NFSv4.1: Fix the callback 'highest_used_slotid' behaviour

Currently, there is no guarantee that we will call nfs4_cb_take_slot() even
though nfs4_callback_compound() will consistently call
nfs4_cb_free_slot() provided the cb_process_state has set the 'clp' field.
The result is that we can trigger the BUG_ON() upon the next call to
nfs4_cb_take_slot().

This patch fixes the above problem by using the slot id that was taken in
the CB_SEQUENCE operation as a flag for whether or not we need to call
nfs4_cb_free_slot().
It also fixes an atomicity problem: we need to set tbl->highest_used_slotid
atomically with the check for NFS4_SESSION_DRAINING, otherwise we end up
racing with the various tests in nfs4_begin_drain_session().

Cc: stable@kernel.org [2.6.38+]
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 14 insertions, 6 deletions

diff --git a/fs/nfs/callback_proc.c b/fs/nfs/callback_proc.c
index 74780f9..0ab8202 100644
--- a/fs/nfs/callback_proc.c
+++ b/fs/nfs/callback_proc.c
@@ -348,7 +348,7 @@ validate_seqid(struct nfs4_slot_table *tbl, struct cb_sequenceargs * args)
 	/* Normal */
 	if (likely(args->csa_sequenceid == slot->seq_nr + 1)) {
 		slot->seq_nr++;
-		return htonl(NFS4_OK);
+		goto out_ok;
 	}
 
 	/* Replay */
@@ -367,11 +367,14 @@ validate_seqid(struct nfs4_slot_table *tbl, struct cb_sequenceargs * args)
 	/* Wraparound */
 	if (args->csa_sequenceid == 1 && (slot->seq_nr + 1) == 0) {
 		slot->seq_nr = 1;
-		return htonl(NFS4_OK);
+		goto out_ok;
 	}
 
 	/* Misordered request */
 	return htonl(NFS4ERR_SEQ_MISORDERED);
+out_ok:
+	tbl->highest_used_slotid = args->csa_slotid;
+	return htonl(NFS4_OK);
 }
 
 /*
@@ -433,26 +436,32 @@ __be32 nfs4_callback_sequence(struct cb_sequenceargs *args,
 			      struct cb_sequenceres *res,
 			      struct cb_process_state *cps)
 {
+	struct nfs4_slot_table *tbl;
 	struct nfs_client *clp;
 	int i;
 	__be32 status = htonl(NFS4ERR_BADSESSION);
 
-	cps->clp = NULL;
-
 	clp = nfs4_find_client_sessionid(args->csa_addr, &args->csa_sessionid);
 	if (clp == NULL)
 		goto out;
 
+	tbl = &clp->cl_session->bc_slot_table;
+
+	spin_lock(&tbl->slot_tbl_lock);
 	/* state manager is resetting the session */
 	if (test_bit(NFS4_SESSION_DRAINING, &clp->cl_session->session_state)) {
-		status = NFS4ERR_DELAY;
+		spin_unlock(&tbl->slot_tbl_lock);
+		status = htonl(NFS4ERR_DELAY);
 		goto out;
 	}
 
 	status = validate_seqid(&clp->cl_session->bc_slot_table, args);
+	spin_unlock(&tbl->slot_tbl_lock);
 	if (status)
 		goto out;
 
+	cps->slotid = args->csa_slotid;
+
 	/*
 	 * Check for pending referring calls.  If a match is found, a
 	 * related callback was received before the response to the original
@@ -469,7 +478,6 @@ __be32 nfs4_callback_sequence(struct cb_sequenceargs *args,
 	res->csr_slotid = args->csa_slotid;
 	res->csr_highestslotid = NFS41_BC_MAX_CALLBACKS - 1;
 	res->csr_target_highestslotid = NFS41_BC_MAX_CALLBACKS - 1;
-	nfs4_cb_take_slot(clp);
 
 out:
 	cps->clp = clp; /* put in nfs4_callback_compound */