NFS refactor nfs_find_client and reference client across callback processing

Fixes a bug where the nfs_client could be freed during callback processing.
Refactor nfs_find_client to use minorversion specific means to locate the
correct nfs_client structure.

In the NFS layer, V4.0 clients are found using the callback_ident field in the
CB_COMPOUND header.  V4.1 clients are found using the sessionID in the
CB_SEQUENCE operation which is also compared against the sessionID associated
with the back channel thread after a successful CREATE_SESSION.

Each of these methods finds the one an only nfs_client associated
with the incoming callback request - so nfs_find_client_next is not needed.

In the RPC layer, the pg_authenticate call needs to find the nfs_client. For
the v4.0 callback service, the callback identifier has not been decoded so a
search by address, version, and minorversion is used.  The sessionid for the
sessions based callback service has (usually) not been set for the
pg_authenticate on a CB_NULL call which can be sent prior to the return
of a CREATE_SESSION call, so the sessionid associated with the back channel
thread is not used to find the client in pg_authenticate for CB_NULL calls.

Pass the referenced nfs_client to each CB_COMPOUND operation being proceesed
via the new cb_process_state structure. The reference is held across
cb_compound processing.

Use the new cb_process_state struct to move the NFS4ERR_RETRY_UNCACHED_REP
processing from process_op into nfs4_callback_sequence where it belongs.

Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

7 files changed, 258 insertions, 188 deletions

diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index c0b05497972b..15677e7bede5 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -16,9 +16,7 @@
 #include <linux/freezer.h>
 #include <linux/kthread.h>
 #include <linux/sunrpc/svcauth_gss.h>
-#if defined(CONFIG_NFS_V4_1)
 #include <linux/sunrpc/bc_xprt.h>
-#endif
 
 #include <net/inet_sock.h>
 
@@ -384,6 +382,23 @@ static int check_gss_callback_principal(struct nfs_client *clp,
 	return SVC_OK;
 }
 
+/* pg_authenticate method helper */
+static struct nfs_client *nfs_cb_find_client(struct svc_rqst *rqstp)
+{
+	struct nfs4_sessionid *sessionid = bc_xprt_sid(rqstp);
+	int is_cb_compound = rqstp->rq_proc == CB_COMPOUND ? 1 : 0;
+
+	dprintk("--> %s rq_proc %d\n", __func__, rqstp->rq_proc);
+	if (svc_is_backchannel(rqstp))
+		/* Sessionid (usually) set after CB_NULL ping */
+		return nfs4_find_client_sessionid(svc_addr(rqstp), sessionid,
+						  is_cb_compound);
+	else
+		/* No callback identifier in pg_authenticate */
+		return nfs4_find_client_no_ident(svc_addr(rqstp));
+}
+
+/* pg_authenticate method for nfsv4 callback threads. */
 static int nfs_callback_authenticate(struct svc_rqst *rqstp)
 {
 	struct nfs_client *clp;
@@ -391,7 +406,7 @@ static int nfs_callback_authenticate(struct svc_rqst *rqstp)
 	int ret = SVC_OK;
 
 	/* Don't talk to strangers */
-	clp = nfs_find_client(svc_addr(rqstp), 4);
+	clp = nfs_cb_find_client(rqstp);
 	if (clp == NULL)
 		return SVC_DROP;
 
diff --git a/fs/nfs/callback.h b/fs/nfs/callback.h
index 58d61a8ce8b9..25e8802a51d1 100644
--- a/fs/nfs/callback.h
+++ b/fs/nfs/callback.h
@@ -34,10 +34,17 @@ enum nfs4_callback_opnum {
 	OP_CB_ILLEGAL = 10044,
 };
 
+struct cb_process_state {
+	__be32			drc_status;
+	struct nfs_client	*clp;
+	struct nfs4_sessionid	*svc_sid; /* v4.1 callback service sessionid */
+};
+
 struct cb_compound_hdr_arg {
 	unsigned int taglen;
 	const char *tag;
 	unsigned int minorversion;
+	unsigned int cb_ident; /* v4.0 callback identifier */
 	unsigned nops;
 };
 
