linux-kernel - [PATCH v3 1/4] cgroup/cpuset: Wake up cpuset_attach_wq tasks in cpuset_cancel

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Message-Id: <20230406140404.2718574-2-longman@redhat.com>
Date:   Thu,  6 Apr 2023 10:04:01 -0400
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Christian Brauner <brauner@...nel.org>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Michal Koutný <mkoutny@...e.com>,
        gscrivan@...hat.com, Waiman Long <longman@...hat.com>
Subject: [PATCH v3 1/4] cgroup/cpuset: Wake up cpuset_attach_wq tasks in cpuset_cancel_attach()

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@...hat.com>
Reviewed-by: Michal Koutný <mkoutny@...e.com>
---
 kernel/cgroup/cpuset.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index bc4dcfd7bee5..066689a7dcc3 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2507,11 +2507,15 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
 static void cpuset_cancel_attach(struct cgroup_taskset *tset)
 {
 	struct cgroup_subsys_state *css;
+	struct cpuset *cs;
 
 	cgroup_taskset_first(tset, &css);
+	cs = css_cs(css);
 
 	percpu_down_write(&cpuset_rwsem);
-	css_cs(css)->attach_in_progress--;
+	cs->attach_in_progress--;
+	if (!cs->attach_in_progress)
+		wake_up(&cpuset_attach_wq);
 	percpu_up_write(&cpuset_rwsem);
 }
 
-- 
2.31.1