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Message-ID: <a572abe16d1e186dbb2b6ea66a1de8bafb967dcd.camel@kernel.org>
Date: Tue, 12 Nov 2024 20:03:54 -0500
From: Jeff Layton <jlayton@...nel.org>
To: NeilBrown <neilb@...e.de>
Cc: Chuck Lever <chuck.lever@...cle.com>, Dai Ngo <Dai.Ngo@...cle.com>, Tom
Talpey <tom@...pey.com>, Olga Kornievskaia <okorniev@...hat.com>,
linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] nfsd: allow for up to 32 callback session slots
On Wed, 2024-11-13 at 11:07 +1100, NeilBrown wrote:
> On Wed, 06 Nov 2024, Jeff Layton wrote:
> > nfsd currently only uses a single slot in the callback channel, which is
> > proving to be a bottleneck in some cases. Widen the callback channel to
> > a max of 32 slots (subject to the client's target_maxreqs value).
> >
> > Change the cb_holds_slot boolean to an integer that tracks the current
> > slot number (with -1 meaning "unassigned"). Move the callback slot
> > tracking info into the session. Add a new u32 that acts as a bitmap to
> > track which slots are in use, and a u32 to track the latest callback
> > target_slotid that the client reports. To protect the new fields, add
> > a new per-session spinlock (the se_lock). Fix nfsd41_cb_get_slot to always
> > search for the lowest slotid (using ffs()).
> >
> > Finally, convert the session->se_cb_seq_nr field into an array of
> > counters and add the necessary handling to ensure that the seqids get
> > reset at the appropriate times.
> >
> > Signed-off-by: Jeff Layton <jlayton@...nel.org>
> > Signed-off-by: Chuck Lever <chuck.lever@...cle.com>
> > ---
> > v3 has a bug that Olga hit in testing. This version should fix the wait
> > when the slot table is full. Olga, if you're able to test this one, it
> > would be much appreciated.
> > ---
> > Changes in v4:
> > - Fix the wait for a slot in nfsd41_cb_get_slot()
> > - Link to v3: https://lore.kernel.org/r/20241030-bcwide-v3-0-c2df49a26c45@kernel.org
> >
> > Changes in v3:
> > - add patch to convert se_flags to single se_dead bool
> > - fix off-by-one bug in handling of NFSD_BC_SLOT_TABLE_MAX
> > - don't reject target highest slot value of 0
> > - Link to v2: https://lore.kernel.org/r/20241029-bcwide-v2-1-e9010b6ef55d@kernel.org
> >
> > Changes in v2:
> > - take cl_lock when fetching fields from session to be encoded
> > - use fls() instead of bespoke highest_unset_index()
> > - rename variables in several functions with more descriptive names
> > - clamp limit of for loop in update_cb_slot_table()
> > - re-add missing rpc_wake_up_queued_task() call
> > - fix slotid check in decode_cb_sequence4resok()
> > - add new per-session spinlock
> > ---
> > fs/nfsd/nfs4callback.c | 113 ++++++++++++++++++++++++++++++++++++-------------
> > fs/nfsd/nfs4state.c | 11 +++--
> > fs/nfsd/state.h | 15 ++++---
> > fs/nfsd/trace.h | 2 +-
> > 4 files changed, 101 insertions(+), 40 deletions(-)
> >
> > diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
> > index e38fa834b3d91333acf1425eb14c644e5d5f2601..47a678333907eaa92db305dada503704c34c15b2 100644
> > --- a/fs/nfsd/nfs4callback.c
> > +++ b/fs/nfsd/nfs4callback.c
> > @@ -406,6 +406,19 @@ encode_cb_getattr4args(struct xdr_stream *xdr, struct nfs4_cb_compound_hdr *hdr,
> > hdr->nops++;
> > }
> >
> > +static u32 highest_slotid(struct nfsd4_session *ses)
> > +{
> > + u32 idx;
> > +
> > + spin_lock(&ses->se_lock);
> > + idx = fls(~ses->se_cb_slot_avail);
> > + if (idx > 0)
> > + --idx;
> > + idx = max(idx, ses->se_cb_highest_slot);
> > + spin_unlock(&ses->se_lock);
> > + return idx;
> > +}
> > +
> > /*
> > * CB_SEQUENCE4args
> > *
> > @@ -432,15 +445,35 @@ static void encode_cb_sequence4args(struct xdr_stream *xdr,
> > 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++ = cpu_to_be32(session->se_cb_seq_nr[cb->cb_held_slot]); /* csa_sequenceid */
> > + *p++ = cpu_to_be32(cb->cb_held_slot); /* csa_slotid */
