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SubjectRe: [PATCH] Workqueue lockup: Circular dependency in threads
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On 09/05/2017 06:52 PM, Tejun Heo wrote:
> Hello,
>
> On Thu, Aug 31, 2017 at 06:43:56PM +0530, Prateek Sood wrote:
>>> 6) cpuset_mutex is acquired by task init:1 and is waiting for cpuhotplug lock.
>
> Yeah, this is the problematic one.
>
>>> 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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