu_active()
					  // will change cpu_active_mask
    set_cpus_allowed_ptr(cpus_attach)
      __set_cpus_allowed_ptr_locked()
       // (if the intersection of cpus_attach and
         cpu_active_mask is empty, will return -EINVAL)
    up_write(cpuset_rwsem)

To avoid races such as described above, protect cpuset_attach() call
with cpu_hotplug_lock.

Fixes: be367d09 ("cgroups: let ss->can_attach and ss->attach do whole threadgroups at a time")
Cc: stable@vger.kernel.org # v2.6.32+
Reported-by: NZhao Gongyi <zhaogongyi@huawei.com>
Signed-off-by: NZhang Qiao <zhangqiao22@huawei.com>
Acked-by: NWaiman Long <longman@redhat.com>
Reviewed-by: NMichal Koutný <mkoutny@suse.com>
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>
Signed-off-by: NLaibin Qiu <qiulaibin@huawei.com>

kernel/cgroup/cpuset.c

@@ -1530,6 +1530,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 	cgroup_taskset_first(tset, &css);
 	cs = css_cs(css);
 
+	cpus_read_lock();
 	mutex_lock(&cpuset_mutex);
 
 	/* prepare for attach */
@@ -1585,6 +1586,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 		wake_up(&cpuset_attach_wq);
 
 	mutex_unlock(&cpuset_mutex);
+	cpus_read_unlock();
 }
 
 /* The various types of files and directories in a cpuset file system */