> > + *p++ = cpu_to_be32(highest_slotid(session)); /* csa_highest_slotid */
> > *p++ = xdr_zero; /* csa_cachethis */
> > xdr_encode_empty_array(p); /* csa_referring_call_lists */
> >
> > hdr->nops++;
> > }
> >
> > +static void update_cb_slot_table(struct nfsd4_session *ses, u32 target)
> > +{
> > + /* No need to do anything if nothing changed */
> > + if (likely(target == READ_ONCE(ses->se_cb_highest_slot)))
> > + return;
> > +
> > + spin_lock(&ses->se_lock);
> > + if (target > ses->se_cb_highest_slot) {
> > + int i;
> > +
> > + target = min(target, NFSD_BC_SLOT_TABLE_MAX);
> > +
> > + /* Growing the slot table. Reset any new sequences to 1 */
> > + for (i = ses->se_cb_highest_slot + 1; i <= target; ++i)
> > + ses->se_cb_seq_nr[i] = 1;
>
> Where is the justification in the RFC for resetting the sequence
> numbers?
>
RFC 8881, 18.36:
[...]
Once the session is created, the first SEQUENCE or CB_SEQUENCE received
on a slot MUST have a sequence ID equal to 1; if not, the replier MUST
return NFS4ERR_SEQ_MISORDERED.
There is also some verbiage in 20.10.6.1.
> The csr_target_highest_slotid from the client - which is the value passed as
> 'target' is defined as:
>
> the highest slot ID the client would prefer the server use on a
> future CB_SEQUENCE operation.
>
> This is not "the highest slot ID for which the client is remembering
> sequence numbers".
>
> If we can get rid of this, then I think the need for se_lock evaporates.
> Allocating a new slow would be
>
> do {
> idx = ffs(ses->se_cb_slot_avail) - 1;
> } while (is_valid(idx) && test_and_set_bit(idx, &ses->se_sb_slot_avail));
>
> where is_valid(idX) is idx >= 0 && idx <= ses->se_sb_highest_slot
>
That certainly would be better.
Maybe it's not required to start the seqid for a new slot at 1? If a
new slot can start its sequence counter at an arbitrary value then we
should be able to do this.
>
> > + }
> > + ses->se_cb_highest_slot = target;
> > + spin_unlock(&ses->se_lock);
> > +}
> > +
> > /*
> > * CB_SEQUENCE4resok
> > *
> > @@ -468,7 +501,7 @@ static int decode_cb_sequence4resok(struct xdr_stream *xdr,
> > struct nfsd4_session *session = cb->cb_clp->cl_cb_session;
> > int status = -ESERVERFAULT;
> > __be32 *p;
> > - u32 dummy;
> > + u32 seqid, slotid, target;
> >
> > /*
> > * If the server returns different values for sessionID, slotID or
> > @@ -484,21 +517,22 @@ static int decode_cb_sequence4resok(struct xdr_stream *xdr,
> > }
> > p += XDR_QUADLEN(NFS4_MAX_SESSIONID_LEN);
> >
> > - dummy = be32_to_cpup(p++);
> > - if (dummy != session->se_cb_seq_nr) {
> > + seqid = be32_to_cpup(p++);
> > + if (seqid != session->se_cb_seq_nr[cb->cb_held_slot]) {
> > dprintk("NFS: %s Invalid sequence number\n", __func__);
> > goto out;
> > }
> >
> > - dummy = be32_to_cpup(p++);
> > - if (dummy != 0) {
> > + slotid = be32_to_cpup(p++);
> > + if (slotid != cb->cb_held_slot) {
> > dprintk("NFS: %s Invalid slotid\n", __func__);
> > goto out;
> > }
> >
> > - /*
> > - * FIXME: process highest slotid and target highest slotid
> > - */
> > + p++; // ignore current highest slot value
> > +
> > + target = be32_to_cpup(p++);
> > + update_cb_slot_table(session, target);
> > status = 0;
> > out:
> > cb->cb_seq_status = status;
> > @@ -1203,6 +1237,22 @@ void nfsd4_change_callback(struct nfs4_client *clp, struct nfs4_cb_conn *conn)
> > spin_unlock(&clp->cl_lock);
> > }
> >
> > +static int grab_slot(struct nfsd4_session *ses)
> > +{
> > + int idx;
> > +
> > + spin_lock(&ses->se_lock);
> > + idx = ffs(ses->se_cb_slot_avail) - 1;
> > + if (idx < 0 || idx > ses->se_cb_highest_slot) {
> > + spin_unlock(&ses->se_lock);
> > + return -1;
> > + }
> > + /* clear the bit for the slot */
> > + ses->se_cb_slot_avail &= ~BIT(idx);
> > + spin_unlock(&ses->se_lock);
> > + return idx;
> > +}
> > +
> > /*
> > * There's currently a single callback channel slot.
