lkml.org 
[lkml]   [2010]   [Apr]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Patch] workqueue: move lockdep annotations up to destroy_workqueue()
Cong Wang wrote:
> Tejun Heo wrote:
>> 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.
>>
>
> Hmm, it looks like I misunderstand lock_map_acquire()? From the changelog,
> I thought it was added to complain its caller is holding a lock when
> invoking
> it, thus cpu_add_remove_lock is not an exception.
>

Oh, I see, wq->lockdep_map is acquired again in run_workqueue(), so I was wrong. :)
I think you and Oleg are right, the lockdep warning is not irrelevant.

Sorry for the noise, ignore this patch please.

Thanks.


\
 
 \ /
  Last update: 2010-04-01 08:05    [W:3.038 / U:0.556 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site