On 09/05/2017 06:52 PM, Tejun Heo wrote:

Hello,

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

quoted

quoted

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

Yeah, this is the problematic one.

quoted

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.

Thanks for review Tejun

I will send updated patch.

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