Re: [PATCH 1/6] lib: Implement range locks

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 31 Jan 2013 22:49:49 +0100
Jan Kara <jack@suse.cz> wrote:

> Implement range locking using interval tree.
> 
> ...
>
> +void range_lock(struct range_lock_tree *tree, struct range_lock *lock)
> +{
> +	struct interval_tree_node *node;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&tree->lock, flags);
> +	node = interval_tree_iter_first(&tree->root, lock->node.start,
> +					lock->node.last);
> +	while (node) {
> +		lock->blocking_ranges++;
> +		node = interval_tree_iter_next(node, lock->node.start,
> +					       lock->node.last);
> +	}
> +	interval_tree_insert(&lock->node, &tree->root);
> +	/* Do we need to go to sleep? */
> +	while (lock->blocking_ranges) {
> +		lock->task = current;
> +		__set_current_state(TASK_UNINTERRUPTIBLE);
> +		spin_unlock_irqrestore(&tree->lock, flags);
> +		schedule();
> +		spin_lock_irqsave(&tree->lock, flags);
> +	}
> +	spin_unlock_irqrestore(&tree->lock, flags);
> +}
>
> ...
>
> +void range_unlock(struct range_lock_tree *tree, struct range_lock *lock)
> +{
> +	struct interval_tree_node *node;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&tree->lock, flags);
> +	interval_tree_remove(&lock->node, &tree->root);
> +	node = interval_tree_iter_first(&tree->root, lock->node.start,
> +					lock->node.last);
> +	while (node) {
> +		range_lock_unblock((struct range_lock *)node);
> +		node = interval_tree_iter_next(node, lock->node.start,
> +					       lock->node.last);
> +	}
> +	spin_unlock_irqrestore(&tree->lock, flags);
> +}

What are the worst-case interrupt-off durations here?

I note that the new exported functions in this patchset are
refreshingly free of documentation ;)

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