> > * If the slot is available, then mark it busy. Otherwise, set the
> > @@ -1211,28 +1261,32 @@ void nfsd4_change_callback(struct nfs4_client *clp, struct nfs4_cb_conn *conn)
> > static bool nfsd41_cb_get_slot(struct nfsd4_callback *cb, struct rpc_task *task)
> > {
> > struct nfs4_client *clp = cb->cb_clp;
> > + struct nfsd4_session *ses = clp->cl_cb_session;
> >
> > - if (!cb->cb_holds_slot &&
> > - test_and_set_bit(0, &clp->cl_cb_slot_busy) != 0) {
> > + if (cb->cb_held_slot >= 0)
> > + return true;
> > + cb->cb_held_slot = grab_slot(ses);
> > + if (cb->cb_held_slot < 0) {
> > rpc_sleep_on(&clp->cl_cb_waitq, task, NULL);
> > /* Race breaker */
> > - if (test_and_set_bit(0, &clp->cl_cb_slot_busy) != 0) {
> > - dprintk("%s slot is busy\n", __func__);
> > + cb->cb_held_slot = grab_slot(ses);
> > + if (cb->cb_held_slot < 0)
> > return false;
> > - }
> > rpc_wake_up_queued_task(&clp->cl_cb_waitq, task);
> > }
> > - cb->cb_holds_slot = true;
> > return true;
> > }
> >
> > static void nfsd41_cb_release_slot(struct nfsd4_callback *cb)
> > {
> > struct nfs4_client *clp = cb->cb_clp;
> > + struct nfsd4_session *ses = clp->cl_cb_session;
> >
> > - if (cb->cb_holds_slot) {
> > - cb->cb_holds_slot = false;
> > - clear_bit(0, &clp->cl_cb_slot_busy);
> > + if (cb->cb_held_slot >= 0) {
> > + spin_lock(&ses->se_lock);
> > + ses->se_cb_slot_avail |= BIT(cb->cb_held_slot);
> > + spin_unlock(&ses->se_lock);
> > + cb->cb_held_slot = -1;
> > rpc_wake_up_next(&clp->cl_cb_waitq);
> > }
> > }
> > @@ -1249,8 +1303,8 @@ static void nfsd41_destroy_cb(struct nfsd4_callback *cb)
> > }
> >
> > /*
> > - * TODO: cb_sequence should support referring call lists, cachethis, multiple
> > - * slots, and mark callback channel down on communication errors.
> > + * TODO: cb_sequence should support referring call lists, cachethis,
> > + * and mark callback channel down on communication errors.
> > */
> > static void nfsd4_cb_prepare(struct rpc_task *task, void *calldata)
> > {
> > @@ -1292,7 +1346,7 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback
> > return true;
> > }
> >
> > - if (!cb->cb_holds_slot)
> > + if (cb->cb_held_slot < 0)
> > goto need_restart;
> >
> > /* This is the operation status code for CB_SEQUENCE */
> > @@ -1306,10 +1360,10 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback
> > * If CB_SEQUENCE returns an error, then the state of the slot
> > * (sequence ID, cached reply) MUST NOT change.
