[RFC PATCH 1/2] mtd: nand: schedule() after releasing the device

[Peter Zijlstra]

On Mon, Nov 23, 2015 at 07:09:06PM +0100, Sebastian Andrzej Siewior wrote:
>  	/* Release the controller and the chip */
>  	spin_lock(&chip->controller->lock);
>  	chip->controller->active = NULL;
>  	chip->state = FL_READY;
> +	/*
> +	 * Check if we have a waiter. If so we will schedule() right away so the
> +	 * waiter can grab the device while it is released and not after _this_
> +	 * caller gained the device (again) without leaving the CPU in between.
> +	 */
> +	if (waitqueue_active(&chip->controller->wq))
> +		do_sched = true;
>  	wake_up(&chip->controller->wq);
>  	spin_unlock(&chip->controller->lock);
> +	if (do_sched)
> +		schedule();

I've not looked at the code, but this _cannot_ be a correct fix.

schedule() can be a no-op, that is, current can be the most eligible
task to run and be selected again.

(with FIFO and this the highest prio task in the system that is a
guarantee)

I'll try and have an actual look at the problem description later.