Re: [PATCH] locking/rwsem: Make rwsem_is_contended() track status of OSQ

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Mar 07, 2017 at 11:03:48AM -0500, Waiman Long wrote:
> It was found that the current rwsem_is_contended() function did not
> look at the status of the OSQ and hence would miss waiters on OSQ. So
> that function is now modified to look at the OSQ as well.

Ideally I'd kill the entire function.

	if (need_resched() ||
	    rwsem_is_contended(&fs_info->commit_root_sem)) {
		if (wakeup)
			caching_ctl->progress = last;
		btrfs_release_path(path);
		up_read(&fs_info->commit_root_sem);
		mutex_unlock(&caching_ctl->mutex);
		cond_resched();
		mutex_lock(&caching_ctl->mutex);
		down_read(&fs_info->commit_root_sem);
		goto next;
	}

is the only user of it in the entire tree and it makes no bloody sense
what so ever. rwsem is a preemptible lock after all.