From 87597731488105dd1ab921a95e39bb62e1abe668 Mon Sep 17 00:00:00 2001 From: Rick Macklem Date: Mon, 26 Apr 2021 16:24:10 -0700 Subject: [PATCH] nfsd: fix the slot sequence# when a callback fails Commit 4281bfec3628 patched the server so that the callback session slot would be free'd for reuse when a callback attempt fails. However, this can often result in the sequence# for the session slot to be advanced such that the client end will reply NFSERR_SEQMISORDERED. To avoid the NFSERR_SEQMISORDERED client reply, this patch negates the sequence# advance for the case where the callback has failed. The common case is a failed back channel, where the callback cannot be sent to the client, and not advancing the sequence# is correct for this case. For the uncommon case where the client's reply to the callback is lost, not advancing the sequence# will indicate to the client that the next callback is a retry and not a new callback. But, since the FreeBSD server always sets "csa_cachethis" false in the callback sequence operation, a retry and a new callback should be handled the same way by the client, so this should not matter. Until you have this patch in your NFSv4.1/4.2 server, you should consider avoiding the use of delegations. Even with this patch, interoperation with the Linux NFSv4.1/4.2 client in kernel versions prior to 5.3 can result in frequent 15second delays if delegations are enabled. This occurs because, for kernels prior to 5.3, the Linux client does a TCP reconnect every time it sees multiple concurrent callbacks and then it takes 15seconds to recover the back channel after doing so. MFC after: 2 weeks --- sys/fs/nfs/nfs_commonkrpc.c | 4 ++-- sys/fs/nfs/nfs_commonsubs.c | 4 +++- sys/fs/nfs/nfs_var.h | 2 +- sys/fs/nfsserver/nfs_nfsdstate.c | 23 ++++++++++++++++++++--- 4 files changed, 26 insertions(+), 7 deletions(-) diff --git a/sys/fs/nfs/nfs_commonkrpc.c b/sys/fs/nfs/nfs_commonkrpc.c index daf8082fa1c..6e766abcf4b 100644 --- a/sys/fs/nfs/nfs_commonkrpc.c +++ b/sys/fs/nfs/nfs_commonkrpc.c @@ -871,7 +871,7 @@ tryagain: sep->nfsess_slotseq[nd->nd_slotid] += 10; mtx_unlock(&sep->nfsess_mtx); /* And free the slot. */ - nfsv4_freeslot(sep, nd->nd_slotid); + nfsv4_freeslot(sep, nd->nd_slotid, false); } NFSINCRGLOBAL(nfsstatsv1.rpcinvalid); error = ENXIO; @@ -1108,7 +1108,7 @@ tryagain: if ((nd->nd_flag & ND_NFSV4) != 0) { /* Free the slot, as required. */ if (freeslot != -1) - nfsv4_freeslot(sep, freeslot); + nfsv4_freeslot(sep, freeslot, false); /* * If this op is Putfh, throw its results away. */ diff --git a/sys/fs/nfs/nfs_commonsubs.c b/sys/fs/nfs/nfs_commonsubs.c index a30ee458e06..539cbbbde7d 100644 --- a/sys/fs/nfs/nfs_commonsubs.c +++ b/sys/fs/nfs/nfs_commonsubs.c @@ -4811,7 +4811,7 @@ nfsv4_sequencelookup(struct nfsmount *nmp, struct nfsclsession *sep, * Free a session slot. */ void -nfsv4_freeslot(struct nfsclsession *sep, int slot) +nfsv4_freeslot(struct nfsclsession *sep, int slot, bool resetseq) { uint64_t bitval; @@ -4819,6 +4819,8 @@ nfsv4_freeslot(struct nfsclsession *sep, int slot) if (slot > 0) bitval <<= slot; mtx_lock(&sep->nfsess_mtx); + if (resetseq) + sep->nfsess_slotseq[slot]--; if ((bitval & sep->nfsess_slots) == 0) printf("freeing free slot!!\n"); sep->nfsess_slots &= ~bitval; diff --git a/sys/fs/nfs/nfs_var.h b/sys/fs/nfs/nfs_var.h index 201c5a5fc2b..f23d5605044 100644 --- a/sys/fs/nfs/nfs_var.h +++ b/sys/fs/nfs/nfs_var.h @@ -355,7 +355,7 @@ void nfsv4_setsequence(struct nfsmount *, struct nfsrv_descript *, struct nfsclsession *, int); int nfsv4_sequencelookup(struct nfsmount *, struct nfsclsession *, int *, int *, uint32_t *, uint8_t *); -void nfsv4_freeslot(struct nfsclsession *, int); +void nfsv4_freeslot(struct nfsclsession *, int, bool); struct ucred *nfsrv_getgrpscred(struct ucred *); struct nfsdevice *nfsv4_findmirror(struct nfsmount *); void nfsm_set(struct nfsrv_descript *, u_int); diff --git a/sys/fs/nfsserver/nfs_nfsdstate.c b/sys/fs/nfsserver/nfs_nfsdstate.c index 430f09844b8..3aebddad096 100644 --- a/sys/fs/nfsserver/nfs_nfsdstate.c +++ b/sys/fs/nfsserver/nfs_nfsdstate.c @@ -4572,7 +4572,8 @@ nfsrv_docallback(struct nfsclient *clp, int procnum, nfsv4stateid_t *stateidp, if ((clp->lc_flags & LCL_NFSV41) != 0) { error = ECONNREFUSED; if (procnum != NFSV4PROC_CBNULL) - nfsv4_freeslot(&sep->sess_cbsess, slotpos); + nfsv4_freeslot(&sep->sess_cbsess, slotpos, + true); nfsrv_freesession(sep, NULL); } else if (nd->nd_procnum == NFSV4PROC_CBNULL) error = newnfs_connect(NULL, &clp->lc_req, cred, @@ -4604,8 +4605,24 @@ nfsrv_docallback(struct nfsclient *clp, int procnum, nfsv4stateid_t *stateidp, error = ECONNREFUSED; } NFSD_DEBUG(4, "aft newnfs_request=%d\n", error); - if (error != 0 && procnum != NFSV4PROC_CBNULL) - nfsv4_freeslot(&sep->sess_cbsess, slotpos); + if (error != 0 && procnum != NFSV4PROC_CBNULL) { + /* + * It is likely that the callback was never + * processed by the client and, as such, + * the sequence# for the session slot needs + * to be backed up by one to avoid a + * NFSERR_SEQMISORDERED error reply. + * For the unlikely case where the callback + * was processed by the client, this will + * make the next callback on the slot + * appear to be a retry. + * Since callbacks never specify that the + * reply be cached, this "apparent retry" + * should not be a problem. + */ + nfsv4_freeslot(&sep->sess_cbsess, slotpos, + true); + } nfsrv_freesession(sep, NULL); } else error = newnfs_request(nd, NULL, clp, &clp->lc_req,