@@ -103,8 +110,9 @@ struct cb_sequenceres {
 	uint32_t			csr_target_highestslotid;
 };
 
-extern unsigned nfs4_callback_sequence(struct cb_sequenceargs *args,
-				       struct cb_sequenceres *res);
+extern __be32 nfs4_callback_sequence(struct cb_sequenceargs *args,
+				       struct cb_sequenceres *res,
+				       struct cb_process_state *cps);
 
 extern int nfs41_validate_delegation_stateid(struct nfs_delegation *delegation,
 					     const nfs4_stateid *stateid);
@@ -118,19 +126,25 @@ struct cb_recallanyargs {
 	uint32_t	craa_type_mask;
 };
 
-extern unsigned nfs4_callback_recallany(struct cb_recallanyargs *args, void *dummy);
+extern __be32 nfs4_callback_recallany(struct cb_recallanyargs *args,
+					void *dummy,
+					struct cb_process_state *cps);
 
 struct cb_recallslotargs {
 	struct sockaddr	*crsa_addr;
 	uint32_t	crsa_target_max_slots;
 };
-extern unsigned nfs4_callback_recallslot(struct cb_recallslotargs *args,
-					  void *dummy);
+extern __be32 nfs4_callback_recallslot(struct cb_recallslotargs *args,
+					 void *dummy,
+					 struct cb_process_state *cps);
 
 #endif /* CONFIG_NFS_V4_1 */
 
-extern __be32 nfs4_callback_getattr(struct cb_getattrargs *args, struct cb_getattrres *res);
-extern __be32 nfs4_callback_recall(struct cb_recallargs *args, void *dummy);
+extern __be32 nfs4_callback_getattr(struct cb_getattrargs *args,
+				    struct cb_getattrres *res,
+				    struct cb_process_state *cps);
+extern __be32 nfs4_callback_recall(struct cb_recallargs *args, void *dummy,
+				   struct cb_process_state *cps);
 
 #ifdef CONFIG_NFS_V4
 extern int nfs_callback_up(u32 minorversion, struct rpc_xprt *xprt);
diff --git a/fs/nfs/callback_proc.c b/fs/nfs/callback_proc.c
index 2950fca0c61b..b70e46da16fc 100644
--- a/fs/nfs/callback_proc.c
+++ b/fs/nfs/callback_proc.c
@@ -16,26 +16,28 @@
 #ifdef NFS_DEBUG
 #define NFSDBG_FACILITY NFSDBG_CALLBACK
 #endif
- 
-__be32 nfs4_callback_getattr(struct cb_getattrargs *args, struct cb_getattrres *res)
+
+__be32 nfs4_callback_getattr(struct cb_getattrargs *args,
+			     struct cb_getattrres *res,
+			     struct cb_process_state *cps)
 {
-	struct nfs_client *clp;
 	struct nfs_delegation *delegation;
 	struct nfs_inode *nfsi;
 	struct inode *inode;
 
+	res->status = htonl(NFS4ERR_OP_NOT_IN_SESSION);
+	if (!cps->clp) /* Always set for v4.0. Set in cb_sequence for v4.1 */
+		goto out;
+
 	res->bitmap[0] = res->bitmap[1] = 0;
 	res->status = htonl(NFS4ERR_BADHANDLE);
-	clp = nfs_find_client(args->addr, 4);
-	if (clp == NULL)
-		goto out;
 
 	dprintk("NFS: GETATTR callback request from %s\n",
-		rpc_peeraddr2str(clp->cl_rpcclient, RPC_DISPLAY_ADDR));
+		rpc_peeraddr2str(cps->clp->cl_rpcclient, RPC_DISPLAY_ADDR));
 
-	inode = nfs_delegation_find_inode(clp, &args->fh);
+	inode = nfs_delegation_find_inode(cps->clp, &args->fh);
 	if (inode == NULL)
-		goto out_putclient;
+		goto out;
 	nfsi = NFS_I(inode);
 	rcu_read_lock();
 	delegation = rcu_dereference(nfsi->delegation);
@@ -55,49 +57,41 @@ __be32 nfs4_callback_getattr(struct cb_getattrargs *args, struct cb_getattrres *
 out_iput:
 	rcu_read_unlock();
 	iput(inode);
-out_putclient:
-	nfs_put_client(clp);
 out:
 	dprintk("%s: exit with status = %d\n", __func__, ntohl(res->status));
 	return res->status;
 }
 
