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SubjectRe: [Patch] workqueue: move lockdep annotations up to destroy_workqueue()
Hello,

On 04/01/2010 01:28 PM, Cong Wang wrote:
>> Hmmm... can you please try to see whether this circular locking
>> warning involving wq->lockdep_map is reproducible w/ the bonding
>> locking fixed? I still can't see where wq -> cpu_add_remove_lock
>> dependency is created.
>>
>
> I thought this is obvious.
>
> Here it is:
>
> void destroy_workqueue(struct workqueue_struct *wq)
> {
> const struct cpumask *cpu_map = wq_cpu_map(wq);
> int cpu;
>
> cpu_maps_update_begin(); <----------------- Hold
> cpu_add_remove_lock here
> spin_lock(&workqueue_lock);
> list_del(&wq->list);
> spin_unlock(&workqueue_lock);
>
> for_each_cpu(cpu, cpu_map)
> cleanup_workqueue_thread(per_cpu_ptr(wq->cpu_wq, cpu));
> <------ See below
> cpu_maps_update_done(); <----------------- Release
> cpu_add_remove_lock here
>
> ...
> static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
> {
> /*
> * Our caller is either destroy_workqueue() or CPU_POST_DEAD,
> * cpu_add_remove_lock protects cwq->thread.
> */
> if (cwq->thread == NULL)
> return;
>
> lock_map_acquire(&cwq->wq->lockdep_map); <-------------- Lockdep
> complains here.
> lock_map_release(&cwq->wq->lockdep_map);
> ...

Yeap, the above is cpu_add_remove_lock -> wq->lockdep_map dependency.
I can see that but I'm failing to see where the dependency the other
direction is created.

Thanks.

--
tejun


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