linux-kernel - [PATCH 4.19 20/57] cpuset: Fix unsafe lock order between cpuset lock and cpuslock

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Message-Id: <20220321133222.573355878@linuxfoundation.org>
Date:   Mon, 21 Mar 2022 14:52:01 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Michal Koutný <mkoutny@...e.com>,
        Zhang Qiao <zhangqiao22@...wei.com>
Subject: [PATCH 4.19 20/57] cpuset: Fix unsafe lock order between cpuset lock and cpuslock

From: Zhang Qiao <zhangqiao22@...wei.com>

The backport commit 4eec5fe1c680a ("cgroup/cpuset: Fix a race
between cpuset_attach() and cpu hotplug") looks suspicious since
it comes before commit d74b27d63a8b ("cgroup/cpuset: Change
cpuset_rwsem and hotplug lock order") v5.4-rc1~176^2~30 when
the locking order was: cpuset lock, cpus lock.

Fix it with the correct locking order and reduce the cpus locking
range because only set_cpus_allowed_ptr() needs the protection of
cpus lock.

Fixes: 4eec5fe1c680a ("cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug")
Reported-by: Michal Koutný <mkoutny@...e.com>
Signed-off-by: Zhang Qiao <zhangqiao22@...wei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/cgroup/cpuset.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1528,9 +1528,13 @@ static void cpuset_attach(struct cgroup_
 	cgroup_taskset_first(tset, &css);
 	cs = css_cs(css);
 
-	cpus_read_lock();
 	mutex_lock(&cpuset_mutex);
 
+	/*
+	 * It should hold cpus lock because a cpu offline event can
+	 * cause set_cpus_allowed_ptr() failed.
+	 */
+	get_online_cpus();
 	/* prepare for attach */
 	if (cs == &top_cpuset)
 		cpumask_copy(cpus_attach, cpu_possible_mask);
@@ -1549,6 +1553,7 @@ static void cpuset_attach(struct cgroup_
 		cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to);
 		cpuset_update_task_spread_flag(cs, task);
 	}
+       put_online_cpus();
 
 	/*
 	 * Change mm for all threadgroup leaders. This is expensive and may
@@ -1584,7 +1589,6 @@ static void cpuset_attach(struct cgroup_
 		wake_up(&cpuset_attach_wq);
 
 	mutex_unlock(&cpuset_mutex);
-	cpus_read_unlock();
 }
 
 /* The various types of files and directories in a cpuset file system */