-__be32 nfs4_callback_recall(struct cb_recallargs *args, void *dummy)
+__be32 nfs4_callback_recall(struct cb_recallargs *args, void *dummy,
+			    struct cb_process_state *cps)
 {
-	struct nfs_client *clp;
 	struct inode *inode;
 	__be32 res;
 	
-	res = htonl(NFS4ERR_BADHANDLE);
-	clp = nfs_find_client(args->addr, 4);
-	if (clp == NULL)
+	res = htonl(NFS4ERR_OP_NOT_IN_SESSION);
+	if (!cps->clp) /* Always set for v4.0. Set in cb_sequence for v4.1 */
 		goto out;
 
 	dprintk("NFS: RECALL callback request from %s\n",
-		rpc_peeraddr2str(clp->cl_rpcclient, RPC_DISPLAY_ADDR));
-
-	do {
-		struct nfs_client *prev = clp;
-
-		inode = nfs_delegation_find_inode(clp, &args->fh);
-		if (inode != NULL) {
-			/* Set up a helper thread to actually return the delegation */
-			switch (nfs_async_inode_return_delegation(inode, &args->stateid)) {
-				case 0:
-					res = 0;
-					break;
-				case -ENOENT:
-					if (res != 0)
-						res = htonl(NFS4ERR_BAD_STATEID);
-					break;
-				default:
-					res = htonl(NFS4ERR_RESOURCE);
-			}
-			iput(inode);
-		}
-		clp = nfs_find_client_next(prev);
-		nfs_put_client(prev);
-	} while (clp != NULL);
+		rpc_peeraddr2str(cps->clp->cl_rpcclient, RPC_DISPLAY_ADDR));
+
+	res = htonl(NFS4ERR_BADHANDLE);
+	inode = nfs_delegation_find_inode(cps->clp, &args->fh);
+	if (inode == NULL)
+		goto out;
+	/* Set up a helper thread to actually return the delegation */
+	switch (nfs_async_inode_return_delegation(inode, &args->stateid)) {
+	case 0:
+		res = 0;
+		break;
+	case -ENOENT:
+		if (res != 0)
+			res = htonl(NFS4ERR_BAD_STATEID);
+		break;
+	default:
+		res = htonl(NFS4ERR_RESOURCE);
+	}
+	iput(inode);
 out:
 	dprintk("%s: exit with status = %d\n", __func__, ntohl(res));
 	return res;
@@ -185,42 +179,6 @@ validate_seqid(struct nfs4_slot_table *tbl, struct cb_sequenceargs * args)
 }
 
 /*
- * Returns a pointer to a held 'struct nfs_client' that matches the server's
- * address, major version number, and session ID.  It is the caller's
- * responsibility to release the returned reference.
- *
- * Returns NULL if there are no connections with sessions, or if no session
- * matches the one of interest.
- */
- static struct nfs_client *find_client_with_session(
-	const struct sockaddr *addr, u32 nfsversion,
-	struct nfs4_sessionid *sessionid)
-{
-	struct nfs_client *clp;
-
-	clp = nfs_find_client(addr, 4);
-	if (clp == NULL)
-		return NULL;
-
-	do {
-		struct nfs_client *prev = clp;
-
-		if (clp->cl_session != NULL) {
-			if (memcmp(clp->cl_session->sess_id.data,
-					sessionid->data,
-					NFS4_MAX_SESSIONID_LEN) == 0) {
-				/* Returns a held reference to clp */
-				return clp;
-			}
-		}
-		clp = nfs_find_client_next(prev);
-		nfs_put_client(prev);
-	} while (clp != NULL);
-
-	return NULL;
-}
-
-/*
  * For each referring call triple, check the session's slot table for
  * a match.  If the slot is in use and the sequence numbers match, the
  * client is still waiting for a response to the original request.
@@ -276,20 +234,28 @@ out:
 }
 
