cpuset: Fix unsafe lock order between cpuset lock and cpuslock

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>

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index d43d25acc95ad582bda4c7985f5165ba9cf0e2dc..153628277a4872884a33f749a32d18e0ed3cb889 100644 (file)
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1528,9 +1528,13 @@ static void cpuset_attach(struct cgroup_taskset *tset)
        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_taskset *tset)
                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_taskset *tset)
                wake_up(&cpuset_attach_wq);
 
        mutex_unlock(&cpuset_mutex);
-       cpus_read_unlock();
 }
 
 /* The various types of files and directories in a cpuset file system */