1 files changed, 613 insertions, 379 deletions

diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index 143da2eecd7..2c73cae9899 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -32,13 +32,18 @@
  */
 
 #include <linux/sunrpc/clnt.h>
+#include <linux/sunrpc/xprt.h>
 #include <linux/sunrpc/svc_xprt.h>
 #include <linux/slab.h>
 #include "nfsd.h"
 #include "state.h"
+#include "netns.h"
+#include "xdr4cb.h"
 
 #define NFSDDBG_FACILITY                NFSDDBG_PROC
 
+static void nfsd4_mark_cb_fault(struct nfs4_client *, int reason);
+
 #define NFSPROC4_CB_NULL 0
 #define NFSPROC4_CB_COMPOUND 1
 
@@ -50,90 +55,6 @@ enum {
 	NFSPROC4_CLNT_CB_SEQUENCE,
 };
 
-enum nfs_cb_opnum4 {
-	OP_CB_RECALL            = 4,
-	OP_CB_SEQUENCE          = 11,
-};
-
-#define NFS4_MAXTAGLEN		20
-
-#define NFS4_enc_cb_null_sz		0
-#define NFS4_dec_cb_null_sz		0
-#define cb_compound_enc_hdr_sz		4
-#define cb_compound_dec_hdr_sz		(3 + (NFS4_MAXTAGLEN >> 2))
-#define sessionid_sz			(NFS4_MAX_SESSIONID_LEN >> 2)
-#define cb_sequence_enc_sz		(sessionid_sz + 4 +             \
-					1 /* no referring calls list yet */)
-#define cb_sequence_dec_sz		(op_dec_sz + sessionid_sz + 4)
-
-#define op_enc_sz			1
-#define op_dec_sz			2
-#define enc_nfs4_fh_sz			(1 + (NFS4_FHSIZE >> 2))
-#define enc_stateid_sz			(NFS4_STATEID_SIZE >> 2)
-#define NFS4_enc_cb_recall_sz		(cb_compound_enc_hdr_sz +       \
-					cb_sequence_enc_sz +            \
-					1 + enc_stateid_sz +            \
-					enc_nfs4_fh_sz)
-
-#define NFS4_dec_cb_recall_sz		(cb_compound_dec_hdr_sz  +      \
-					cb_sequence_dec_sz +            \
-					op_dec_sz)
-
-/*
-* Generic encode routines from fs/nfs/nfs4xdr.c
-*/
-static inline __be32 *
-xdr_writemem(__be32 *p, const void *ptr, int nbytes)
-{
-	int tmp = XDR_QUADLEN(nbytes);
-	if (!tmp)
-		return p;
-	p[tmp-1] = 0;
-	memcpy(p, ptr, nbytes);
-	return p + tmp;
-}
-
-#define WRITE32(n)               *p++ = htonl(n)
-#define WRITEMEM(ptr,nbytes)     do {                           \
-	p = xdr_writemem(p, ptr, nbytes);                       \
-} while (0)
-#define RESERVE_SPACE(nbytes)   do {                            \
-	p = xdr_reserve_space(xdr, nbytes);                     \
-	if (!p) dprintk("NFSD: RESERVE_SPACE(%d) failed in function %s\n", (int) (nbytes), __func__); \
-	BUG_ON(!p);                                             \
-} while (0)
-
-/*
- * Generic decode routines from fs/nfs/nfs4xdr.c
- */
-#define DECODE_TAIL                             \
-	status = 0;                             \
-out:                                            \
-	return status;                          \
-xdr_error:                                      \
-	dprintk("NFSD: xdr error! (%s:%d)\n", __FILE__, __LINE__); \
-	status = -EIO;                          \
-	goto out
-
-#define READ32(x)         (x) = ntohl(*p++)
-#define READ64(x)         do {                  \
-	(x) = (u64)ntohl(*p++) << 32;           \
-	(x) |= ntohl(*p++);                     \
-} while (0)
-#define READTIME(x)       do {                  \
-	p++;                                    \
-	(x.tv_sec) = ntohl(*p++);               \
-	(x.tv_nsec) = ntohl(*p++);              \
-} while (0)
-#define READ_BUF(nbytes)  do { \
-	p = xdr_inline_decode(xdr, nbytes); \
-	if (!p) { \
-		dprintk("NFSD: %s: reply buffer overflowed in line %d.\n", \
-			__func__, __LINE__); \
-		return -EIO; \
-	} \
-} while (0)
-
 struct nfs4_cb_compound_hdr {
 	/* args */
 	u32		ident;	/* minorversion 0 only */
@@ -144,271 +65,489 @@ struct nfs4_cb_compound_hdr {
 	int		status;
 };
 
-static struct {
-int stat;
-int errno;
-} nfs_cb_errtbl[] = {
-	{ NFS4_OK,		0               },
-	{ NFS4ERR_PERM,		EPERM           },
-	{ NFS4ERR_NOENT,	ENOENT          },
-	{ NFS4ERR_IO,		EIO             },
-	{ NFS4ERR_NXIO,		ENXIO           },
-	{ NFS4ERR_ACCESS,	EACCES          },
-	{ NFS4ERR_EXIST,	EEXIST          },
-	{ NFS4ERR_XDEV,		EXDEV           },
-	{ NFS4ERR_NOTDIR,	ENOTDIR         },
-	{ NFS4ERR_ISDIR,	EISDIR          },
-	{ NFS4ERR_INVAL,	EINVAL          },
-	{ NFS4ERR_FBIG,		EFBIG           },
-	{ NFS4ERR_NOSPC,	ENOSPC          },
-	{ NFS4ERR_ROFS,		EROFS           },
-	{ NFS4ERR_MLINK,	EMLINK          },
-	{ NFS4ERR_NAMETOOLONG,	ENAMETOOLONG    },
-	{ NFS4ERR_NOTEMPTY,	ENOTEMPTY       },
-	{ NFS4ERR_DQUOT,	EDQUOT          },
-	{ NFS4ERR_STALE,	ESTALE          },
-	{ NFS4ERR_BADHANDLE,	EBADHANDLE      },
-	{ NFS4ERR_BAD_COOKIE,	EBADCOOKIE      },
-	{ NFS4ERR_NOTSUPP,	ENOTSUPP        },
-	{ NFS4ERR_TOOSMALL,	ETOOSMALL       },
-	{ NFS4ERR_SERVERFAULT,	ESERVERFAULT    },
-	{ NFS4ERR_BADTYPE,	EBADTYPE        },
-	{ NFS4ERR_LOCKED,	EAGAIN          },
-	{ NFS4ERR_RESOURCE,	EREMOTEIO       },
-	{ NFS4ERR_SYMLINK,	ELOOP           },
-	{ NFS4ERR_OP_ILLEGAL,	EOPNOTSUPP      },
-	{ NFS4ERR_DEADLOCK,	EDEADLK         },
-	{ -1,                   EIO             }
-};
+/*
+ * Handle decode buffer overflows out-of-line.
+ */
+static void print_overflow_msg(const char *func, const struct xdr_stream *xdr)
+{
+	dprintk("NFS: %s prematurely hit the end of our receive buffer. "
+		"Remaining buffer length is %tu words.\n",
+		func, xdr->end - xdr->p);
+}
 
