Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:49801 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752022AbdJSSRV (ORCPT ); Thu, 19 Oct 2017 14:17:21 -0400 Date: Thu, 19 Oct 2017 14:17:19 -0400 From: "J. Bruce Fields" To: Olga Kornievskaia Cc: Trond Myklebust , linux-nfs Subject: Re: [PATCH 1/2] nfsd4: fix cached replies to solo SEQUENCE compounds Message-ID: <20171019181718.GF16942@parsley.fieldses.org> References: <1508361919-30495-1-git-send-email-bfields@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Sender: linux-nfs-owner@vger.kernel.org List-ID: On Thu, Oct 19, 2017 at 01:21:46PM -0400, Olga Kornievskaia wrote: > On Wed, Oct 18, 2017 at 5:25 PM, J. Bruce Fields wrote: > > From: "J. Bruce Fields" > > > > Currently our handling of 4.1+ requests without "cachethis" set is > > confusing and not quite correct. > > > > Suppose a client sends a compound consisting of only a single SEQUENCE > > op, and it matches the seqid in a session slot (so it's a retry), but > > the previous request with that seqid did not have "cachethis" set. > > > > The obvious thing to do might be to return NFS4ERR_RETRY_UNCACHED_REP, > > but the protocol only allows that to be returned on the op following the > > SEQUENCE, and there is no such op in this case. > > > > The protocol permits us to cache replies even if the client didn't ask > > us to. And it's easy to do so in the case of solo SEQUENCE compounds. > > > > So, when we get a solo SEQUENCE, we can either return the previously > > cached reply or NFSERR_SEQ_FALSE_RETRY if we notice it differs in some > > way from the original call. > > I'm confused in my testing the error was SEQ_MISORDERED and not > SEQ_FALSE_RETRY error? Yes, I must have a typo somewhere, but I haven't spotted it yet. That was with both patches applied? --b. > > > Currently, we're returning a corrupt reply in the case a solo SEQUENCE > > matches a previous compound with more ops. This actually matters > > because the Linux client recently started doing this as a way to recover > > from lost replies to idempotent operations in the case the process doing > > the original reply was killed: in that case it's difficult to keep the > > original arguments around to do a real retry, and the client no longer > > cares what the result is anyway, but it would like to make sure that the > > slot's sequence id has been incremented, and the solo SEQUENCE assures > > that: if the server never got the original reply, it will increment the > > sequence id. If it did get the original reply, it won't increment, and > > nothing else that about the reply really matters much. But we can at > > least attempt to return valid xdr! > > > > Signed-off-by: J. Bruce Fields > > --- > > fs/nfsd/nfs4state.c | 23 ++++++++++++++++------- > > fs/nfsd/state.h | 1 + > > fs/nfsd/xdr4.h | 13 +++++++++++-- > > 3 files changed, 28 insertions(+), 9 deletions(-) > > > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > > index 9db8a19cceaa..7bd3ad88b85c 100644 > > --- a/fs/nfsd/nfs4state.c > > +++ b/fs/nfsd/nfs4state.c > > @@ -2292,14 +2292,15 @@ nfsd4_store_cache_entry(struct nfsd4_compoundres *resp) > > > > dprintk("--> %s slot %p\n", __func__, slot); > > > > - slot->sl_opcnt = resp->opcnt; > > - slot->sl_status = resp->cstate.status; > > - > > slot->sl_flags |= NFSD4_SLOT_INITIALIZED; > > - if (nfsd4_not_cached(resp)) { > > - slot->sl_datalen = 0; > > + if (!nfsd4_cache_this(resp)) { > > + slot->sl_flags &= !NFSD4_SLOT_CACHED; > > return; > > } > > + slot->sl_flags |= NFSD4_SLOT_CACHED; > > + slot->sl_opcnt = resp->opcnt; > > + slot->sl_status = resp->cstate.status; > > + > > base = resp->cstate.data_offset; > > slot->sl_datalen = buf->len - base; > > if (read_bytes_from_xdr_buf(buf, base, slot->sl_data, slot->sl_datalen)) > > @@ -2326,8 +2327,16 @@ nfsd4_enc_sequence_replay(struct nfsd4_compoundargs *args, > > op = &args->ops[resp->opcnt - 1]; > > nfsd4_encode_operation(resp, op); > > > > - /* Return nfserr_retry_uncached_rep in next operation. */ > > - if (args->opcnt > 1 && !(slot->sl_flags & NFSD4_SLOT_CACHETHIS)) { > > + if (slot->sl_flags & NFSD4_SLOT_CACHED) > > + return op->status; > > + if (args->opcnt == 1) { > > + /* > > + * The original operation wasn't a solo sequence--we > > + * always cache those--so this retry must not match the > > + * original: > > + */ > > + op->status = nfserr_seq_false_retry; > > + } else { > > op = &args->ops[resp->opcnt++]; > > op->status = nfserr_retry_uncached_rep; > > nfsd4_encode_operation(resp, op); > > diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h > > index 005c911b34ac..2488b7df1b35 100644 > > --- a/fs/nfsd/state.h > > +++ b/fs/nfsd/state.h > > @@ -174,6 +174,7 @@ struct nfsd4_slot { > > #define NFSD4_SLOT_INUSE (1 << 0) > > #define NFSD4_SLOT_CACHETHIS (1 << 1) > > #define NFSD4_SLOT_INITIALIZED (1 << 2) > > +#define NFSD4_SLOT_CACHED (1 << 3) > > u8 sl_flags; > > char sl_data[]; > > }; > > diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h > > index 1e4edbf70052..bc29511b6405 100644 > > --- a/fs/nfsd/xdr4.h > > +++ b/fs/nfsd/xdr4.h > > @@ -649,9 +649,18 @@ static inline bool nfsd4_is_solo_sequence(struct nfsd4_compoundres *resp) > > return resp->opcnt == 1 && args->ops[0].opnum == OP_SEQUENCE; > > } > > > > -static inline bool nfsd4_not_cached(struct nfsd4_compoundres *resp) > > +/* > > + * The session reply cache only needs to cache replies that the client > > + * actually asked us to. But it's almost free for us to cache compounds > > + * consisting of only a SEQUENCE op, so we may as well cache those too. > > + * Also, the protocol doesn't give us a convenient response in the case > > + * of a replay of a solo SEQUENCE op that wasn't cached > > + * (RETRY_UNCACHED_REP can only be returned in the second op of a > > + * compound). > > + */ > > +static inline bool nfsd4_cache_this(struct nfsd4_compoundres *resp) > > { > > - return !(resp->cstate.slot->sl_flags & NFSD4_SLOT_CACHETHIS) > > + return (resp->cstate.slot->sl_flags & NFSD4_SLOT_CACHETHIS) > > || nfsd4_is_solo_sequence(resp); > > } > > > > -- > > 2.13.5 > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html