 __be32 nfs4_callback_sequence(struct cb_sequenceargs *args,
-				struct cb_sequenceres *res)
+			      struct cb_sequenceres *res,
+			      struct cb_process_state *cps)
 {
 	struct nfs_client *clp;
 	int i;
 	__be32 status;
 
+	cps->clp = NULL;
+
 	status = htonl(NFS4ERR_BADSESSION);
-	clp = find_client_with_session(args->csa_addr, 4, &args->csa_sessionid);
+	/* Incoming session must match the callback session */
+	if (memcmp(&args->csa_sessionid, cps->svc_sid, NFS4_MAX_SESSIONID_LEN))
+		goto out;
+
+	clp = nfs4_find_client_sessionid(args->csa_addr,
+					 &args->csa_sessionid, 1);
 	if (clp == NULL)
 		goto out;
 
 	status = validate_seqid(&clp->cl_session->bc_slot_table, args);
 	if (status)
-		goto out_putclient;
+		goto out;
 
 	/*
 	 * Check for pending referring calls.  If a match is found, a
@@ -298,7 +264,7 @@ __be32 nfs4_callback_sequence(struct cb_sequenceargs *args,
 	 */
 	if (referring_call_exists(clp, args->csa_nrclists, args->csa_rclists)) {
 		status = htonl(NFS4ERR_DELAY);
-		goto out_putclient;
+		goto out;
 	}
 
 	memcpy(&res->csr_sessionid, &args->csa_sessionid,
@@ -307,36 +273,36 @@ __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;
+	cps->clp = clp; /* put in nfs4_callback_compound */
 
-out_putclient:
-	nfs_put_client(clp);
 out:
 	for (i = 0; i < args->csa_nrclists; i++)
 		kfree(args->csa_rclists[i].rcl_refcalls);
 	kfree(args->csa_rclists);
 
-	if (status == htonl(NFS4ERR_RETRY_UNCACHED_REP))
-		res->csr_status = 0;
-	else
+	if (status == htonl(NFS4ERR_RETRY_UNCACHED_REP)) {
+		cps->drc_status = status;
+		status = 0;
+	} else
 		res->csr_status = status;
+
 	dprintk("%s: exit with status = %d res->csr_status %d\n", __func__,
 		ntohl(status), ntohl(res->csr_status));
 	return status;
 }
 
-__be32 nfs4_callback_recallany(struct cb_recallanyargs *args, void *dummy)
+__be32 nfs4_callback_recallany(struct cb_recallanyargs *args, void *dummy,
+			       struct cb_process_state *cps)
 {
-	struct nfs_client *clp;
 	__be32 status;
 	fmode_t flags = 0;
 
 	status = htonl(NFS4ERR_OP_NOT_IN_SESSION);
-	clp = nfs_find_client(args->craa_addr, 4);
-	if (clp == NULL)
+	if (!cps->clp) /* set in cb_sequence */
 		goto out;
 
 	dprintk("NFS: RECALL_ANY callback request from %s\n",
-		rpc_peeraddr2str(clp->cl_rpcclient, RPC_DISPLAY_ADDR));
+		rpc_peeraddr2str(cps->clp->cl_rpcclient, RPC_DISPLAY_ADDR));
 
 	if (test_bit(RCA4_TYPE_MASK_RDATA_DLG, (const unsigned long *)
 		     &args->craa_type_mask))
@@ -346,7 +312,7 @@ __be32 nfs4_callback_recallany(struct cb_recallanyargs *args, void *dummy)
 		flags |= FMODE_WRITE;
 
 	if (flags)
-		nfs_expire_all_delegation_types(clp, flags);
+		nfs_expire_all_delegation_types(cps->clp, flags);
 	status = htonl(NFS4_OK);
 out:
 	dprintk("%s: exit with status = %d\n", __func__, ntohl(status));
@@ -354,36 +320,33 @@ out:
 }
 
