[sheepdog] [PATCH 1/3] sheep: queue local gateway request instead of directly call forward_*_obj_req

[levin li]

On 06/25/2012 07:21 PM, Christoph Hellwig wrote:
> On Mon, Jun 25, 2012 at 07:17:07PM +0800, Liu Yuan wrote:
>> On 06/25/2012 07:10 PM, Christoph Hellwig wrote:
>>> How do you ensure this is always called from the main thread?  Calling
>>> queue_request from helper threads seems like it would cause major
>>> problems.
>>
>> What kind of problems?
>>
>> For now queue_request() is already called in worker threads context.
>> Looks to me we should add a thread safe version of queue_request() that
>> can be called in worker threads.
> 
>  - get_vnode_info is expected to be called from the main thread,
>  - req_done is expected to be called freom the main thread
>  - and most serious one is request_in_recovery, which manipulates
>    sys->wait_rw_queue and sys->wait_obj_queue without taking locks.
> 

Ah, it's really a problem to call queue_request() from worker thread, and
now exec_local_req() is always called from worker thread.

Sending a gateway request through network as my previous patch does seems
the simplest way to avoid this problem, but a connection to local node is
unnecessary.

How about this, we put the work into a worker thread using queue_work()
and make queue_request() called in the worker_done() function.

thanks,

levin