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From:   schumaker.anna@gmail.com
To:     linux-nfs@vger.kernel.org
Cc:     Anna.Schumaker@Netapp.com
Subject: [PATCH v1 1/1] NFS: Fix interrupted slots by sending a solo SEQUENCE operation
Date:   Wed,  8 Jul 2020 11:50:18 -0400
Message-Id: <20200708155018.110150-2-Anna.Schumaker@Netapp.com>
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From: Anna Schumaker <Anna.Schumaker@Netapp.com>

We used to do this before 3453d5708b33, but this was changed to better
handle the NFS4ERR_SEQ_MISORDERED error code. This commit fixed the slot
re-use case when the server doesn't receive the interrupted operation,
but if the server does receive the operation then it could still end up
replying to the client with mis-matched operations from the reply cache.

We can fix this by sending a SEQUENCE to the server while recovering from
a SEQ_MISORDERED error when we detect that we are in an interrupted slot
situation.

Fixes: 3453d5708b33 (NFSv4.1: Avoid false retries when RPC calls are interrupted)
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
---
 fs/nfs/nfs4proc.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index e32717fd1169..5de41a5772f0 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -774,6 +774,14 @@ static void nfs4_slot_sequence_acked(struct nfs4_slot *slot,
 	slot->seq_nr_last_acked = seqnr;
 }
 
+static void nfs4_probe_sequence(struct nfs_client *client, const struct cred *cred,
+				struct nfs4_slot *slot)
+{
+	struct rpc_task *task = _nfs41_proc_sequence(client, cred, slot, true);
+	if (!IS_ERR(task))
+		rpc_wait_for_completion_task(task);
+}
+
 static int nfs41_sequence_process(struct rpc_task *task,
 		struct nfs4_sequence_res *res)
 {
@@ -790,6 +798,7 @@ static int nfs41_sequence_process(struct rpc_task *task,
 		goto out;
 
 	session = slot->table->session;
+	clp = session->clp;
 
 	trace_nfs4_sequence_done(session, res);
 
@@ -804,7 +813,6 @@ static int nfs41_sequence_process(struct rpc_task *task,
 		nfs4_slot_sequence_acked(slot, slot->seq_nr);
 		/* Update the slot's sequence and clientid lease timer */
 		slot->seq_done = 1;
-		clp = session->clp;
 		do_renew_lease(clp, res->sr_timestamp);
 		/* Check sequence flags */
 		nfs41_handle_sequence_flag_errors(clp, res->sr_status_flags,
@@ -852,10 +860,15 @@ static int nfs41_sequence_process(struct rpc_task *task,
 		/*
 		 * Were one or more calls using this slot interrupted?
 		 * If the server never received the request, then our
-		 * transmitted slot sequence number may be too high.
+		 * transmitted slot sequence number may be too high. However,
+		 * if the server did receive the request then it might
+		 * accidentally give us a reply with a mismatched operation.
+		 * We can sort this out by sending a lone sequence operation
+		 * to the server on the same slot.
 		 */
 		if ((s32)(slot->seq_nr - slot->seq_nr_last_acked) > 1) {
 			slot->seq_nr--;
+			nfs4_probe_sequence(clp, task->tk_msg.rpc_cred, slot);
 			goto retry_nowait;
 		}
 		/*
-- 
2.27.0