NFS: avoid infinite loop in pnfs_update_layout.

If pnfsd_update_layout() is called on a file for which recovery has
failed it will enter a tight infinite loop.

NFS_LAYOUT_INVALID_STID will be set, nfs4_select_rw_stateid() will
return -EIO, and nfs4_schedule_stateid_recovery() will do nothing, so
nfs4_client_recover_expired_lease() will not wait.  So the code will
loop indefinitely.

Break the loop by testing the validity of the open stateid at the top of
the loop.
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/pnfs.c

@@ -1999,6 +1999,14 @@ pnfs_update_layout(struct inode *ino,
 	}
 
 lookup_again:
+	if (!nfs4_valid_open_stateid(ctx->state)) {
+		trace_pnfs_update_layout(ino, pos, count,
+					 iomode, lo, lseg,
+					 PNFS_UPDATE_LAYOUT_INVALID_OPEN);
+		lseg = ERR_PTR(-EIO);
+		goto out;
+	}
+
 	lseg = ERR_PTR(nfs4_client_recover_expired_lease(clp));
 	if (IS_ERR(lseg))
 		goto out;