> > */
> > - ++session->se_cb_seq_nr;
> > + ++session->se_cb_seq_nr[cb->cb_held_slot];
> > break;
> > case -ESERVERFAULT:
> > - ++session->se_cb_seq_nr;
> > + ++session->se_cb_seq_nr[cb->cb_held_slot];
> > nfsd4_mark_cb_fault(cb->cb_clp);
> > ret = false;
> > break;
> > @@ -1335,17 +1389,16 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback
> > case -NFS4ERR_BADSLOT:
> > goto retry_nowait;
> > case -NFS4ERR_SEQ_MISORDERED:
> > - if (session->se_cb_seq_nr != 1) {
> > - session->se_cb_seq_nr = 1;
> > + if (session->se_cb_seq_nr[cb->cb_held_slot] != 1) {
> > + session->se_cb_seq_nr[cb->cb_held_slot] = 1;
>
> This is weird ... why do we reset the seq_nr to 1 when we get
> SEQ_MISORDERED?? Git logs don't shed any light :-(
>
The above verbiage from 18.36 might hint that this is the right thing
to do, but it's a little vague.
> > goto retry_nowait;
> > }
> > break;
> > default:
> > nfsd4_mark_cb_fault(cb->cb_clp);
> > }
> > - nfsd41_cb_release_slot(cb);
> > -
> > trace_nfsd_cb_free_slot(task, cb);
> > + nfsd41_cb_release_slot(cb);
> >
> > if (RPC_SIGNALLED(task))
> > goto need_restart;
> > @@ -1565,7 +1618,7 @@ void nfsd4_init_cb(struct nfsd4_callback *cb, struct nfs4_client *clp,
> > INIT_WORK(&cb->cb_work, nfsd4_run_cb_work);
> > cb->cb_status = 0;
> > cb->cb_need_restart = false;
> > - cb->cb_holds_slot = false;
> > + cb->cb_held_slot = -1;
> > }
> >
> > /**
> > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> > index baf7994131fe1b0a4715174ba943fd2a9882aa12..75557e7cc9265517f51952563beaa4cfe8adcc3f 100644
> > --- a/fs/nfsd/nfs4state.c
> > +++ b/fs/nfsd/nfs4state.c
> > @@ -2002,6 +2002,9 @@ static struct nfsd4_session *alloc_session(struct nfsd4_channel_attrs *fattrs,
> > }
> >
> > memcpy(&new->se_fchannel, fattrs, sizeof(struct nfsd4_channel_attrs));
> > + new->se_cb_slot_avail = ~0U;
> > + new->se_cb_highest_slot = battrs->maxreqs - 1;
> > + spin_lock_init(&new->se_lock);
> > return new;
> > out_free:
> > while (i--)
> > @@ -2132,11 +2135,14 @@ static void init_session(struct svc_rqst *rqstp, struct nfsd4_session *new, stru
> >
> > INIT_LIST_HEAD(&new->se_conns);
> >
> > - new->se_cb_seq_nr = 1;
> > + atomic_set(&new->se_ref, 0);
> > new->se_dead = false;
> > new->se_cb_prog = cses->callback_prog;
> > new->se_cb_sec = cses->cb_sec;
> > - atomic_set(&new->se_ref, 0);
> > +
> > + for (idx = 0; idx < NFSD_BC_SLOT_TABLE_MAX; ++idx)
> > + new->se_cb_seq_nr[idx] = 1;
>
> That should be "<= NFSD_BC_SLOT_TABLE_MAX"
MAX in this case is the maximum slot index, so this is correct for the
code as it stands today. I'm fine with redefining the constant to track
the size of the slot table instead. We could also make the existing
code more clear by just renaming the existing constant to
NFSD_BC_SLOT_INDEX_MAX.
>
> I don't think *_MAX is a good choice of name. It is the maximum number
> of slots (no) or the maximum slot number (yes).
> I think *_SIZE would be a better name - the size of the table that we
> allocate. 32.
> Looking at where the const is used in current nfsd-next:
>
> target = min(target, NFSD_BC_SLOT_TABLE_SIZE - 1
>
> new->se_cb_highest_slot = min(battrs->maxreqs,
> NFSD_BC_SLOT_TABLE_SIZE) - 1;
>
> for (idx = 0; idx < NFSD_BC_SLOT_TABLE_SIZE; ++idx)
>
> #define NFSD_BC_SLOT_TABLE_SIZE (sizeof(u32) * 8)
>
> u32 se_cb_seq_nr[NFSD_BC_SLOT_TABLE_SIZE];
>
> which is a slight reduction in the number of "+/-1" adjustments.
