cgroup/cpuset: Wake up cpuset_attach_wq tasks in cpuset_cancel_attach()

stable inclusion
from stable-v4.19.281
commit 30e138e23f43f566b6df87bba51e4d97930671fd
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I715PM
CVE: NA

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

commit ba9182a8 upstream.

After a successful cpuset_can_attach() call which increments the
attach_in_progress flag, either cpuset_cancel_attach() or cpuset_attach()
will be called later. In cpuset_attach(), tasks in cpuset_attach_wq,
if present, will be woken up at the end. That is not the case in
cpuset_cancel_attach(). So missed wakeup is possible if the attach
operation is somehow cancelled. Fix that by doing the wakeup in
cpuset_cancel_attach() as well.

Fixes: e44193d3 ("cpuset: let hotplug propagation work wait for task attaching")
Signed-off-by: NWaiman Long <longman@redhat.com>
Reviewed-by: NMichal Koutný <mkoutny@suse.com>
Cc: stable@vger.kernel.org # v3.11+
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>

kernel/cgroup/cpuset.c

@@ -1588,7 +1588,9 @@ static void cpuset_cancel_attach(struct cgroup_taskset *tset)
 	cs = css_cs(css);
 
 	mutex_lock(&cpuset_mutex);
-	css_cs(css)->attach_in_progress--;
+	cs->attach_in_progress--;
+	if (!cs->attach_in_progress)
+		wake_up(&cpuset_attach_wq);
 	mutex_unlock(&cpuset_mutex);
 }