[PATCH 6.1.y 4/7] nfsd: handle NFS4ERR_BADSLOT on CB_SEQUENCE better

[Sasha Levin <sashal@kernel.org>]

From: Jeff Layton <jlayton@kernel.org>

[ Upstream commit 999595a651a87f4285c53710b5f600d6a141f526 ]

Currently it just restarts the call, without getting a new slot.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Stable-dep-of: 01c5d5f58a5d ("nfsd: RCU-protect cl_cb_session to fix use-after-free on session teardown")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/nfsd/nfs4callback.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index d0e5f46f0f7cd..c918fd3452f31 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -1202,6 +1202,13 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback
 		rpc_delay(task, 2 * HZ);
 		return false;
 	case -NFS4ERR_BADSLOT:
+		/*
+		 * BADSLOT means that the client and server are out of sync
+		 * as to the backchannel parameters. Mark the backchannel faulty
+		 * and restart the RPC, but leak the slot so no one uses it.
+		 */
+		nfsd4_mark_cb_fault(cb->cb_clp);
+		cb->cb_held_slot = -1;
 		goto retry_nowait;
 	case -NFS4ERR_SEQ_MISORDERED:
 		if (session->se_cb_seq_nr != 1) {
-- 
2.53.0