 /* Reduce the fore channel's max_slots to the target value */
-__be32 nfs4_callback_recallslot(struct cb_recallslotargs *args, void *dummy)
+__be32 nfs4_callback_recallslot(struct cb_recallslotargs *args, void *dummy,
+				struct cb_process_state *cps)
 {
-	struct nfs_client *clp;
 	struct nfs4_slot_table *fc_tbl;
 	__be32 status;
 
 	status = htonl(NFS4ERR_OP_NOT_IN_SESSION);
-	clp = nfs_find_client(args->crsa_addr, 4);
-	if (clp == NULL)
+	if (!cps->clp) /* set in cb_sequence */
 		goto out;
 
 	dprintk("NFS: CB_RECALL_SLOT request from %s target max slots %d\n",
-		rpc_peeraddr2str(clp->cl_rpcclient, RPC_DISPLAY_ADDR),
+		rpc_peeraddr2str(cps->clp->cl_rpcclient, RPC_DISPLAY_ADDR),
 		args->crsa_target_max_slots);
 
-	fc_tbl = &clp->cl_session->fc_slot_table;
+	fc_tbl = &cps->clp->cl_session->fc_slot_table;
 
 	status = htonl(NFS4ERR_BAD_HIGH_SLOT);
 	if (args->crsa_target_max_slots > fc_tbl->max_slots ||
 	    args->crsa_target_max_slots < 1)
-		goto out_putclient;
+		goto out;
 
 	status = htonl(NFS4_OK);
 	if (args->crsa_target_max_slots == fc_tbl->max_slots)
-		goto out_putclient;
+		goto out;
 
 	fc_tbl->target_max_slots = args->crsa_target_max_slots;
-	nfs41_handle_recall_slot(clp);
-out_putclient:
-	nfs_put_client(clp);	/* balance nfs_find_client */
+	nfs41_handle_recall_slot(cps->clp);
 out:
 	dprintk("%s: exit with status = %d\n", __func__, ntohl(status));
 	return status;
diff --git a/fs/nfs/callback_xdr.c b/fs/nfs/callback_xdr.c
index 05af212f0edf..dbd0d649805c 100644
--- a/fs/nfs/callback_xdr.c
+++ b/fs/nfs/callback_xdr.c
@@ -10,8 +10,10 @@
 #include <linux/nfs4.h>
 #include <linux/nfs_fs.h>
 #include <linux/slab.h>
+#include <linux/sunrpc/bc_xprt.h>
 #include "nfs4_fs.h"
 #include "callback.h"
+#include "internal.h"
 
 #define CB_OP_TAGLEN_MAXSZ	(512)
 #define CB_OP_HDR_RES_MAXSZ	(2 + CB_OP_TAGLEN_MAXSZ)
@@ -33,7 +35,8 @@
 /* Internal error code */
 #define NFS4ERR_RESOURCE_HDR	11050
 
-typedef __be32 (*callback_process_op_t)(void *, void *);
+typedef __be32 (*callback_process_op_t)(void *, void *,
+					struct cb_process_state *);
 typedef __be32 (*callback_decode_arg_t)(struct svc_rqst *, struct xdr_stream *, void *);
 typedef __be32 (*callback_encode_res_t)(struct svc_rqst *, struct xdr_stream *, void *);
 
@@ -160,7 +163,7 @@ static __be32 decode_compound_hdr_arg(struct xdr_stream *xdr, struct cb_compound
 	hdr->minorversion = ntohl(*p++);
 	/* Check minor version is zero or one. */
 	if (hdr->minorversion <= 1) {
-		p++;	/* skip callback_ident */
+		hdr->cb_ident = ntohl(*p++); /* ignored by v4.1 */
 	} else {
 		printk(KERN_WARNING "%s: NFSv4 server callback with "
 			"illegal minor version %u!\n",
@@ -621,7 +624,8 @@ preprocess_nfs4_op(unsigned int op_nr, struct callback_op **op)
 static __be32 process_op(uint32_t minorversion, int nop,
 		struct svc_rqst *rqstp,
 		struct xdr_stream *xdr_in, void *argp,
-		struct xdr_stream *xdr_out, void *resp, int* drc_status)
+		struct xdr_stream *xdr_out, void *resp,
+		struct cb_process_state *cps)
 {
 	struct callback_op *op = &callback_ops[0];
 	unsigned int op_nr;
@@ -644,8 +648,8 @@ static __be32 process_op(uint32_t minorversion, int nop,
 	if (status)
 		goto encode_hdr;
 
