core: Force bad-session error upon seqid=-1

Under some rare circumstances, especially when under I/O pressure, NFS
clients such as those on macOS may try to send NFS requests with an
invalid state id (seq=-1, other:ffffffffffffffffffffffff).

This usually happens after the NFS server has been restarted and lost
information about the previous client state. Unfortunately, the macOS
client does not recover from this situation and keeps making requests to
the server. This slows down both server and client to a halt.

Send a "bad session" error upon occurring a seqid of -1. This lets the
NFS client reconnect and the server establish the correct state.

Fixes: #160
Signed-off-by: Christian Kohlschütter <[email protected]>

Author: kohlschuetter

core/src/main/java/org/dcache/nfs/v4/NFSv4StateHandler.java

@@ -238,6 +238,10 @@ public NFS4Client getClient(clientid4 clientid) throws StaleClientidException {
     }
 
     public NFS4Client getClientIdByStateId(stateid4 stateId) throws ChimeraNFSException {
+        if (stateId.seqid == -1) {
+            // invalid; force reconnect
+            throw new BadSessionException();
+        }
 
         _readLock.lock();
         try {