[PATCH 6/8] afs: Split the usage count on struct afs_server

From: David Howells
Date: Fri Apr 24 2020 - 11:20:42 EST

Split the usage count on the afs_server struct to have an active count that
registers who's actually using it separately from the reference count on
the object.

This allows a future patch to dispatch polling probes without advancing the
"unuse" time into the future each time we emit a probe, which would
otherwise prevent unused server records from expiring.

Included in this:

(1) The latter part of afs_destroy_server() in which the RCU destruction
of afs_server objects is invoked and the outstanding server count is
decremented is split out into __afs_put_server().

(2) afs_put_server() now calls __afs_put_server() rather then setting the
management timer.

(3) The calls begun by afs_fs_give_up_all_callbacks() and
afs_fs_get_capabilities() can now take a ref on the server record, so
afs_destroy_server() can just drop its ref and needn't wait for the
completion of these calls. They'll put the ref when they're done.

(4) Because of (3), afs_fs_probe_done() no longer needs to wake up
afs_destroy_server() with server->probe_outstanding.

(5) afs_gc_servers can be simplified. It only needs to check if
server->active is 0 rather than playing games with the refcount.

(6) afs_manage_servers() can propose a server for gc if usage == 0 rather
than if ref == 1. The gc is effected by (5).

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---

fs/afs/cmservice.c | 4 +
fs/afs/fs_probe.c | 1
fs/afs/fsclient.c | 5 +
fs/afs/internal.h | 8 ++
fs/afs/proc.c | 9 +--
fs/afs/rxrpc.c | 2 -
fs/afs/server.c | 151 +++++++++++++++++++++++++++++---------------
fs/afs/server_list.c | 4 +
include/trace/events/afs.h | 18 +++--
9 files changed, 131 insertions(+), 71 deletions(-)

diff --git a/fs/afs/cmservice.c b/fs/afs/cmservice.c
index 380ad5ace7cf..7dcbca3bf828 100644
--- a/fs/afs/cmservice.c
+++ b/fs/afs/cmservice.c
@@ -268,7 +268,9 @@ static void SRXAFSCB_CallBack(struct work_struct *work)
* to maintain cache coherency.
*/
if (call->server) {
- trace_afs_server(call->server, atomic_read(&call->server->usage),
+ trace_afs_server(call->server,
+ atomic_read(&call->server->ref),
+ atomic_read(&call->server->active),
afs_server_trace_callback);
afs_break_callbacks(call->server, call->count, call->request);
}
diff --git a/fs/afs/fs_probe.c b/fs/afs/fs_probe.c
index a587767b6ae1..d458b0adfce5 100644
--- a/fs/afs/fs_probe.c
+++ b/fs/afs/fs_probe.c
@@ -16,7 +16,6 @@ static bool afs_fs_probe_done(struct afs_server *server)
if (!atomic_dec_and_test(&server->probe_outstanding))
return false;

- wake_up_var(&server->probe_outstanding);
clear_bit_unlock(AFS_SERVER_FL_PROBING, &server->flags);
wake_up_bit(&server->flags, AFS_SERVER_FL_PROBING);
return true;
diff --git a/fs/afs/fsclient.c b/fs/afs/fsclient.c
index 68fc46634346..7384fb545eb4 100644
--- a/fs/afs/fsclient.c
+++ b/fs/afs/fsclient.c
@@ -1842,7 +1842,7 @@ int afs_fs_give_up_all_callbacks(struct afs_net *net,
bp = call->request;
*bp++ = htonl(FSGIVEUPALLCALLBACKS);

- /* Can't take a ref on server */
+ call->server = afs_use_server(server, afs_server_trace_give_up_cb);
afs_make_call(ac, call, GFP_NOFS);
return afs_wait_for_call_to_complete(call, ac);
}
@@ -1924,7 +1924,7 @@ struct afs_call *afs_fs_get_capabilities(struct afs_net *net,
return ERR_PTR(-ENOMEM);

call->key = key;
- call->server = afs_get_server(server, afs_server_trace_get_caps);
+ call->server = afs_use_server(server, afs_server_trace_get_caps);
call->server_index = server_index;
call->upgrade = true;
call->async = true;
@@ -1934,7 +1934,6 @@ struct afs_call *afs_fs_get_capabilities(struct afs_net *net,
bp = call->request;
*bp++ = htonl(FSGETCAPABILITIES);

