[PATCH 2/2] nfsd: allow for more callback session slots

Jeff Layton
2024-10-28T14:26:37Z

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. While they are part of the
session, the fields are protected by the cl_lock.

Fix nfsd41_cb_get_slot to always search for the lowest slotid (using
ffs()), and change it to continually retry until there is a slot
available.

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@kernel.org>
---
fs/nfsd/nfs4callback.c | 107 +++++++++++++++++++++++++++++++++++--------------
fs/nfsd/nfs4state.c | 7 +++-
fs/nfsd/state.h | 12 +++---
fs/nfsd/trace.h | 2 +-
4 files changed, 89 insertions(+), 39 deletions(-)

diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index e38fa834b3d91333acf1425eb14c644e5d5f2601..64b85b164125b244494f9805840a0d8a1ccb4c1b 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -406,6 +406,16 @@ encode_cb_getattr4args(struct xdr_stream *xdr, struct nfs4_cb_compound_hdr *hdr,
hdr->nops++;
}

+static u32 highest_unset_index(u32 word)
+{
+ int i;
+
+ for (i = sizeof(word) * 8 - 1; i > 0; --i)
+ if (!(word & BIT(i)))
+ return i;
+ return 0;
+}
+
/*
* CB_SEQUENCE4args
*
@@ -432,15 +442,38 @@ 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(max(highest_unset_index(session->se_cb_slot_avail),
+ session->se_cb_highest_slot)); /* 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 highest)
+{
+ /* No need to do anything if nothing changed */
+ if (likely(highest == READ_ONCE(ses->se_cb_highest_slot)))
+ return;
+
+ spin_lock(&ses->se_client->cl_lock);
+ /* If growing the slot table, reset any new sequences to 1 */
+ if (highest > ses->se_cb_highest_slot) {
+ int i;
+
+ for (i = ses->se_cb_highest_slot; i <= highest; ++i) {
+ /* beyond the end of the array? */
+ if (i >= NFSD_BC_SLOT_TABLE_MAX)
+ break;
+ ses->se_cb_seq_nr[i] = 1;
+ }
+ }
+ ses->se_cb_highest_slot = highest;
+ spin_unlock(&ses->se_client->cl_lock);
+}
+
/*
* CB_SEQUENCE4resok
*
@@ -485,7 +518,7 @@ 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) {
+ if (dummy != session->se_cb_seq_nr[cb->cb_held_slot]) {
dprintk("NFS: %s Invalid sequence number\n", __func__);
goto out;
}
@@ -496,9 +529,15 @@ static int decode_cb_sequence4resok(struct xdr_stream *xdr,
goto out;
}

- /*
- * FIXME: process highest slotid and target highest slotid
- */
+ p++; // ignore current highest slot value
+
+ dummy = be32_to_cpup(p++);
+ if (dummy == 0) {
+ dprintk("NFS: %s Invalid target highest slotid\n", __func__);
+ goto out;
+ }
+
+ update_cb_slot_table(session, dummy);
status = 0;
out:
cb->cb_seq_status = status;
@@ -1208,31 +1247,38 @@ void nfsd4_change_callback(struct nfs4_client *clp, struct nfs4_cb_conn *conn)
* If the slot is available, then mark it busy. Otherwise, set the
* thread for sleeping on the callback RPC wait queue.
*/
-static bool nfsd41_cb_get_slot(struct nfsd4_callback *cb, struct rpc_task *task)
+static void 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;
+ int idx;

- if (!cb->cb_holds_slot &&
- test_and_set_bit(0, &clp->cl_cb_slot_busy) != 0) {
+ if (cb->cb_held_slot >= 0)
+ return;
+retry:
+ spin_lock(&clp->cl_lock);
+ idx = ffs(ses->se_cb_slot_avail) - 1;
+ if (idx < 0 || idx > ses->se_cb_highest_slot) {
+ spin_unlock(&clp->cl_lock);
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__);
- return false;
- }
- rpc_wake_up_queued_task(&clp->cl_cb_waitq, task);
+ goto retry;
}
- cb->cb_holds_slot = true;
- return true;
+ /* clear the bit for the slot */
+ ses->se_cb_slot_avail &= ~BIT(idx);
+ spin_unlock(&clp->cl_lock);
+ cb->cb_held_slot = idx;
}

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(&clp->cl_lock);
+ ses->se_cb_slot_avail |= BIT(cb->cb_held_slot);
+ spin_unlock(&clp->cl_lock);
+ cb->cb_held_slot = -1;
rpc_wake_up_next(&clp->cl_cb_waitq);
}
}
@@ -1265,8 +1311,8 @@ static void nfsd4_cb_prepare(struct rpc_task *task, void *calldata)
trace_nfsd_cb_rpc_prepare(clp);
cb->cb_seq_status = 1;
cb->cb_status = 0;
- if (minorversion && !nfsd41_cb_get_slot(cb, task))
- return;
+ if (minorversion)
+ nfsd41_cb_get_slot(cb, task);
rpc_call_start(task);
}

@@ -1292,7 +1338,7 @@ 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 +1352,10 @@ 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 +1381,16 @@ 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 +1610,7 @@ 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 5b718b349396f1aecd0ad4c63b2f43342841bbd4..20a0d40202e40eed1c84d5d6c0a85b908804a6ba 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -2002,6 +2002,8 @@ 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;
return new;
out_free:
while (i--)
@@ -2132,7 +2134,9 @@ 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;
+ for (idx = 0; idx < NFSD_BC_SLOT_TABLE_MAX; ++idx)
+ new->se_cb_seq_nr[idx] = 1;
+
new->se_flags = cses->flags;
new->se_cb_prog = cses->callback_prog;
new->se_cb_sec = cses->cb_sec;
@@ -3159,7 +3163,6 @@ 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 41cda86fea1f6166a0fd0215d3d458c93ced3e6a..2987c362bdd56251e736879dc89302ada2259be8 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;
};

+/* Max number of slots that the server will use in the backchannel */
+#define NFSD_BC_SLOT_TABLE_MAX 32
+
/*
* 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
@@ -325,7 +328,9 @@ struct nfsd4_session {
struct nfsd4_cb_sec se_cb_sec;
struct list_head se_conns;
u32 se_cb_prog;
- u32 se_cb_seq_nr;
+ u32 se_cb_slot_avail; /* bitmap of available slots */
+ u32 se_cb_highest_slot; /* highest slot client wants */
+ u32 se_cb_seq_nr[NFSD_BC_SLOT_TABLE_MAX];
struct nfsd4_slot *se_slots[]; /* forward channel slots */
};

@@ -459,9 +464,6 @@ 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",

--
2.47.0