Re: [PATCH v2 3/3] kernel/watch_queue: Remove wqueue->defunct and use pipe for clear check

[Eric Biggers]

On Thu, Aug 04, 2022 at 08:11:52PM +0530, Siddh Raman Pant wrote:
>  static inline bool lock_wqueue(struct watch_queue *wqueue)
>  {
>  	spin_lock_bh(&wqueue->lock);
> -	if (unlikely(wqueue->defunct)) {
> +	if (unlikely(!READ_ONCE(wqueue->pipe))) {
>  		spin_unlock_bh(&wqueue->lock);
>  		return false;
>  	}

Why is the READ_ONCE() needed?  Doesn't wqueue->lock protect wqueue->pipe?

> +	/* This pipe will get freed by the caller free_pipe_info().
> +	 * Removing this reference also prevents new notifications.
> +	 */

This isn't the correct block comment format; it should look like:

	/*
	 * This pipe will get freed by the caller free_pipe_info().
	 * Removing this reference also prevents new notifications.
	 */

- Eric