-static int
-nfs_cb_stat_to_errno(int stat)
+static __be32 *xdr_encode_empty_array(__be32 *p)
 {
-	int i;
-	for (i = 0; nfs_cb_errtbl[i].stat != -1; i++) {
-		if (nfs_cb_errtbl[i].stat == stat)
-			return nfs_cb_errtbl[i].errno;
-	}
-	/* If we cannot translate the error, the recovery routines should
-	* handle it.
-	* Note: remaining NFSv4 error codes have values > 10000, so should
-	* not conflict with native Linux error codes.
-	*/
-	return stat;
+	*p++ = xdr_zero;
+	return p;
 }
 
 /*
- * XDR encode
+ * Encode/decode NFSv4 CB basic data types
+ *
+ * Basic NFSv4 callback data types are defined in section 15 of RFC
+ * 3530: "Network File System (NFS) version 4 Protocol" and section
+ * 20 of RFC 5661: "Network File System (NFS) Version 4 Minor Version
+ * 1 Protocol"
+ */
+
+/*
+ *	nfs_cb_opnum4
+ *
+ *	enum nfs_cb_opnum4 {
+ *		OP_CB_GETATTR		= 3,
+ *		  ...
+ *	};
  */
+enum nfs_cb_opnum4 {
+	OP_CB_GETATTR			= 3,
+	OP_CB_RECALL			= 4,
+	OP_CB_LAYOUTRECALL		= 5,
+	OP_CB_NOTIFY			= 6,
+	OP_CB_PUSH_DELEG		= 7,
+	OP_CB_RECALL_ANY		= 8,
+	OP_CB_RECALLABLE_OBJ_AVAIL	= 9,
+	OP_CB_RECALL_SLOT		= 10,
+	OP_CB_SEQUENCE			= 11,
+	OP_CB_WANTS_CANCELLED		= 12,
+	OP_CB_NOTIFY_LOCK		= 13,
+	OP_CB_NOTIFY_DEVICEID		= 14,
+	OP_CB_ILLEGAL			= 10044
+};
 
-static void
-encode_stateid(struct xdr_stream *xdr, stateid_t *sid)
+static void encode_nfs_cb_opnum4(struct xdr_stream *xdr, enum nfs_cb_opnum4 op)
 {
 	__be32 *p;
 
-	RESERVE_SPACE(sizeof(stateid_t));
-	WRITE32(sid->si_generation);
-	WRITEMEM(&sid->si_opaque, sizeof(stateid_opaque_t));
+	p = xdr_reserve_space(xdr, 4);
+	*p = cpu_to_be32(op);
 }
 
-static void
-encode_cb_compound_hdr(struct xdr_stream *xdr, struct nfs4_cb_compound_hdr *hdr)
+/*
+ * nfs_fh4
+ *
+ *	typedef opaque nfs_fh4<NFS4_FHSIZE>;
+ */
+static void encode_nfs_fh4(struct xdr_stream *xdr, const struct knfsd_fh *fh)
 {
-	__be32 * p;
+	u32 length = fh->fh_size;
+	__be32 *p;
 
-	RESERVE_SPACE(16);
-	WRITE32(0);            /* tag length is always 0 */
-	WRITE32(hdr->minorversion);
-	WRITE32(hdr->ident);
-	hdr->nops_p = p;
-	WRITE32(hdr->nops);
+	BUG_ON(length > NFS4_FHSIZE);
+	p = xdr_reserve_space(xdr, 4 + length);
+	xdr_encode_opaque(p, &fh->fh_base, length);
 }
 
-static void encode_cb_nops(struct nfs4_cb_compound_hdr *hdr)
+/*
+ * stateid4
+ *
+ *	struct stateid4 {
+ *		uint32_t	seqid;
+ *		opaque		other[12];
+ *	};
+ */
+static void encode_stateid4(struct xdr_stream *xdr, const stateid_t *sid)
 {
-	*hdr->nops_p = htonl(hdr->nops);
+	__be32 *p;
+
+	p = xdr_reserve_space(xdr, NFS4_STATEID_SIZE);
+	*p++ = cpu_to_be32(sid->si_generation);
+	xdr_encode_opaque_fixed(p, &sid->si_opaque, NFS4_STATEID_OTHER_SIZE);
 }
 
-static void
-encode_cb_recall(struct xdr_stream *xdr, struct nfs4_delegation *dp,
-		struct nfs4_cb_compound_hdr *hdr)
+/*
+ * sessionid4
+ *
+ *	typedef opaque sessionid4[NFS4_SESSIONID_SIZE];
+ */
+static void encode_sessionid4(struct xdr_stream *xdr,
+			      const struct nfsd4_session *session)
 {
 	__be32 *p;
-	int len = dp->dl_fh.fh_size;
-
-	RESERVE_SPACE(4);
-	WRITE32(OP_CB_RECALL);
-	encode_stateid(xdr, &dp->dl_stateid);
-	RESERVE_SPACE(8 + (XDR_QUADLEN(len) << 2));
-	WRITE32(0); /* truncate optimization not implemented */
-	WRITE32(len);
-	WRITEMEM(&dp->dl_fh.fh_base, len);
-	hdr->nops++;
+
+	p = xdr_reserve_space(xdr, NFS4_MAX_SESSIONID_LEN);
+	xdr_encode_opaque_fixed(p, session->se_sessionid.data,
+					NFS4_MAX_SESSIONID_LEN);
 }
 
-static void
-encode_cb_sequence(struct xdr_stream *xdr, struct nfsd4_callback *cb,
-		   struct nfs4_cb_compound_hdr *hdr)
-{
-	__be32 *p;
-	struct nfsd4_session *ses = cb->cb_clp->cl_cb_session;
+/*
+ * nfsstat4
+ */
+static const struct {
+	int stat;
+	int errno;
+} nfs_cb_errtbl[] = {
+	{ NFS4_OK,		0		},
+	{ NFS4ERR_PERM,		-EPERM		},
+	{ NFS4ERR_NOENT,	-ENOENT		},
+	{ NFS4ERR_IO,		-EIO		},
+	{ NFS4ERR_NXIO,		-ENXIO		},
+	{ NFS4ERR_ACCESS,	-EACCES		},
+	{ NFS4ERR_EXIST,	-EEXIST		},
+	{ NFS4ERR_XDEV,		-EXDEV		},
+	{ NFS4ERR_NOTDIR,	-ENOTDIR	},
+	{ NFS4ERR_ISDIR,	-EISDIR		},
+	{ NFS4ERR_INVAL,	-EINVAL		},
+	{ NFS4ERR_FBIG,		-EFBIG		},
+	{ NFS4ERR_NOSPC,	-ENOSPC		},
+	{ NFS4ERR_ROFS,		-EROFS		},
+	{ NFS4ERR_MLINK,	-EMLINK		},
+	{ NFS4ERR_NAMETOOLONG,	-ENAMETOOLONG	},
+	{ NFS4ERR_NOTEMPTY,	-ENOTEMPTY	},
+	{ NFS4ERR_DQUOT,	-EDQUOT		},
+	{ NFS4ERR_STALE,	-ESTALE		},
+	{ NFS4ERR_BADHANDLE,	-EBADHANDLE	},
+	{ NFS4ERR_BAD_COOKIE,	-EBADCOOKIE	},
+	{ NFS4ERR_NOTSUPP,	-ENOTSUPP	},
+	{ NFS4ERR_TOOSMALL,	-ETOOSMALL	},
+	{ NFS4ERR_SERVERFAULT,	-ESERVERFAULT	},
+	{ NFS4ERR_BADTYPE,	-EBADTYPE	},
+	{ NFS4ERR_LOCKED,	-EAGAIN		},
+	{ NFS4ERR_RESOURCE,	-EREMOTEIO	},
+	{ NFS4ERR_SYMLINK,	-ELOOP		},
+	{ NFS4ERR_OP_ILLEGAL,	-EOPNOTSUPP	},
+	{ NFS4ERR_DEADLOCK,	-EDEADLK	},
+	{ -1,			-EIO		}
+};
 
