From: Waiman Long <longman@redhat.com>
Date: Tue, 11 Apr 2023 09:35:57 -0400
Subject: cgroup/cpuset: Wake up cpuset_attach_wq tasks in
 cpuset_cancel_attach()
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Git-commit: ba9182a89626d5f83c2ee4594f55cb9c1e60f0e2
Patch-mainline: v6.3-rc7
References: bsc#1210827

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: e44193d39e8d ("cpuset: let hotplug propagation work wait for task attaching")
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Michal Koutný <mkoutny@suse.com>
Cc: stable@vger.kernel.org # v3.11+
Signed-off-by: Tejun Heo <tj@kernel.org>
[mkoutny: 4.12: Adjust context]
Acked-by: Michal Koutný <mkoutny@suse.com>
---
 kernel/cgroup/cpuset.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1508,7 +1508,9 @@ static void cpuset_cancel_attach(struct
 	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);
 }