1 files changed, 12 insertions, 0 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index d3df02e76643..116a4164720a 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1623,7 +1623,17 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
          * resources, wait for the previously scheduled operations before
          * proceeding, so that we don't end up keep removing tasks added
          * after execution capability is restored.
+         *
+         * cpuset_hotplug_work calls back into cgroup core via
+         * cgroup_transfer_tasks() and waiting for it from a cgroupfs
+         * operation like this one can lead to a deadlock through kernfs
+         * active_ref protection.  Let's break the protection.  Losing the
+         * protection is okay as we check whether @cs is online after
+         * grabbing cpuset_mutex anyway.  This only happens on the legacy
+         * hierarchies.
          */
+        css_get(&cs->css);
+        kernfs_break_active_protection(of->kn);
         flush_work(&cpuset_hotplug_work);
 
         mutex_lock(&cpuset_mutex);
@@ -1651,6 +1661,8 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
         free_trial_cpuset(trialcs);
 out_unlock:
         mutex_unlock(&cpuset_mutex);
+        kernfs_unbreak_active_protection(of->kn);
+        css_put(&cs->css);
         return retval ?: nbytes;
 }