-	if (hdr->minorversion == 0)
-		return;
+/*
+ * If we cannot translate the error, the recovery routines should
+ * handle it.
+ *
+ * Note: remaining NFSv4 error codes have values > 10000, so should
+ * not conflict with native Linux error codes.
+ */
+static int nfs_cb_stat_to_errno(int status)
+{
+	int i;
 
-	RESERVE_SPACE(1 + NFS4_MAX_SESSIONID_LEN + 20);
+	for (i = 0; nfs_cb_errtbl[i].stat != -1; i++) {
+		if (nfs_cb_errtbl[i].stat == status)
+			return nfs_cb_errtbl[i].errno;
+	}
 
-	WRITE32(OP_CB_SEQUENCE);
-	WRITEMEM(ses->se_sessionid.data, NFS4_MAX_SESSIONID_LEN);
-	WRITE32(ses->se_cb_seq_nr);
-	WRITE32(0);		/* slotid, always 0 */
-	WRITE32(0);		/* highest slotid always 0 */
-	WRITE32(0);		/* cachethis always 0 */
-	WRITE32(0); /* FIXME: support referring_call_lists */
-	hdr->nops++;
+	dprintk("NFSD: Unrecognized NFS CB status value: %u\n", status);
+	return -status;
 }
 
-static int
-nfs4_xdr_enc_cb_null(struct rpc_rqst *req, __be32 *p)
+static int decode_cb_op_status(struct xdr_stream *xdr, enum nfs_opnum4 expected,
+			       enum nfsstat4 *status)
 {
-	struct xdr_stream xdrs, *xdr = &xdrs;
+	__be32 *p;
+	u32 op;
 
-	xdr_init_encode(&xdrs, &req->rq_snd_buf, p);
-        RESERVE_SPACE(0);
+	p = xdr_inline_decode(xdr, 4 + 4);
+	if (unlikely(p == NULL))
+		goto out_overflow;
+	op = be32_to_cpup(p++);
+	if (unlikely(op != expected))
+		goto out_unexpected;
+	*status = be32_to_cpup(p);
 	return 0;
+out_overflow:
+	print_overflow_msg(__func__, xdr);
+	return -EIO;
+out_unexpected:
+	dprintk("NFSD: Callback server returned operation %d but "
+		"we issued a request for %d\n", op, expected);
+	return -EIO;
+}
+
+/*
+ * CB_COMPOUND4args
+ *
+ *	struct CB_COMPOUND4args {
+ *		utf8str_cs	tag;
+ *		uint32_t	minorversion;
+ *		uint32_t	callback_ident;
+ *		nfs_cb_argop4	argarray<>;
+ *	};
+*/
+static void encode_cb_compound4args(struct xdr_stream *xdr,
+				    struct nfs4_cb_compound_hdr *hdr)
+{
+	__be32 * p;
+
+	p = xdr_reserve_space(xdr, 4 + 4 + 4 + 4);
+	p = xdr_encode_empty_array(p);		/* empty tag */
+	*p++ = cpu_to_be32(hdr->minorversion);
+	*p++ = cpu_to_be32(hdr->ident);
+
+	hdr->nops_p = p;
+	*p = cpu_to_be32(hdr->nops);		/* argarray element count */
 }
 
-static int
-nfs4_xdr_enc_cb_recall(struct rpc_rqst *req, __be32 *p,
-		struct nfsd4_callback *cb)
+/*
+ * Update argarray element count
+ */
+static void encode_cb_nops(struct nfs4_cb_compound_hdr *hdr)
 {
-	struct xdr_stream xdr;
-	struct nfs4_delegation *args = cb->cb_op;
-	struct nfs4_cb_compound_hdr hdr = {
-		.ident = cb->cb_clp->cl_cb_ident,
-		.minorversion = cb->cb_minorversion,
-	};
+	BUG_ON(hdr->nops > NFS4_MAX_BACK_CHANNEL_OPS);
+	*hdr->nops_p = cpu_to_be32(hdr->nops);
+}
 
-	xdr_init_encode(&xdr, &req->rq_snd_buf, p);
-	encode_cb_compound_hdr(&xdr, &hdr);
-	encode_cb_sequence(&xdr, cb, &hdr);
-	encode_cb_recall(&xdr, args, &hdr);
-	encode_cb_nops(&hdr);
+/*
+ * CB_COMPOUND4res
+ *
+ *	struct CB_COMPOUND4res {
+ *		nfsstat4	status;
+ *		utf8str_cs	tag;
+ *		nfs_cb_resop4	resarray<>;
+ *	};
+ */
+static int decode_cb_compound4res(struct xdr_stream *xdr,
+				  struct nfs4_cb_compound_hdr *hdr)
+{
+	u32 length;
+	__be32 *p;
+
+	p = xdr_inline_decode(xdr, 4 + 4);
+	if (unlikely(p == NULL))
+		goto out_overflow;
+	hdr->status = be32_to_cpup(p++);
+	/* Ignore the tag */
+	length = be32_to_cpup(p++);
+	p = xdr_inline_decode(xdr, length + 4);
+	if (unlikely(p == NULL))
+		goto out_overflow;
+	hdr->nops = be32_to_cpup(p);
 	return 0;
+out_overflow:
+	print_overflow_msg(__func__, xdr);
+	return -EIO;
 }
 
+/*
+ * CB_RECALL4args
+ *
+ *	struct CB_RECALL4args {
+ *		stateid4	stateid;
+ *		bool		truncate;
+ *		nfs_fh4		fh;
+ *	};
+ */
+static void encode_cb_recall4args(struct xdr_stream *xdr,
+				  const struct nfs4_delegation *dp,
+				  struct nfs4_cb_compound_hdr *hdr)
+{
+	__be32 *p;
+
+	encode_nfs_cb_opnum4(xdr, OP_CB_RECALL);
+	encode_stateid4(xdr, &dp->dl_stid.sc_stateid);
+
+	p = xdr_reserve_space(xdr, 4);
+	*p++ = xdr_zero;			/* truncate */
 
