NFSroot hangs with bad unlock balance in Linux next

[tony@atomide.com (Tony Lindgren)]

* Al Viro <viro@ZenIV.linux.org.uk> [160509 08:41]:
> On Mon, May 09, 2016 at 08:21:38AM -0700, Tony Lindgren wrote:
> 
> > Looks like with both patches applied I still also get this eventually:
> > 
> > =====================================
> > [ BUG: bad unlock balance detected! ]
> > 4.6.0-rc7-next-20160509+ #1264 Not tainted
> > -------------------------------------
> 
> Lockdep warnings are noise.  To make them STFU try the following incremental;
> I'll fold it into #work.lookups and #for-next.  Note that it will do nothing
> to hangs - those are completely unrelated and you need Eric's patch to deal
> with them.

OK yeah that helps thanks:

Tested-by: Tony Lindgren <tony@atomide.com>

> diff --git a/fs/nfs/unlink.c b/fs/nfs/unlink.c
> index d367b06..1868246 100644
> --- a/fs/nfs/unlink.c
> +++ b/fs/nfs/unlink.c
> @@ -64,7 +64,7 @@ static void nfs_async_unlink_release(void *calldata)
>  	struct dentry *dentry = data->dentry;
>  	struct super_block *sb = dentry->d_sb;
>  
> -	up_read(&NFS_I(d_inode(dentry->d_parent))->rmdir_sem);
> +	up_read_non_owner(&NFS_I(d_inode(dentry->d_parent))->rmdir_sem);
>  	d_lookup_done(dentry);
>  	nfs_free_unlinkdata(data);
>  	dput(dentry);
> @@ -117,10 +117,10 @@ static int nfs_call_unlink(struct dentry *dentry, struct nfs_unlinkdata *data)
>  	struct inode *dir = d_inode(dentry->d_parent);
>  	struct dentry *alias;
>  
> -	down_read(&NFS_I(dir)->rmdir_sem);
> +	down_read_non_owner(&NFS_I(dir)->rmdir_sem);
>  	alias = d_alloc_parallel(dentry->d_parent, &data->args.name, &data->wq);
>  	if (IS_ERR(alias)) {
> -		up_read(&NFS_I(dir)->rmdir_sem);
> +		up_read_non_owner(&NFS_I(dir)->rmdir_sem);
>  		return 0;
>  	}
>  	if (!d_in_lookup(alias)) {
> @@ -142,7 +142,7 @@ static int nfs_call_unlink(struct dentry *dentry, struct nfs_unlinkdata *data)
>  			ret = 0;
>  		spin_unlock(&alias->d_lock);
>  		dput(alias);
> -		up_read(&NFS_I(dir)->rmdir_sem);
> +		up_read_non_owner(&NFS_I(dir)->rmdir_sem);
>  		/*
>  		 * If we'd displaced old cached devname, free it.  At that
>  		 * point dentry is definitely not a root, so we won't need