-	if (*drc_status) {
-		status = *drc_status;
+	if (cps->drc_status) {
+		status = cps->drc_status;
 		goto encode_hdr;
 	}
 
@@ -653,16 +657,10 @@ static __be32 process_op(uint32_t minorversion, int nop,
 	if (maxlen > 0 && maxlen < PAGE_SIZE) {
 		status = op->decode_args(rqstp, xdr_in, argp);
 		if (likely(status == 0))
-			status = op->process_op(argp, resp);
+			status = op->process_op(argp, resp, cps);
 	} else
 		status = htonl(NFS4ERR_RESOURCE);
 
-	/* Only set by OP_CB_SEQUENCE processing */
-	if (status == htonl(NFS4ERR_RETRY_UNCACHED_REP)) {
-		*drc_status = status;
-		status = 0;
-	}
-
 encode_hdr:
 	res = encode_op_hdr(xdr_out, op_nr, status);
 	if (unlikely(res))
@@ -681,8 +679,11 @@ static __be32 nfs4_callback_compound(struct svc_rqst *rqstp, void *argp, void *r
 	struct cb_compound_hdr_arg hdr_arg = { 0 };
 	struct cb_compound_hdr_res hdr_res = { NULL };
 	struct xdr_stream xdr_in, xdr_out;
-	__be32 *p;
-	__be32 status, drc_status = 0;
+	__be32 *p, status;
+	struct cb_process_state cps = {
+		.drc_status = 0,
+		.clp = NULL,
+	};
 	unsigned int nops = 0;
 
 	dprintk("%s: start\n", __func__);
@@ -696,6 +697,13 @@ static __be32 nfs4_callback_compound(struct svc_rqst *rqstp, void *argp, void *r
 	if (status == __constant_htonl(NFS4ERR_RESOURCE))
 		return rpc_garbage_args;
 
+	if (hdr_arg.minorversion == 0) {
+		cps.clp = nfs4_find_client_ident(hdr_arg.cb_ident);
+		if (!cps.clp)
+			return rpc_drop_reply;
+	} else
+		cps.svc_sid = bc_xprt_sid(rqstp);
+
 	hdr_res.taglen = hdr_arg.taglen;
 	hdr_res.tag = hdr_arg.tag;
 	if (encode_compound_hdr_res(&xdr_out, &hdr_res) != 0)
@@ -703,7 +711,7 @@ static __be32 nfs4_callback_compound(struct svc_rqst *rqstp, void *argp, void *r
 
 	while (status == 0 && nops != hdr_arg.nops) {
 		status = process_op(hdr_arg.minorversion, nops, rqstp,
-				    &xdr_in, argp, &xdr_out, resp, &drc_status);
+				    &xdr_in, argp, &xdr_out, resp, &cps);
 		nops++;
 	}
 
@@ -716,6 +724,7 @@ static __be32 nfs4_callback_compound(struct svc_rqst *rqstp, void *argp, void *r
 
 	*hdr_res.status = status;
 	*hdr_res.nops = htonl(nops);
+	nfs_put_client(cps.clp);
 	dprintk("%s: done, status = %u\n", __func__, ntohl(status));
 	return rpc_success;
 }
diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index bc3a8620e8c3..11eb9934c747 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -410,70 +410,28 @@ static int nfs_sockaddr_cmp(const struct sockaddr *sa1,
 	return 0;
 }
 
-/*
- * Find a client by IP address and protocol version
- * - returns NULL if no such client
- */
-struct nfs_client *nfs_find_client(const struct sockaddr *addr, u32 nfsversion)
+/* Common match routine for v4.0 and v4.1 callback services */
+bool
+nfs4_cb_match_client(const struct sockaddr *addr, struct nfs_client *clp,
+		     u32 minorversion)
 {
-	struct nfs_client *clp;
+	struct sockaddr *clap = (struct sockaddr *)&clp->cl_addr;
 