-static int
-decode_cb_compound_hdr(struct xdr_stream *xdr, struct nfs4_cb_compound_hdr *hdr){
-        __be32 *p;
-	u32 taglen;
+	encode_nfs_fh4(xdr, &dp->dl_fh);
 
-        READ_BUF(8);
-        READ32(hdr->status);
-	/* We've got no use for the tag; ignore it: */
-        READ32(taglen);
-        READ_BUF(taglen + 4);
-        p += XDR_QUADLEN(taglen);
-        READ32(hdr->nops);
-        return 0;
+	hdr->nops++;
 }
 
-static int
-decode_cb_op_hdr(struct xdr_stream *xdr, enum nfs_opnum4 expected)
+/*
+ * CB_SEQUENCE4args
+ *
+ *	struct CB_SEQUENCE4args {
+ *		sessionid4		csa_sessionid;
+ *		sequenceid4		csa_sequenceid;
+ *		slotid4			csa_slotid;
+ *		slotid4			csa_highest_slotid;
+ *		bool			csa_cachethis;
+ *		referring_call_list4	csa_referring_call_lists<>;
+ *	};
+ */
+static void encode_cb_sequence4args(struct xdr_stream *xdr,
+				    const struct nfsd4_callback *cb,
+				    struct nfs4_cb_compound_hdr *hdr)
 {
+	struct nfsd4_session *session = cb->cb_clp->cl_cb_session;
 	__be32 *p;
-	u32 op;
-	int32_t nfserr;
-
-	READ_BUF(8);
-	READ32(op);
-	if (op != expected) {
-		dprintk("NFSD: decode_cb_op_hdr: Callback server returned "
-		         " operation %d but we issued a request for %d\n",
-		         op, expected);
-		return -EIO;
-	}
-	READ32(nfserr);
-	if (nfserr != NFS_OK)
-		return -nfs_cb_stat_to_errno(nfserr);
-	return 0;
+
+	if (hdr->minorversion == 0)
+		return;
+
+	encode_nfs_cb_opnum4(xdr, OP_CB_SEQUENCE);
+	encode_sessionid4(xdr, session);
+
+	p = xdr_reserve_space(xdr, 4 + 4 + 4 + 4 + 4);
+	*p++ = cpu_to_be32(session->se_cb_seq_nr);	/* csa_sequenceid */
+	*p++ = xdr_zero;			/* csa_slotid */
+	*p++ = xdr_zero;			/* csa_highest_slotid */
+	*p++ = xdr_zero;			/* csa_cachethis */
+	xdr_encode_empty_array(p);		/* csa_referring_call_lists */
+
+	hdr->nops++;
 }
 
 /*
+ * CB_SEQUENCE4resok
+ *
+ *	struct CB_SEQUENCE4resok {
+ *		sessionid4	csr_sessionid;
+ *		sequenceid4	csr_sequenceid;
+ *		slotid4		csr_slotid;
+ *		slotid4		csr_highest_slotid;
+ *		slotid4		csr_target_highest_slotid;
+ *	};
+ *
+ *	union CB_SEQUENCE4res switch (nfsstat4 csr_status) {
+ *	case NFS4_OK:
+ *		CB_SEQUENCE4resok	csr_resok4;
+ *	default:
+ *		void;
+ *	};
+ *
  * Our current back channel implmentation supports a single backchannel
  * with a single slot.
  */
-static int
-decode_cb_sequence(struct xdr_stream *xdr, struct nfsd4_callback *cb,
-		   struct rpc_rqst *rqstp)
+static int decode_cb_sequence4resok(struct xdr_stream *xdr,
+				    struct nfsd4_callback *cb)
 {
-	struct nfsd4_session *ses = cb->cb_clp->cl_cb_session;
+	struct nfsd4_session *session = cb->cb_clp->cl_cb_session;
 	struct nfs4_sessionid id;
 	int status;
-	u32 dummy;
 	__be32 *p;
+	u32 dummy;
 
-	if (cb->cb_minorversion == 0)
-		return 0;
-
-	status = decode_cb_op_hdr(xdr, OP_CB_SEQUENCE);
-	if (status)
-		return status;
+	status = -ESERVERFAULT;
 
 	/*
 	 * If the server returns different values for sessionID, slotID or
 	 * sequence number, the server is looney tunes.
 	 */
-	status = -ESERVERFAULT;
-
-	READ_BUF(NFS4_MAX_SESSIONID_LEN + 16);
+	p = xdr_inline_decode(xdr, NFS4_MAX_SESSIONID_LEN + 4 + 4 + 4 + 4);
+	if (unlikely(p == NULL))
+		goto out_overflow;
 	memcpy(id.data, p, NFS4_MAX_SESSIONID_LEN);
-	p += XDR_QUADLEN(NFS4_MAX_SESSIONID_LEN);
-	if (memcmp(id.data, ses->se_sessionid.data, NFS4_MAX_SESSIONID_LEN)) {
-		dprintk("%s Invalid session id\n", __func__);
+	if (memcmp(id.data, session->se_sessionid.data,
+					NFS4_MAX_SESSIONID_LEN) != 0) {
+		dprintk("NFS: %s Invalid session id\n", __func__);
 		goto out;
 	}
-	READ32(dummy);
-	if (dummy != ses->se_cb_seq_nr) {
-		dprintk("%s Invalid sequence number\n", __func__);
+	p += XDR_QUADLEN(NFS4_MAX_SESSIONID_LEN);
+
+	dummy = be32_to_cpup(p++);
+	if (dummy != session->se_cb_seq_nr) {
+		dprintk("NFS: %s Invalid sequence number\n", __func__);
 		goto out;
 	}
-	READ32(dummy); 	/* slotid must be 0 */
+
+	dummy = be32_to_cpup(p++);
 	if (dummy != 0) {
-		dprintk("%s Invalid slotid\n", __func__);
+		dprintk("NFS: %s Invalid slotid\n", __func__);
 		goto out;
 	}
-	/* FIXME: process highest slotid and target highest slotid */
+
+	/*
+	 * FIXME: process highest slotid and target highest slotid
+	 */
 	status = 0;
 out:
+	if (status)
+		nfsd4_mark_cb_fault(cb->cb_clp, status);
 	return status;
+out_overflow:
+	print_overflow_msg(__func__, xdr);
+	return -EIO;
 }
 
+static int decode_cb_sequence4res(struct xdr_stream *xdr,
+				  struct nfsd4_callback *cb)
+{
+	enum nfsstat4 nfserr;
+	int status;
+
+	if (cb->cb_minorversion == 0)
+		return 0;
 
