Re: [PATCH 04/10 V4] workqueue: add manage_workers_slowpath()

[Tejun Heo]

Hello, Lai.

On Sun, Sep 02, 2012 at 12:28:22AM +0800, Lai Jiangshan wrote:
> If hotplug code grabbed the manager_mutex and worker_thread try to create
> a worker, the manage_worker() will return false and worker_thread go to
> process work items. Now, on the CPU, all workers are processing work items,
> no idle_worker left/ready for managing. It breaks the concept of workqueue
> and it is bug.
> 
> So when manage_worker() failed to grab the manager_mutex, it should
> try to enter normal process contex and then compete on the manager_mutex
> instead of return false.
> 
> To safely do this, we add manage_workers_slowpath() and the worker
> go to process work items mode to do the managing jobs. thus
> managing jobs are processed via work item and can free to compete
> on manager_mutex.

Ummm.... this seems overly complicated.  How about scheduling rebind
work to a worker and forcing it to break out of the work processing
loop?  I think it can be done fairly easily using POOL_MANAGE_WORKERS
- set it from the rebind function, break out of work processing loop
if it's set, replace need_to_manage_workers() with POOL_MANAGE_WORKERS
test (the function really isn't necessary) and always jump back to
recheck afterwards.  It might need a bit more mangling here and there
but that should be the essence of it.  I'll give a stab at it later
today.

Thanks.

-- 
tejun
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/