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 <bfields@xxxxxxxxxx> wrote:
> > From: "J. Bruce Fields" <bfields@xxxxxxxxxx>
> >
> > 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 <bfields@xxxxxxxxxx>
> > ---
> > 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
> >
> > --
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