-static int
-nfs4_xdr_dec_cb_null(struct rpc_rqst *req, __be32 *p)
+	status = decode_cb_op_status(xdr, OP_CB_SEQUENCE, &nfserr);
+	if (unlikely(status))
+		goto out;
+	if (unlikely(nfserr != NFS4_OK))
+		goto out_default;
+	status = decode_cb_sequence4resok(xdr, cb);
+out:
+	return status;
+out_default:
+	return nfs_cb_stat_to_errno(nfserr);
+}
+
+/*
+ * NFSv4.0 and NFSv4.1 XDR encode functions
+ *
+ * NFSv4.0 callback argument types are defined in section 15 of RFC
+ * 3530: "Network File System (NFS) version 4 Protocol" and section 20
+ * of RFC 5661:  "Network File System (NFS) Version 4 Minor Version 1
+ * Protocol".
+ */
+
+/*
+ * NB: Without this zero space reservation, callbacks over krb5p fail
+ */
+static void nfs4_xdr_enc_cb_null(struct rpc_rqst *req, struct xdr_stream *xdr,
+				 void *__unused)
+{
+	xdr_reserve_space(xdr, 0);
+}
+
+/*
+ * 20.2. Operation 4: CB_RECALL - Recall a Delegation
+ */
+static void nfs4_xdr_enc_cb_recall(struct rpc_rqst *req, struct xdr_stream *xdr,
+				   const struct nfsd4_callback *cb)
+{
+	const struct nfs4_delegation *args = cb->cb_op;
+	struct nfs4_cb_compound_hdr hdr = {
+		.ident = cb->cb_clp->cl_cb_ident,
+		.minorversion = cb->cb_minorversion,
+	};
+
+	encode_cb_compound4args(xdr, &hdr);
+	encode_cb_sequence4args(xdr, cb, &hdr);
+	encode_cb_recall4args(xdr, args, &hdr);
+	encode_cb_nops(&hdr);
+}
+
+
+/*
+ * NFSv4.0 and NFSv4.1 XDR decode functions
+ *
+ * NFSv4.0 callback result types are defined in section 15 of RFC
+ * 3530: "Network File System (NFS) version 4 Protocol" and section 20
+ * of RFC 5661:  "Network File System (NFS) Version 4 Minor Version 1
+ * Protocol".
+ */
+
+static int nfs4_xdr_dec_cb_null(struct rpc_rqst *req, struct xdr_stream *xdr,
+				void *__unused)
 {
 	return 0;
 }
 
-static int
-nfs4_xdr_dec_cb_recall(struct rpc_rqst *rqstp, __be32 *p,
-		struct nfsd4_callback *cb)
+/*
+ * 20.2. Operation 4: CB_RECALL - Recall a Delegation
+ */
+static int nfs4_xdr_dec_cb_recall(struct rpc_rqst *rqstp,
+				  struct xdr_stream *xdr,
+				  struct nfsd4_callback *cb)
 {
-	struct xdr_stream xdr;
 	struct nfs4_cb_compound_hdr hdr;
+	enum nfsstat4 nfserr;
 	int status;
 
-	xdr_init_decode(&xdr, &rqstp->rq_rcv_buf, p);
-	status = decode_cb_compound_hdr(&xdr, &hdr);
-	if (status)
+	status = decode_cb_compound4res(xdr, &hdr);
+	if (unlikely(status))
 		goto out;
-	if (cb) {
-		status = decode_cb_sequence(&xdr, cb, rqstp);
-		if (status)
+
+	if (cb != NULL) {
+		status = decode_cb_sequence4res(xdr, cb);
+		if (unlikely(status))
 			goto out;
 	}
-	status = decode_cb_op_hdr(&xdr, OP_CB_RECALL);
+
+	status = decode_cb_op_status(xdr, OP_CB_RECALL, &nfserr);
+	if (unlikely(status))
+		goto out;
+	if (unlikely(nfserr != NFS4_OK))
+		status = nfs_cb_stat_to_errno(nfserr);
 out:
 	return status;
 }
@@ -416,23 +555,23 @@ out:
 /*
  * RPC procedure tables
  */
-#define PROC(proc, call, argtype, restype)                              \
-[NFSPROC4_CLNT_##proc] = {                                      	\
-        .p_proc   = NFSPROC4_CB_##call,					\
-        .p_encode = (kxdrproc_t) nfs4_xdr_##argtype,                    \
-        .p_decode = (kxdrproc_t) nfs4_xdr_##restype,                    \
-        .p_arglen = NFS4_##argtype##_sz,                                \
-        .p_replen = NFS4_##restype##_sz,                                \
-        .p_statidx = NFSPROC4_CB_##call,				\
-	.p_name   = #proc,                                              \
-}
-
-static struct rpc_procinfo     nfs4_cb_procedures[] = {
-    PROC(CB_NULL,      NULL,     enc_cb_null,     dec_cb_null),
-    PROC(CB_RECALL,    COMPOUND,   enc_cb_recall,      dec_cb_recall),
+#define PROC(proc, call, argtype, restype)				\
+[NFSPROC4_CLNT_##proc] = {						\
+	.p_proc    = NFSPROC4_CB_##call,				\
+	.p_encode  = (kxdreproc_t)nfs4_xdr_enc_##argtype,		\
+	.p_decode  = (kxdrdproc_t)nfs4_xdr_dec_##restype,		\
+	.p_arglen  = NFS4_enc_##argtype##_sz,				\
+	.p_replen  = NFS4_dec_##restype##_sz,				\
+	.p_statidx = NFSPROC4_CB_##call,				\
+	.p_name    = #proc,						\
+}
+
+static struct rpc_procinfo nfs4_cb_procedures[] = {
+	PROC(CB_NULL,	NULL,		cb_null,	cb_null),
+	PROC(CB_RECALL,	COMPOUND,	cb_recall,	cb_recall),
 };
 
-static struct rpc_version       nfs_cb_version4 = {
+static struct rpc_version nfs_cb_version4 = {
 /*
  * Note on the callback rpc program version number: despite language in rfc
  * 5661 section 18.36.3 requiring servers to use 4 in this field, the
@@ -440,79 +579,134 @@ static struct rpc_version       nfs_cb_version4 = {
  * in practice that appears to be what implementations use.  The section
  * 18.36.3 language is expected to be fixed in an erratum.
  */
-        .number                 = 1,
-        .nrprocs                = ARRAY_SIZE(nfs4_cb_procedures),
-        .procs                  = nfs4_cb_procedures
+	.number			= 1,
+	.nrprocs		= ARRAY_SIZE(nfs4_cb_procedures),
+	.procs			= nfs4_cb_procedures
 };
 
-static struct rpc_version *	nfs_cb_version[] = {
+static const struct rpc_version *nfs_cb_version[] = {
 	&nfs_cb_version4,
 };
 
-static struct rpc_program cb_program;
+static const struct rpc_program cb_program;
 
 static struct rpc_stat cb_stats = {
-		.program	= &cb_program
+	.program		= &cb_program
 };
 