-	spin_lock(&nfs_client_lock);
-	list_for_each_entry(clp, &nfs_client_list, cl_share_link) {
-		struct sockaddr *clap = (struct sockaddr *)&clp->cl_addr;
+	/* Don't match clients that failed to initialise */
+	if (!(clp->cl_cons_state == NFS_CS_READY ||
+	    clp->cl_cons_state == NFS_CS_SESSION_INITING))
+		return false;
 
-		/* Don't match clients that failed to initialise properly */
-		if (!(clp->cl_cons_state == NFS_CS_READY ||
-		      clp->cl_cons_state == NFS_CS_SESSION_INITING))
-			continue;
+	/* Match the version and minorversion */
+	if (clp->rpc_ops->version != 4 ||
+	    clp->cl_minorversion != minorversion)
+		return false;
 
-		/* Different NFS versions cannot share the same nfs_client */
-		if (clp->rpc_ops->version != nfsversion)
-			continue;
-
-		/* Match only the IP address, not the port number */
-		if (!nfs_sockaddr_match_ipaddr(addr, clap))
-			continue;
+	/* Match only the IP address, not the port number */
+	if (!nfs_sockaddr_match_ipaddr(addr, clap))
+		return false;
 
-		atomic_inc(&clp->cl_count);
-		spin_unlock(&nfs_client_lock);
-		return clp;
-	}
-	spin_unlock(&nfs_client_lock);
-	return NULL;
-}
-
-/*
- * Find a client by IP address and protocol version
- * - returns NULL if no such client
- */
-struct nfs_client *nfs_find_client_next(struct nfs_client *clp)
-{
-	struct sockaddr *sap = (struct sockaddr *)&clp->cl_addr;
-	u32 nfsvers = clp->rpc_ops->version;
-
-	spin_lock(&nfs_client_lock);
-	list_for_each_entry_continue(clp, &nfs_client_list, cl_share_link) {
-		struct sockaddr *clap = (struct sockaddr *)&clp->cl_addr;
-
-		/* Don't match clients that failed to initialise properly */
-		if (clp->cl_cons_state != NFS_CS_READY)
-			continue;
-
-		/* Different NFS versions cannot share the same nfs_client */
-		if (clp->rpc_ops->version != nfsvers)
-			continue;
-
-		/* Match only the IP address, not the port number */
-		if (!nfs_sockaddr_match_ipaddr(sap, clap))
-			continue;
-
-		atomic_inc(&clp->cl_count);
-		spin_unlock(&nfs_client_lock);
-		return clp;
-	}
-	spin_unlock(&nfs_client_lock);
-	return NULL;
+	return true;
 }
 
 /*
@@ -1172,6 +1130,101 @@ error:
 
