Re: [PATCH v2] printk: Add console owner and waiter logic to load balance console writes

[Steven Rostedt]

On Thu, 2 Nov 2017 13:06:05 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> +		raw_spin_lock(&console_owner_lock);
> +		waiter = console_waiter;
> +		console_owner = NULL;
> +		raw_spin_unlock(&console_owner_lock);
> +
> +		/*
> +		 * If there is a waiter waiting for us, then pass the
> +		 * rest of the work load over to that waiter.
> +		 */
> +		if (waiter)
> +			break;
> +

Hmm, do I need a READ_ONCE() here?

Can gcc do the load of console_waiter outside the spin lock where 
if (waiter) is done?

Although it doesn't really matter, but it just makes the code more
fragile if it can. Should this be:

		raw_spin_lock(&console_owner_lock);
		waiter = READ_ONCE(console_waiter);
		console_owner = NULL;
		raw_spin_unlock(&console_owner_lock);

		/*
		 * If there is a waiter waiting for us, then pass the
		 * rest of the work load over to that waiter.
		 */
		if (waiter)
			break;

 ?

-- Steve