- /* Can't take a ref on server */
trace_afs_make_fs_call(call, NULL);
afs_make_call(ac, call, GFP_NOFS);
return call;
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index ee17c868ad2c..cb70e1c234cc 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -498,7 +498,7 @@ struct afs_server {
struct hlist_node addr6_link; /* Link in net->fs_addresses6 */
struct hlist_node proc_link; /* Link in net->fs_proc */
struct afs_server *gc_next; /* Next server in manager's list */
- time64_t put_time; /* Time at which last put */
+ time64_t unuse_time; /* Time at which last unused */
unsigned long flags;
#define AFS_SERVER_FL_NOT_READY 1 /* The record is not ready for use */
#define AFS_SERVER_FL_NOT_FOUND 2 /* VL server says no such server */
@@ -512,7 +512,8 @@ struct afs_server {
#define AFS_SERVER_FL_NO_RM2 10 /* Fileserver doesn't support YFS.RemoveFile2 */
#define AFS_SERVER_FL_HAVE_EPOCH 11 /* ->epoch is valid */
#define AFS_SERVER_FL_NEEDS_UPDATE 12 /* Fileserver address list is out of date */
- atomic_t usage;
+ atomic_t ref; /* Object refcount */
+ atomic_t active; /* Active user count */
u32 addr_version; /* Address list version */
u32 cm_epoch; /* Server RxRPC epoch */
unsigned int debug_id; /* Debugging ID for traces */
@@ -1244,6 +1245,9 @@ extern struct afs_server *afs_find_server(struct afs_net *,
extern struct afs_server *afs_find_server_by_uuid(struct afs_net *, const uuid_t *);
extern struct afs_server *afs_lookup_server(struct afs_cell *, struct key *, const uuid_t *, u32);
extern struct afs_server *afs_get_server(struct afs_server *, enum afs_server_trace);
+extern struct afs_server *afs_use_server(struct afs_server *, enum afs_server_trace);
+extern void afs_unuse_server(struct afs_net *, struct afs_server *, enum afs_server_trace);
+extern void afs_unuse_server_notime(struct afs_net *, struct afs_server *, enum afs_server_trace);
extern void afs_put_server(struct afs_net *, struct afs_server *, enum afs_server_trace);
extern void afs_manage_servers(struct work_struct *);
extern void afs_servers_timer(struct timer_list *);
diff --git a/fs/afs/proc.c b/fs/afs/proc.c
index 468e1713bce1..9bce7898cd7d 100644
--- a/fs/afs/proc.c
+++ b/fs/afs/proc.c
@@ -378,19 +378,20 @@ static int afs_proc_servers_show(struct seq_file *m, void *v)
int i;

if (v == SEQ_START_TOKEN) {
- seq_puts(m, "UUID USE ADDR\n");
+ seq_puts(m, "UUID REF ACT ADDR\n");
return 0;
}

server = list_entry(v, struct afs_server, proc_link);
alist = rcu_dereference(server->addresses);
- seq_printf(m, "%pU %3d %pISpc%s\n",
+ seq_printf(m, "%pU %3d %3d %pISpc%s\n",
&server->uuid,
- atomic_read(&server->usage),
+ atomic_read(&server->ref),
+ atomic_read(&server->active),
&alist->addrs[0].transport,
alist->preferred == 0 ? "*" : "");
for (i = 1; i < alist->nr_addrs; i++)
- seq_printf(m, " %pISpc%s\n",
+ seq_printf(m, " %pISpc%s\n",
&alist->addrs[i].transport,
alist->preferred == i ? "*" : "");
return 0;
diff --git a/fs/afs/rxrpc.c b/fs/afs/rxrpc.c
index 1ecc67da6c1a..ab2962fff1fb 100644
--- a/fs/afs/rxrpc.c
+++ b/fs/afs/rxrpc.c
@@ -183,7 +183,7 @@ void afs_put_call(struct afs_call *call)
if (call->type->destructor)
call->type->destructor(call);

- afs_put_server(call->net, call->server, afs_server_trace_put_call);
+ afs_unuse_server_notime(call->net, call->server, afs_server_trace_put_call);
afs_put_cb_interest(call->net, call->cbi);
afs_put_addrlist(call->alist);
kfree(call->request);
diff --git a/fs/afs/server.c b/fs/afs/server.c
index 9e50ccde5d37..4969a681f8f5 100644
--- a/fs/afs/server.c
+++ b/fs/afs/server.c
@@ -25,6 +25,10 @@ static void afs_dec_servers_outstanding(struct afs_net *net)
wake_up_var(&net->servers_outstanding);
}

+static struct afs_server *afs_maybe_use_server(struct afs_server *,
+ enum afs_server_trace);
+static void __afs_put_server(struct afs_net *, struct afs_server *);
+
/*
* Find a server by one of its addresses.
*/
@@ -40,7 +44,7 @@ struct afs_server *afs_find_server(struct afs_net *net,

do {
if (server)
- afs_put_server(net, server, afs_server_trace_put_find_rsq);
+ afs_unuse_server_notime(net, server, afs_server_trace_put_find_rsq);
server = NULL;
read_seqbegin_or_lock(&net->fs_addr_lock, &seq);

@@ -78,9 +82,9 @@ struct afs_server *afs_find_server(struct afs_net *net,
}

server = NULL;
+ continue;
found:
- if (server && !atomic_inc_not_zero(&server->usage))
- server = NULL;
+ server = afs_maybe_use_server(server, afs_server_trace_get_by_addr);