 #ifdef CONFIG_NFS_V4
 /*
+ * NFSv4.0 callback thread helper
+ *
+ * Find a client by IP address, protocol version, and minorversion
+ *
+ * Called from the pg_authenticate method. The callback identifier
+ * is not used as it has not been decoded.
+ *
+ * Returns NULL if no such client
+ */
+struct nfs_client *
+nfs4_find_client_no_ident(const struct sockaddr *addr)
+{
+	struct nfs_client *clp;
+
+	spin_lock(&nfs_client_lock);
+	list_for_each_entry(clp, &nfs_client_list, cl_share_link) {
+		if (nfs4_cb_match_client(addr, clp, 0) == false)
+			continue;
+		atomic_inc(&clp->cl_count);
+		spin_unlock(&nfs_client_lock);
+		return clp;
+	}
+	spin_unlock(&nfs_client_lock);
+	return NULL;
+}
+
+/*
+ * NFSv4.0 callback thread helper
+ *
+ * Find a client by callback identifier
+ */
+struct nfs_client *
+nfs4_find_client_ident(int cb_ident)
+{
+	struct nfs_client *clp;
+
+	spin_lock(&nfs_client_lock);
+	clp = idr_find(&cb_ident_idr, cb_ident);
+	if (clp)
+		atomic_inc(&clp->cl_count);
+	spin_unlock(&nfs_client_lock);
+	return clp;
+}
+
+#if defined(CONFIG_NFS_V4_1)
+/*
+ * NFSv4.1 callback thread helper
+ * For CB_COMPOUND calls, find a client by IP address, protocol version,
+ * minorversion, and sessionID
+ *
+ * CREATE_SESSION triggers a CB_NULL ping from servers. The callback service
+ * sessionid can only be set after the CREATE_SESSION return, so a CB_NULL
+ * can arrive before the callback sessionid is set. For CB_NULL calls,
+ * find a client by IP address protocol version, and minorversion.
+ *
+ * Returns NULL if no such client
+ */
+struct nfs_client *
+nfs4_find_client_sessionid(const struct sockaddr *addr,
+			   struct nfs4_sessionid *sid, int is_cb_compound)
+{
+	struct nfs_client *clp;
+
+	spin_lock(&nfs_client_lock);
+	list_for_each_entry(clp, &nfs_client_list, cl_share_link) {
+		if (nfs4_cb_match_client(addr, clp, 1) == false)
+			continue;
+
+		if (!nfs4_has_session(clp))
+			continue;
+
+		/* Match sessionid unless cb_null call*/
+		if (is_cb_compound && (memcmp(clp->cl_session->sess_id.data,
+		    sid->data, NFS4_MAX_SESSIONID_LEN) != 0))
+			continue;
+
+		atomic_inc(&clp->cl_count);
+		spin_unlock(&nfs_client_lock);
+		return clp;
+	}
+	spin_unlock(&nfs_client_lock);
+	return NULL;
+}
+
+#else /* CONFIG_NFS_V4_1 */
+
+struct nfs_client *
+nfs4_find_client_sessionid(const struct sockaddr *addr,
+			   struct nfs4_sessionid *sid, int is_cb_compound)
+{
+	return NULL;
+}
+#endif /* CONFIG_NFS_V4_1 */
+
+/*
  * Initialize the NFS4 callback service
  */
 static int nfs4_init_callback(struct nfs_client *clp)
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index 7c803c916574..bfa3a34af801 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -130,8 +130,11 @@ extern struct rpc_program nfs_program;
 
 extern void nfs_cleanup_cb_ident_idr(void);
 extern void nfs_put_client(struct nfs_client *);
-extern struct nfs_client *nfs_find_client(const struct sockaddr *, u32);
-extern struct nfs_client *nfs_find_client_next(struct nfs_client *);
+extern struct nfs_client *nfs4_find_client_no_ident(const struct sockaddr *);
+extern struct nfs_client *nfs4_find_client_ident(int);
+extern struct nfs_client *
+nfs4_find_client_sessionid(const struct sockaddr *, struct nfs4_sessionid *,
+			   int);
 extern struct nfs_server *nfs_create_server(
 					const struct nfs_parsed_mount_data *,
 					struct nfs_fh *);
diff --git a/include/linux/sunrpc/bc_xprt.h b/include/linux/sunrpc/bc_xprt.h
index 7c91260c44a9..2c60e094fdec 100644
--- a/include/linux/sunrpc/bc_xprt.h
+++ b/include/linux/sunrpc/bc_xprt.h
@@ -47,6 +47,14 @@ static inline int svc_is_backchannel(const struct svc_rqst *rqstp)
 		return 1;
 	return 0;
 }
+static inline struct nfs4_sessionid *bc_xprt_sid(struct svc_rqst *rqstp)
+{
+	if (svc_is_backchannel(rqstp))
+		return (struct nfs4_sessionid *)
+					rqstp->rq_server->bc_xprt->xpt_bc_sid;
+	return NULL;
+}
+
 #else /* CONFIG_NFS_V4_1 */
 static inline int xprt_setup_backchannel(struct rpc_xprt *xprt,
 					 unsigned int min_reqs)
@@ -59,6 +67,11 @@ static inline int svc_is_backchannel(const struct svc_rqst *rqstp)
 	return 0;
 }
 
+static inline struct nfs4_sessionid *bc_xprt_sid(struct svc_rqst *rqstp)
+{
+	return NULL;
+}
+
 static inline void xprt_free_bc_request(struct rpc_rqst *req)
 {
 }