 #define NFS4_CALLBACK 0x40000000
-static struct rpc_program cb_program = {
-		.name 		= "nfs4_cb",
-		.number		= NFS4_CALLBACK,
-		.nrvers		= ARRAY_SIZE(nfs_cb_version),
-		.version	= nfs_cb_version,
-		.stats		= &cb_stats,
-		.pipe_dir_name  = "/nfsd4_cb",
+static const struct rpc_program cb_program = {
+	.name			= "nfs4_cb",
+	.number			= NFS4_CALLBACK,
+	.nrvers			= ARRAY_SIZE(nfs_cb_version),
+	.version		= nfs_cb_version,
+	.stats			= &cb_stats,
+	.pipe_dir_name		= "nfsd4_cb",
 };
 
-static int max_cb_time(void)
+static int max_cb_time(struct net *net)
+{
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	return max(nn->nfsd4_lease/10, (time_t)1) * HZ;
+}
+
+static struct rpc_cred *callback_cred;
+
+int set_callback_cred(void)
 {
-	return max(nfsd4_lease/10, (time_t)1) * HZ;
+	if (callback_cred)
+		return 0;
+	callback_cred = rpc_lookup_machine_cred("nfs");
+	if (!callback_cred)
+		return -ENOMEM;
+	return 0;
 }
 
-/* Reference counting, callback cleanup, etc., all look racy as heck.
- * And why is cl_cb_set an atomic? */
+static struct rpc_cred *get_backchannel_cred(struct nfs4_client *clp, struct rpc_clnt *client, struct nfsd4_session *ses)
+{
+	if (clp->cl_minorversion == 0) {
+		return get_rpccred(callback_cred);
+	} else {
+		struct rpc_auth *auth = client->cl_auth;
+		struct auth_cred acred = {};
+
+		acred.uid = ses->se_cb_sec.uid;
+		acred.gid = ses->se_cb_sec.gid;
+		return auth->au_ops->lookup_cred(client->cl_auth, &acred, 0);
+	}
+}
 
-int setup_callback_client(struct nfs4_client *clp, struct nfs4_cb_conn *conn)
+static struct rpc_clnt *create_backchannel_client(struct rpc_create_args *args)
 {
+	struct rpc_xprt *xprt;
+
+	if (args->protocol != XPRT_TRANSPORT_BC_TCP)
+		return rpc_create(args);
+
+	xprt = args->bc_xprt->xpt_bc_xprt;
+	if (xprt) {
+		xprt_get(xprt);
+		return rpc_create_xprt(args, xprt);
+	}
+
+	return rpc_create(args);
+}
+
+static int setup_callback_client(struct nfs4_client *clp, struct nfs4_cb_conn *conn, struct nfsd4_session *ses)
+{
+	int maxtime = max_cb_time(clp->net);
 	struct rpc_timeout	timeparms = {
-		.to_initval	= max_cb_time(),
+		.to_initval	= maxtime,
 		.to_retries	= 0,
+		.to_maxval	= maxtime,
 	};
 	struct rpc_create_args args = {
-		.net		= &init_net,
+		.net		= clp->net,
 		.address	= (struct sockaddr *) &conn->cb_addr,
 		.addrsize	= conn->cb_addrlen,
+		.saddress	= (struct sockaddr *) &conn->cb_saddr,
 		.timeout	= &timeparms,
 		.program	= &cb_program,
 		.version	= 0,
-		.authflavor	= clp->cl_flavor,
 		.flags		= (RPC_CLNT_CREATE_NOPING | RPC_CLNT_CREATE_QUIET),
 	};
 	struct rpc_clnt *client;
+	struct rpc_cred *cred;
 
 	if (clp->cl_minorversion == 0) {
-		if (!clp->cl_principal && (clp->cl_flavor >= RPC_AUTH_GSS_KRB5))
+		if (!clp->cl_cred.cr_principal &&
+				(clp->cl_cred.cr_flavor >= RPC_AUTH_GSS_KRB5))
 			return -EINVAL;
-		args.client_name = clp->cl_principal;
+		args.client_name = clp->cl_cred.cr_principal;
 		args.prognumber	= conn->cb_prog,
 		args.protocol = XPRT_TRANSPORT_TCP;
+		args.authflavor = clp->cl_cred.cr_flavor;
 		clp->cl_cb_ident = conn->cb_ident;
 	} else {
+		if (!conn->cb_xprt)
+			return -EINVAL;
+		clp->cl_cb_conn.cb_xprt = conn->cb_xprt;
+		clp->cl_cb_session = ses;
 		args.bc_xprt = conn->cb_xprt;
 		args.prognumber = clp->cl_cb_session->se_cb_prog;
 		args.protocol = XPRT_TRANSPORT_BC_TCP;
+		args.authflavor = ses->se_cb_sec.flavor;
 	}
 	/* Create RPC client */
-	client = rpc_create(&args);
+	client = create_backchannel_client(&args);
 	if (IS_ERR(client)) {
 		dprintk("NFSD: couldn't create callback client: %ld\n",
 			PTR_ERR(client));
 		return PTR_ERR(client);
 	}
+	cred = get_backchannel_cred(clp, client, ses);
+	if (IS_ERR(cred)) {
+		rpc_shutdown_client(client);
+		return PTR_ERR(cred);
+	}
 	clp->cl_cb_client = client;
+	clp->cl_cb_cred = cred;
 	return 0;
-
 }
 
 static void warn_no_callback_path(struct nfs4_client *clp, int reason)
@@ -521,14 +715,26 @@ static void warn_no_callback_path(struct nfs4_client *clp, int reason)
 		(int)clp->cl_name.len, clp->cl_name.data, reason);
 }
 
+static void nfsd4_mark_cb_down(struct nfs4_client *clp, int reason)
+{
+	clp->cl_cb_state = NFSD4_CB_DOWN;
+	warn_no_callback_path(clp, reason);
+}
+
+static void nfsd4_mark_cb_fault(struct nfs4_client *clp, int reason)
+{
+	clp->cl_cb_state = NFSD4_CB_FAULT;
+	warn_no_callback_path(clp, reason);
+}
+
 static void nfsd4_cb_probe_done(struct rpc_task *task, void *calldata)
 {
 	struct nfs4_client *clp = container_of(calldata, struct nfs4_client, cl_cb_null);
 
 	if (task->tk_status)
-		warn_no_callback_path(clp, task->tk_status);
+		nfsd4_mark_cb_down(clp, task->tk_status);
 	else
-		atomic_set(&clp->cl_cb_set, 1);
+		clp->cl_cb_state = NFSD4_CB_UP;
 }
 
 static const struct rpc_call_ops nfsd4_cb_probe_ops = {
@@ -537,20 +743,13 @@ static const struct rpc_call_ops nfsd4_cb_probe_ops = {
 	.rpc_call_done = nfsd4_cb_probe_done,
 };
 
-static struct rpc_cred *callback_cred;
+static struct workqueue_struct *callback_wq;
 
-int set_callback_cred(void)
+static void run_nfsd4_cb(struct nfsd4_callback *cb)
 {
-	if (callback_cred)
-		return 0;
-	callback_cred = rpc_lookup_machine_cred();
-	if (!callback_cred)
-		return -ENOMEM;
-	return 0;
+	queue_work(callback_wq, &cb->cb_work);
 }
 
