Hello,

On Thu, Aug 31, 2017 at 06:43:56PM +0530, Prateek Sood wrote:

quoted

6) cpuset_mutex is acquired by task init:1 and is waiting for cpuhotplug lock.

Yeah, this is the problematic one.

quoted

We can reorder the sequence of locks as in the below diff to avoid this
deadlock. But I am looking for inputs/better solution to fix this deadlock.

---

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
 /**
  * update_tasks_cpumask - Update the cpumasks of tasks in the cpuset.
  * @cs: the cpuset in which each task's cpus_allowed mask needs to be changed

@@ -930,7 +946,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct cpumask *new_cpus)
 	rcu_read_unlock();
 
 	if (need_rebuild_sched_domains)
-		rebuild_sched_domains_locked();
+		rebuild_sched_domains_unlocked()(without taking cpuhotplug.lock)
 }
 
 /**

@@ -1719,6 +1735,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
+	get_online_cpus();
 	mutex_lock(&cpuset_mutex);
 	if (!is_cpuset_online(cs))
 		goto out_unlock;

@@ -1744,6 +1761,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
 	mutex_unlock(&cpuset_mutex);
+	put_online_cpus();
 	kernfs_unbreak_active_protection(of->kn);
 	css_put(&cs->css);
 	flush_workqueue(cpuset_migrate_mm_wq);

And the patch looks good to me.  Can you please format the patch with
proper description and sob?

Thanks.

-- 
tejun