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Message-ID: <CAN-5tyEEfJ5p=NUaj+ubzCijq+d9vxT9EBVHvwQYgF=CMtrNTw@mail.gmail.com>
Date: Sat, 9 Nov 2024 13:50:51 -0500
From: Olga Kornievskaia <aglo@...ch.edu>
To: Jeff Layton <jlayton@...nel.org>
Cc: Chuck Lever <chuck.lever@...cle.com>, Neil Brown <neilb@...e.de>, 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 Tue, Nov 5, 2024 at 7:31 PM Jeff Layton <jlayton@...nel.org> 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;
> + }
> + 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;
> 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;
> +
> 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)
Are there some values that are known not to work? I was experimenting
with values and set it to 2 and 4 and the kernel oopsed. I understand
it's not a configurable value but it would still be good to know the
expectations...
[ 198.625021] Unable to handle kernel paging request at virtual
address dfff800020000000
[ 198.625870] KASAN: probably user-memory-access in range
[0x0000000100000000-0x0000000100000007]
[ 198.626444] Mem abort info:
[ 198.626630] ESR = 0x0000000096000005
[ 198.626882] EC = 0x25: DABT (current EL), IL = 32 bits
[ 198.627234] SET = 0, FnV = 0
[ 198.627441] EA = 0, S1PTW = 0
[ 198.627627] FSC = 0x05: level 1 translation fault
[ 198.627859] Data abort info:
[ 198.628000] ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
[ 198.628272] CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[ 198.628619] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[ 198.628967] [dfff800020000000] address between user and kernel address ranges
[ 198.629438] Internal error: Oops: 0000000096000005 [#1] SMP
[ 198.629806] Modules linked in: rpcsec_gss_krb5 nfsv4 dns_resolver
nfs netfs nfnetlink_queue nfnetlink_log nfnetlink bluetooth cfg80211
rpcrdma rdma_cm iw_cm ib_cm ib_core nfsd auth_rpcgss nfs_acl lockd
grace isofs uinput snd_seq_dummy snd_hrtimer vsock_loopback
vmw_vsock_virtio_transport_common qrtr rfkill vmw_vsock_vmci_transport
vsock sunrpc vfat fat snd_hda_codec_generic snd_hda_intel
snd_intel_dspcfg snd_hda_codec snd_hda_core snd_hwdep snd_seq uvcvideo
videobuf2_vmalloc snd_seq_device videobuf2_memops uvc videobuf2_v4l2
videodev snd_pcm videobuf2_common mc snd_timer snd vmw_vmci soundcore
xfs libcrc32c vmwgfx drm_ttm_helper ttm nvme drm_kms_helper
crct10dif_ce nvme_core ghash_ce sha2_ce sha256_arm64 sha1_ce drm
nvme_auth sr_mod cdrom e1000e sg fuse
[ 198.633799] CPU: 5 UID: 0 PID: 6081 Comm: nfsd Kdump: loaded Not
tainted 6.12.0-rc6+ #47
[ 198.634345] Hardware name: VMware, Inc. VMware20,1/VBSA, BIOS
VMW201.00V.21805430.BA64.2305221830 05/22/2023
[ 198.635014] pstate: 11400005 (nzcV daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[ 198.635492] pc : nfsd4_sequence+0x5a0/0x1f60 [nfsd]
[ 198.635798] lr : nfsd4_sequence+0x340/0x1f60 [nfsd]
[ 198.636065] sp : ffff8000884977e0
[ 198.636234] x29: ffff800088497910 x28: ffff0000b1b39280 x27: ffff0000ab508128
[ 198.636624] x26: ffff0000b1b39298 x25: ffff0000b1b39290 x24: ffff0000a65e1c64
[ 198.637049] x23: 1fffe000212e6804 x22: ffff000109734024 x21: 1ffff00011092f16
[ 198.637472] x20: ffff00010aed8000 x19: ffff000109734000 x18: 1fffe0002de20c8b
[ 198.637883] x17: 0100000000000000 x16: 1ffff0000fcef234 x15: 1fffe000212e600f
[ 198.638286] x14: ffff80007e779000 x13: ffff80007e7791a0 x12: 0000000000000000
[ 198.638697] x11: ffff0000a65e1c38 x10: ffff00010aedaca0 x9 : 1fffe000215db594
[ 198.639110] x8 : 1fffe00014cbc387 x7 : ffff0000a65e1c03 x6 : ffff0000a65e1c00
[ 198.639541] x5 : ffff0000a65e1c00 x4 : 0000000020000000 x3 : 0000000100000001
[ 198.639962] x2 : ffff000109730060 x1 : 0000000000000003 x0 : dfff800000000000
[ 198.640332] Call trace:
[ 198.640460] nfsd4_sequence+0x5a0/0x1f60 [nfsd]
[ 198.640715] nfsd4_proc_compound+0xb94/0x23b0 [nfsd]
[ 198.640997] nfsd_dispatch+0x22c/0x718 [nfsd]
[ 198.641260] svc_process_common+0x8e8/0x1968 [sunrpc]
[ 198.641566] svc_process+0x3d4/0x7e0 [sunrpc]
[ 198.641827] svc_handle_xprt+0x828/0xe10 [sunrpc]
[ 198.642108] svc_recv+0x2cc/0x6a8 [sunrpc]
[ 198.642346] nfsd+0x270/0x400 [nfsd]
[ 198.642562] kthread+0x288/0x310
[ 198.642745] ret_from_fork+0x10/0x20
[ 198.642937] Code: f2fbffe0 f9003be4 f94007e2 52800061 (38e06880)
[ 198.643267] SMP: stopping secondary CPUs
> +
> /*
> * 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>
>
>
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