On 08/30/2012 05:17 PM, Tejun Heo wrote:
> Hello, Lai.
>
> On Thu, Aug 30, 2012 at 05:16:01PM +0800, Lai Jiangshan wrote:
>> gcwq_unbind_fn() is unsafe even it is called from a work item.
>> so we need non_manager_role_manager_mutex_unlock().
>>
>> If rebind_workers() is called from a work item, it is safe when there is
>> no CPU_INTENSIVE items. but we can't disable CPU_INTENSIVE items,
>> so it is still unsafe, we need non_manager_role_manager_mutex_unlock() too.
>
> Can you please elaborate? Why is it not safe if there are
> CPU_INTENSIVE items?
>
> Thanks.
>
Imaging there only two workers, they all have UNBOUND bit because the
rebind_workers()
has not been called. The First one is processing work items, the second one is
idle,
when the first one encounter the work item of rebind_workers() and handle it,
at the same
the second one try to create workers and failed and go to process work items
too.
but unlikely the second one encounters a CPU_INTENSIVE items, the nr_running is
still
<=1 after the first one finish rebind_workers().
nr_running.
first one: process work item endless +0 or +1
second one: process the CPU_INTENSIVE item endless +0
No one can service for manager role.
Thanks.
Lai
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