[PATCH 5.10 01/80] cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug

Greg Kroah-Hartman
2022-02-28T17:39:04Z

From: Zhang Qiao <zhangqiao22@huawei.com>

commit 05c7b7a92cc87ff8d7fde189d0fade250697573c upstream.

As previously discussed(https://lkml.org/lkml/2022/1/20/51),
cpuset_attach() is affected with similar cpu hotplug race,
as follow scenario:

cpuset_attach() cpu hotplug
--------------------------- ----------------------
down_write(cpuset_rwsem)
guarantee_online_cpus() // (load cpus_attach)
sched_cpu_deactivate
set_cpu_active()
// will change cpu_active_mask
set_cpus_allowed_ptr(cpus_attach)
__set_cpus_allowed_ptr_locked()
// (if the intersection of cpus_attach and
cpu_active_mask is empty, will return -EINVAL)
up_write(cpuset_rwsem)

To avoid races such as described above, protect cpuset_attach() call
with cpu_hotplug_lock.

Fixes: be367d099270 ("cgroups: let ss->can_attach and ss->attach do whole threadgroups at a time")
Cc: stable@vger.kernel.org # v2.6.32+
Reported-by: Zhao Gongyi <zhaogongyi@huawei.com>
Signed-off-by: Zhang Qiao <zhangqiao22@huawei.com>
Acked-by: Waiman Long <longman@redhat.com>
Reviewed-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/cgroup/cpuset.c | 2 ++
1 file changed, 2 insertions(+)

--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2212,6 +2212,7 @@ static void cpuset_attach(struct cgroup_
cgroup_taskset_first(tset, &css);
cs = css_cs(css);

+ cpus_read_lock();
percpu_down_write(&cpuset_rwsem);

/* prepare for attach */
@@ -2267,6 +2268,7 @@ static void cpuset_attach(struct cgroup_
wake_up(&cpuset_attach_wq);

percpu_up_write(&cpuset_rwsem);
+ cpus_read_unlock();
}

/* The various types of files and directories in a cpuset file system */