-static struct workqueue_struct *callback_wq;
-
 static void do_probe_callback(struct nfs4_client *clp)
 {
 	struct nfsd4_callback *cb = &clp->cl_cb_null;
@@ -561,11 +760,10 @@ static void do_probe_callback(struct nfs4_client *clp)
 	cb->cb_msg.rpc_proc = &nfs4_cb_procedures[NFSPROC4_CLNT_CB_NULL];
 	cb->cb_msg.rpc_argp = NULL;
 	cb->cb_msg.rpc_resp = NULL;
-	cb->cb_msg.rpc_cred = callback_cred;
 
 	cb->cb_ops = &nfsd4_cb_probe_ops;
 
-	queue_work(callback_wq, &cb->cb_work);
+	run_nfsd4_cb(cb);
 }
 
 /*
@@ -574,14 +772,20 @@ static void do_probe_callback(struct nfs4_client *clp)
  */
 void nfsd4_probe_callback(struct nfs4_client *clp)
 {
-	set_bit(NFSD4_CLIENT_CB_UPDATE, &clp->cl_cb_flags);
+	clp->cl_cb_state = NFSD4_CB_UNKNOWN;
+	set_bit(NFSD4_CLIENT_CB_UPDATE, &clp->cl_flags);
 	do_probe_callback(clp);
 }
 
-void nfsd4_change_callback(struct nfs4_client *clp, struct nfs4_cb_conn *conn)
+void nfsd4_probe_callback_sync(struct nfs4_client *clp)
 {
-	BUG_ON(atomic_read(&clp->cl_cb_set));
+	nfsd4_probe_callback(clp);
+	flush_workqueue(callback_wq);
+}
 
+void nfsd4_change_callback(struct nfs4_client *clp, struct nfs4_cb_conn *conn)
+{
+	clp->cl_cb_state = NFSD4_CB_UNKNOWN;
 	spin_lock(&clp->cl_lock);
 	memcpy(&clp->cl_cb_conn, conn, sizeof(struct nfs4_cb_conn));
 	spin_unlock(&clp->cl_lock);
@@ -592,24 +796,14 @@ void nfsd4_change_callback(struct nfs4_client *clp, struct nfs4_cb_conn *conn)
  * If the slot is available, then mark it busy.  Otherwise, set the
  * thread for sleeping on the callback RPC wait queue.
  */
-static int nfsd41_cb_setup_sequence(struct nfs4_client *clp,
-		struct rpc_task *task)
+static bool nfsd41_cb_get_slot(struct nfs4_client *clp, struct rpc_task *task)
 {
-	u32 *ptr = (u32 *)clp->cl_cb_session->se_sessionid.data;
-	int status = 0;
-
-	dprintk("%s: %u:%u:%u:%u\n", __func__,
-		ptr[0], ptr[1], ptr[2], ptr[3]);
-
 	if (test_and_set_bit(0, &clp->cl_cb_slot_busy) != 0) {
 		rpc_sleep_on(&clp->cl_cb_waitq, task, NULL);
 		dprintk("%s slot is busy\n", __func__);
-		status = -EAGAIN;
-		goto out;
+		return false;
 	}
-out:
-	dprintk("%s status=%d\n", __func__, status);
-	return status;
+	return true;
 }
 
 /*
@@ -619,31 +813,28 @@ out:
 static void nfsd4_cb_prepare(struct rpc_task *task, void *calldata)
 {
 	struct nfsd4_callback *cb = calldata;
-	struct nfs4_delegation *dp = container_of(cb, struct nfs4_delegation, dl_recall);
-	struct nfs4_client *clp = dp->dl_client;
+	struct nfs4_client *clp = cb->cb_clp;
 	u32 minorversion = clp->cl_minorversion;
-	int status = 0;
 
 	cb->cb_minorversion = minorversion;
 	if (minorversion) {
-		status = nfsd41_cb_setup_sequence(clp, task);
-		if (status) {
-			if (status != -EAGAIN) {
-				/* terminate rpc task */
-				task->tk_status = status;
-				task->tk_action = NULL;
-			}
+		if (!nfsd41_cb_get_slot(clp, task))
 			return;
-		}
 	}
+	spin_lock(&clp->cl_lock);
+	if (list_empty(&cb->cb_per_client)) {
+		/* This is the first call, not a restart */
+		cb->cb_done = false;
+		list_add(&cb->cb_per_client, &clp->cl_callbacks);
+	}
+	spin_unlock(&clp->cl_lock);
 	rpc_call_start(task);
 }
 
 static void nfsd4_cb_done(struct rpc_task *task, void *calldata)
 {
 	struct nfsd4_callback *cb = calldata;
-	struct nfs4_delegation *dp = container_of(cb, struct nfs4_delegation, dl_recall);
-	struct nfs4_client *clp = dp->dl_client;
+	struct nfs4_client *clp = cb->cb_clp;
 
 	dprintk("%s: minorversion=%d\n", __func__,
 		clp->cl_minorversion);
@@ -666,20 +857,23 @@ static void nfsd4_cb_recall_done(struct rpc_task *task, void *calldata)
 {
 	struct nfsd4_callback *cb = calldata;
 	struct nfs4_delegation *dp = container_of(cb, struct nfs4_delegation, dl_recall);
-	struct nfs4_client *clp = dp->dl_client;
+	struct nfs4_client *clp = cb->cb_clp;
 	struct rpc_clnt *current_rpc_client = clp->cl_cb_client;
 
 	nfsd4_cb_done(task, calldata);
 
-	if (current_rpc_client == NULL) {
-		/* We're shutting down; give up. */
-		/* XXX: err, or is it ok just to fall through
-		 * and rpc_restart_call? */
+	if (current_rpc_client != task->tk_client) {
+		/* We're shutting down or changing cl_cb_client; leave
+		 * it to nfsd4_process_cb_update to restart the call if
+		 * necessary. */
 		return;
 	}
 
+	if (cb->cb_done)
+		return;
 	switch (task->tk_status) {
 	case 0:
+		cb->cb_done = true;
 		return;
 	case -EBADHANDLE:
 	case -NFS4ERR_BAD_STATEID:
@@ -688,32 +882,30 @@ static void nfsd4_cb_recall_done(struct rpc_task *task, void *calldata)
 		break;
 	default:
 		/* Network partition? */
-		atomic_set(&clp->cl_cb_set, 0);
-		warn_no_callback_path(clp, task->tk_status);
-		if (current_rpc_client != task->tk_client) {
-			/* queue a callback on the new connection: */
-			atomic_inc(&dp->dl_count);
-			nfsd4_cb_recall(dp);
-			return;
-		}
+		nfsd4_mark_cb_down(clp, task->tk_status);
 	}
 	if (dp->dl_retries--) {
 		rpc_delay(task, 2*HZ);
 		task->tk_status = 0;
 		rpc_restart_call_prepare(task);
 		return;
-	} else {
-		atomic_set(&clp->cl_cb_set, 0);
-		warn_no_callback_path(clp, task->tk_status);
 	}
+	nfsd4_mark_cb_down(clp, task->tk_status);
+	cb->cb_done = true;
 }
 
 static void nfsd4_cb_recall_release(void *calldata)
 {
 	struct nfsd4_callback *cb = calldata;
+	struct nfs4_client *clp = cb->cb_clp;
 	struct nfs4_delegation *dp = container_of(cb, struct nfs4_delegation, dl_recall);
 
