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

Greg Kroah-Hartman
2022-03-21T13:59:13Z

From: Zhang Qiao <zhangqiao22@huawei.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@suse.com>
Signed-off-by: Zhang Qiao <zhangqiao22@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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 */