Re: [PATCH 2/2] fs/epoll: deal with wait_queue only once

[Davidlohr Bueso]

On Wed, 14 Nov 2018, Andrew Morton wrote:

> Why was this moved to before the ep_reset_busy_poll_napi_id() call?
> That movement placed the code ahead of the block comment which serves
> to explain its function.

Yikes, that was a brain fart.

> This?  Which also fixes that comment and reflows it to use 80 cols.

Looks good, thanks.

> --- a/fs/eventpoll.c~fs-epoll-deal-with-wait_queue-only-once-fix
> +++ a/fs/eventpoll.c
> @@ -1787,15 +1787,6 @@ fetch_events:
> 	if (eavail)
> 		goto send_events;
>
> -	if (!waiter) {
> -		waiter = true;
> -		init_waitqueue_entry(&wait, current);
> -
> -		spin_lock_irq(&ep->wq.lock);
> -		__add_wait_queue_exclusive(&ep->wq, &wait);
> -		spin_unlock_irq(&ep->wq.lock);
> -	}
> -
> 	/*
> 	 * Busy poll timed out.  Drop NAPI ID for now, we can add
> 	 * it back in when we have moved a socket with a valid NAPI
> @@ -1804,10 +1795,18 @@ fetch_events:
> 	ep_reset_busy_poll_napi_id(ep);
>
> 	/*
> -	 * We don't have any available event to return to the caller.
> -	 * We need to sleep here, and we will be wake up by
> -	 * ep_poll_callback() when events will become available.
> +	 * We don't have any available event to return to the caller.  We need
> +	 * to sleep here, and we will be woken by ep_poll_callback() when events
> +	 * become available.
> 	 */
> +	if (!waiter) {
> +		waiter = true;
> +		init_waitqueue_entry(&wait, current);
> +
> +		spin_lock_irq(&ep->wq.lock);
> +		__add_wait_queue_exclusive(&ep->wq, &wait);
> +		spin_unlock_irq(&ep->wq.lock);
> +	}
>
> 	for (;;) {
> 		/*
> _