-	nfs4_put_delegation(dp);
+	if (cb->cb_done) {
+		spin_lock(&clp->cl_lock);
+		list_del(&cb->cb_per_client);
+		spin_unlock(&clp->cl_lock);
+		nfs4_put_delegation(dp);
+	}
 }
 
 static const struct rpc_call_ops nfsd4_cb_recall_ops = {
@@ -738,7 +930,7 @@ void nfsd4_destroy_callback_queue(void)
 /* must be called under the state lock */
 void nfsd4_shutdown_callback(struct nfs4_client *clp)
 {
-	set_bit(NFSD4_CLIENT_KILL, &clp->cl_cb_flags);
+	set_bit(NFSD4_CLIENT_CB_KILL, &clp->cl_flags);
 	/*
 	 * Note this won't actually result in a null callback;
 	 * instead, nfsd4_do_callback_rpc() will detect the killed
@@ -748,16 +940,33 @@ void nfsd4_shutdown_callback(struct nfs4_client *clp)
 	flush_workqueue(callback_wq);
 }
 
-void nfsd4_release_cb(struct nfsd4_callback *cb)
+static void nfsd4_release_cb(struct nfsd4_callback *cb)
 {
 	if (cb->cb_ops->rpc_release)
 		cb->cb_ops->rpc_release(cb);
 }
 
-void nfsd4_process_cb_update(struct nfsd4_callback *cb)
+/* requires cl_lock: */
+static struct nfsd4_conn * __nfsd4_find_backchannel(struct nfs4_client *clp)
+{
+	struct nfsd4_session *s;
+	struct nfsd4_conn *c;
+
+	list_for_each_entry(s, &clp->cl_sessions, se_perclnt) {
+		list_for_each_entry(c, &s->se_conns, cn_persession) {
+			if (c->cn_flags & NFS4_CDFC4_BACK)
+				return c;
+		}
+	}
+	return NULL;
+}
+
+static void nfsd4_process_cb_update(struct nfsd4_callback *cb)
 {
 	struct nfs4_cb_conn conn;
 	struct nfs4_client *clp = cb->cb_clp;
+	struct nfsd4_session *ses = NULL;
+	struct nfsd4_conn *c;
 	int err;
 
 	/*
@@ -767,31 +976,48 @@ void nfsd4_process_cb_update(struct nfsd4_callback *cb)
 	if (clp->cl_cb_client) {
 		rpc_shutdown_client(clp->cl_cb_client);
 		clp->cl_cb_client = NULL;
+		put_rpccred(clp->cl_cb_cred);
+		clp->cl_cb_cred = NULL;
 	}
-	if (test_bit(NFSD4_CLIENT_KILL, &clp->cl_cb_flags))
+	if (clp->cl_cb_conn.cb_xprt) {
+		svc_xprt_put(clp->cl_cb_conn.cb_xprt);
+		clp->cl_cb_conn.cb_xprt = NULL;
+	}
+	if (test_bit(NFSD4_CLIENT_CB_KILL, &clp->cl_flags))
 		return;
 	spin_lock(&clp->cl_lock);
 	/*
 	 * Only serialized callback code is allowed to clear these
 	 * flags; main nfsd code can only set them:
 	 */
-	BUG_ON(!clp->cl_cb_flags);
-	clear_bit(NFSD4_CLIENT_CB_UPDATE, &clp->cl_cb_flags);
+	BUG_ON(!(clp->cl_flags & NFSD4_CLIENT_CB_FLAG_MASK));
+	clear_bit(NFSD4_CLIENT_CB_UPDATE, &clp->cl_flags);
 	memcpy(&conn, &cb->cb_clp->cl_cb_conn, sizeof(struct nfs4_cb_conn));
+	c = __nfsd4_find_backchannel(clp);
+	if (c) {
+		svc_xprt_get(c->cn_xprt);
+		conn.cb_xprt = c->cn_xprt;
+		ses = c->cn_session;
+	}
 	spin_unlock(&clp->cl_lock);
 
-	err = setup_callback_client(clp, &conn);
-	if (err)
-		warn_no_callback_path(clp, err);
+	err = setup_callback_client(clp, &conn, ses);
+	if (err) {
+		nfsd4_mark_cb_down(clp, err);
+		return;
+	}
+	/* Yay, the callback channel's back! Restart any callbacks: */
+	list_for_each_entry(cb, &clp->cl_callbacks, cb_per_client)
+		run_nfsd4_cb(cb);
 }
 
-void nfsd4_do_callback_rpc(struct work_struct *w)
+static void nfsd4_do_callback_rpc(struct work_struct *w)
 {
 	struct nfsd4_callback *cb = container_of(w, struct nfsd4_callback, cb_work);
 	struct nfs4_client *clp = cb->cb_clp;
 	struct rpc_clnt *clnt;
 
-	if (clp->cl_cb_flags)
+	if (clp->cl_flags & NFSD4_CLIENT_CB_FLAG_MASK)
 		nfsd4_process_cb_update(cb);
 
 	clnt = clp->cl_cb_client;
@@ -800,24 +1026,32 @@ void nfsd4_do_callback_rpc(struct work_struct *w)
 		nfsd4_release_cb(cb);
 		return;
 	}
+	cb->cb_msg.rpc_cred = clp->cl_cb_cred;
 	rpc_call_async(clnt, &cb->cb_msg, RPC_TASK_SOFT | RPC_TASK_SOFTCONN,
 			cb->cb_ops, cb);
 }
 
+void nfsd4_init_callback(struct nfsd4_callback *cb)
+{
+	INIT_WORK(&cb->cb_work, nfsd4_do_callback_rpc);
+}
+
 void nfsd4_cb_recall(struct nfs4_delegation *dp)
 {
 	struct nfsd4_callback *cb = &dp->dl_recall;
+	struct nfs4_client *clp = dp->dl_stid.sc_client;
 
 	dp->dl_retries = 1;
 	cb->cb_op = dp;
-	cb->cb_clp = dp->dl_client;
+	cb->cb_clp = clp;
 	cb->cb_msg.rpc_proc = &nfs4_cb_procedures[NFSPROC4_CLNT_CB_RECALL];
 	cb->cb_msg.rpc_argp = cb;
 	cb->cb_msg.rpc_resp = cb;
-	cb->cb_msg.rpc_cred = callback_cred;
 
 	cb->cb_ops = &nfsd4_cb_recall_ops;
-	dp->dl_retries = 1;
 
-	queue_work(callback_wq, &dp->dl_recall.cb_work);
+	INIT_LIST_HEAD(&cb->cb_per_client);
+	cb->cb_done = true;
+
+	run_nfsd4_cb(&dp->dl_recall);
 }