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?
> 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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