>
>
>
>
> > +
> > idx = hash_sessionid(&new->se_sessionid);
> > list_add(&new->se_hash, &nn->sessionid_hashtbl[idx]);
> > spin_lock(&clp->cl_lock);
> > @@ -3159,7 +3165,6 @@ static struct nfs4_client *create_client(struct xdr_netobj name,
> > kref_init(&clp->cl_nfsdfs.cl_ref);
> > nfsd4_init_cb(&clp->cl_cb_null, clp, NULL, NFSPROC4_CLNT_CB_NULL);
> > clp->cl_time = ktime_get_boottime_seconds();
> > - clear_bit(0, &clp->cl_cb_slot_busy);
> > copy_verf(clp, verf);
> > memcpy(&clp->cl_addr, sa, sizeof(struct sockaddr_storage));
> > clp->cl_cb_session = NULL;
> > diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
> > index d22e4f2c9039324a0953a9e15a3c255fb8ee1a44..848d023cb308f0b69916c4ee34b09075708f0de3 100644
> > --- a/fs/nfsd/state.h
> > +++ b/fs/nfsd/state.h
> > @@ -71,8 +71,8 @@ struct nfsd4_callback {
> > struct work_struct cb_work;
> > int cb_seq_status;
> > int cb_status;
> > + int cb_held_slot;
> > bool cb_need_restart;
> > - bool cb_holds_slot;
> > };
> >
> > struct nfsd4_callback_ops {
> > @@ -307,6 +307,9 @@ struct nfsd4_conn {
> > unsigned char cn_flags;
> > };
> >
> > +/* Highest slot index that nfsd implements in NFSv4.1+ backchannel */
> > +#define NFSD_BC_SLOT_TABLE_MAX (sizeof(u32) * 8 - 1)
> > +
> > /*
> > * Representation of a v4.1+ session. These are refcounted in a similar fashion
> > * to the nfs4_client. References are only taken when the server is actively
> > @@ -314,6 +317,10 @@ struct nfsd4_conn {
> > */
> > struct nfsd4_session {
> > atomic_t se_ref;
> > + spinlock_t se_lock;
> > + u32 se_cb_slot_avail; /* bitmap of available slots */
> > + u32 se_cb_highest_slot; /* highest slot client wants */
> > + u32 se_cb_prog;
> > bool se_dead;
> > struct list_head se_hash; /* hash by sessionid */
> > struct list_head se_perclnt;
> > @@ -322,8 +329,7 @@ struct nfsd4_session {
> > struct nfsd4_channel_attrs se_fchannel;
> > struct nfsd4_cb_sec se_cb_sec;
> > struct list_head se_conns;
> > - u32 se_cb_prog;
> > - u32 se_cb_seq_nr;
> > + u32 se_cb_seq_nr[NFSD_BC_SLOT_TABLE_MAX + 1];
> > struct nfsd4_slot *se_slots[]; /* forward channel slots */
> > };
> >
> > @@ -457,9 +463,6 @@ struct nfs4_client {
> > */
> > struct dentry *cl_nfsd_info_dentry;
> >
> > - /* for nfs41 callbacks */
> > - /* We currently support a single back channel with a single slot */
> > - unsigned long cl_cb_slot_busy;
> > struct rpc_wait_queue cl_cb_waitq; /* backchannel callers may */
> > /* wait here for slots */
> > struct net *net;
> > diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> > index f318898cfc31614b5a84a4867e18c2b3a07122c9..a9c17186b6892f1df8d7f7b90e250c2913ab23fe 100644
> > --- a/fs/nfsd/trace.h
> > +++ b/fs/nfsd/trace.h
> > @@ -1697,7 +1697,7 @@ TRACE_EVENT(nfsd_cb_free_slot,
> > __entry->cl_id = sid->clientid.cl_id;
> > __entry->seqno = sid->sequence;
> > __entry->reserved = sid->reserved;
> > - __entry->slot_seqno = session->se_cb_seq_nr;
> > + __entry->slot_seqno = session->se_cb_seq_nr[cb->cb_held_slot];
> > ),
> > TP_printk(SUNRPC_TRACE_TASK_SPECIFIER
> > " sessionid=%08x:%08x:%08x:%08x new slot seqno=%u",
> >
> > ---
> > base-commit: 3c16aac09d20f9005fbb0e737b3ec520bbb5badd
> > change-id: 20241025-bcwide-6bd7e4b63db2
> >
> > Best regards,
> > --
> > Jeff Layton <jlayton@...nel.org>
> >
> >
>
> NeilBrown
--
Jeff Layton <jlayton@...nel.org>
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