locks: move freeing of leases outside of i_lock

There was only one place where we still could free a file_lock while
holding the i_lock -- lease_modify. Add a new list_head argument to the
lm_change operation, pass in a private list when calling it, and fix
those callers to dispose of the list once the lock has been dropped.

Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/nfsd/nfs4state.c

@@ -3427,11 +3427,11 @@ static void nfsd_break_deleg_cb(struct file_lock *fl)
 	spin_unlock(&fp->fi_lock);
 }
 
-static
-int nfsd_change_deleg_cb(struct file_lock **onlist, int arg)
+static int
+nfsd_change_deleg_cb(struct file_lock **onlist, int arg, struct list_head *dispose)
 {
 	if (arg & F_UNLCK)
-		return lease_modify(onlist, arg);
+		return lease_modify(onlist, arg, dispose);
 	else
 		return -EAGAIN;
 }