Re: waitqueue lockdep annotation

[Jason Baron]

On 11/30/2017 05:11 PM, Christoph Hellwig wrote:
> On Thu, Nov 30, 2017 at 04:38:02PM -0500, Jason Baron wrote:
>> I don't think there is a bug here. The 'wake_up_locked()' calls in epoll
>> are being protected by the ep->lock, not the wait_queue_head lock. So
>> arguably the 'annotation' is wrong, but I don't think there is a bug
>> beyond that.
> 
> They can't be protected by ep->lock.  The file might as well be
> watched for using poll or select as well, or just using epoll using
> another epoll fd.
> 

Yes, but for those cases it uses the ep->poll_wait waitqueue not the
ep->wq, which is guarded by the ep->wq->lock.

See the comments in 'struct eventpoll':

        /* Wait queue used by sys_epoll_wait() */


        wait_queue_head_t wq;





        /* Wait queue used by file->poll() */


        wait_queue_head_t poll_wait;

Thanks,

-Jason