pNFS: Fix bugs in _pnfs_return_layout

We need to honour the NFS_LAYOUT_RETURN_REQUESTED bit regardless of
whether or not there are layout segments pending.
Furthermore, we should ensure that we leave the plh_return_segs list
empty.

This patch fixes a memory leak of the layout segments on plh_return_segs.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/pnfs.c

@@ -1145,7 +1145,7 @@ _pnfs_return_layout(struct inode *ino)
 	struct nfs_inode *nfsi = NFS_I(ino);
 	LIST_HEAD(tmp_list);
 	nfs4_stateid stateid;
-	int status = 0, empty;
+	int status = 0;
 	bool send;
 
 	dprintk("NFS: %s for inode %lu\n", __func__, ino->i_ino);
@@ -1159,7 +1159,14 @@ _pnfs_return_layout(struct inode *ino)
 	}
 	/* Reference matched in nfs4_layoutreturn_release */
 	pnfs_get_layout_hdr(lo);
-	empty = list_empty(&lo->plh_segs);
+	/* Is there an outstanding layoutreturn ? */
+	if (test_bit(NFS_LAYOUT_RETURN_LOCK, &lo->plh_flags)) {
+		spin_unlock(&ino->i_lock);
+		if (wait_on_bit(&lo->plh_flags, NFS_LAYOUT_RETURN,
+					TASK_UNINTERRUPTIBLE))
+			goto out_put_layout_hdr;
+		spin_lock(&ino->i_lock);
+	}
 	pnfs_clear_layoutcommit(ino, &tmp_list);
 	pnfs_mark_matching_lsegs_invalid(lo, &tmp_list, NULL, 0);
 
@@ -1173,7 +1180,7 @@ _pnfs_return_layout(struct inode *ino)
 	}
 
 	/* Don't send a LAYOUTRETURN if list was initially empty */
-	if (empty) {
+	if (!test_bit(NFS_LAYOUT_RETURN_REQUESTED, &lo->plh_flags)) {
 		spin_unlock(&ino->i_lock);
 		dprintk("NFS: %s no layout segments to return\n", __func__);
 		goto out_put_layout_hdr;