} while (need_seqretry(&net->fs_addr_lock, seq));

@@ -91,7 +95,7 @@ struct afs_server *afs_find_server(struct afs_net *net,
}

/*
- * Look up a server by its UUID
+ * Look up a server by its UUID and mark it active.
*/
struct afs_server *afs_find_server_by_uuid(struct afs_net *net, const uuid_t *uuid)
{
@@ -107,7 +111,7 @@ struct afs_server *afs_find_server_by_uuid(struct afs_net *net, const uuid_t *uu
* changes.
*/
if (server)
- afs_put_server(net, server, afs_server_trace_put_uuid_rsq);
+ afs_unuse_server(net, server, afs_server_trace_put_uuid_rsq);
server = NULL;

read_seqbegin_or_lock(&net->fs_lock, &seq);
@@ -122,7 +126,7 @@ struct afs_server *afs_find_server_by_uuid(struct afs_net *net, const uuid_t *uu
} else if (diff > 0) {
p = p->rb_right;
} else {
- afs_get_server(server, afs_server_trace_get_by_uuid);
+ afs_use_server(server, afs_server_trace_get_by_uuid);
break;
}

@@ -198,7 +202,7 @@ static struct afs_server *afs_install_server(struct afs_net *net,
}

/*
- * allocate a new server record
+ * Allocate a new server record and mark it active.
*/
static struct afs_server *afs_alloc_server(struct afs_net *net,
const uuid_t *uuid,
@@ -212,7 +216,8 @@ static struct afs_server *afs_alloc_server(struct afs_net *net,
if (!server)
goto enomem;

- atomic_set(&server->usage, 1);
+ atomic_set(&server->ref, 1);
+ atomic_set(&server->active, 1);
server->debug_id = atomic_inc_return(&afs_server_debug_id);
RCU_INIT_POINTER(server->addresses, alist);
server->addr_version = alist->version;
@@ -224,7 +229,7 @@ static struct afs_server *afs_alloc_server(struct afs_net *net,
spin_lock_init(&server->probe_lock);

afs_inc_servers_outstanding(net);
- trace_afs_server(server, 1, afs_server_trace_alloc);
+ trace_afs_server(server, 1, 1, afs_server_trace_alloc);
_leave(" = %p", server);
return server;

@@ -292,7 +297,6 @@ struct afs_server *afs_lookup_server(struct afs_cell *cell, struct key *key,
kfree(candidate);
}

- _leave(" = %p{%d}", server, atomic_read(&server->usage));
return server;
}

@@ -328,9 +332,38 @@ void afs_servers_timer(struct timer_list *timer)
struct afs_server *afs_get_server(struct afs_server *server,
enum afs_server_trace reason)
{
- unsigned int u = atomic_inc_return(&server->usage);
+ unsigned int u = atomic_inc_return(&server->ref);
+
+ trace_afs_server(server, u, atomic_read(&server->active), reason);
+ return server;
+}
+
+/*
+ * Try to get a reference on a server object.
+ */
+static struct afs_server *afs_maybe_use_server(struct afs_server *server,
+ enum afs_server_trace reason)
+{
+ unsigned int r = atomic_fetch_add_unless(&server->ref, 1, 0);
+ unsigned int a;
+
+ if (r == 0)
+ return NULL;
+
+ a = atomic_inc_return(&server->active);
+ trace_afs_server(server, r, a, reason);
+ return server;
+}
+
+/*
+ * Get an active count on a server object.
+ */
+struct afs_server *afs_use_server(struct afs_server *server, enum afs_server_trace reason)
+{
+ unsigned int r = atomic_inc_return(&server->ref);
+ unsigned int a = atomic_inc_return(&server->active);

- trace_afs_server(server, u, reason);
+ trace_afs_server(server, r, a, reason);
return server;
}

@@ -345,28 +378,56 @@ void afs_put_server(struct afs_net *net, struct afs_server *server,
if (!server)
return;

- server->put_time = ktime_get_real_seconds();
-
- usage = atomic_dec_return(&server->usage);
+ usage = atomic_dec_return(&server->ref);
+ trace_afs_server(server, usage, atomic_read(&server->active), reason);
+ if (unlikely(usage == 0))
+ __afs_put_server(net, server);
+}

- trace_afs_server(server, usage, reason);
+/*
+ * Drop an active count on a server object without updating the last-unused
+ * time.
+ */
+void afs_unuse_server_notime(struct afs_net *net, struct afs_server *server,
+ enum afs_server_trace reason)
+{
+ if (server) {
+ unsigned int active = atomic_dec_return(&server->active);

- if (likely(usage > 0))
- return;
+ if (active == 0)
+ afs_set_server_timer(net, afs_server_gc_delay);
+ afs_put_server(net, server, reason);
+ }
+}

- afs_set_server_timer(net, afs_server_gc_delay);
+/*
+ * Drop an active count on a server object.
+ */
+void afs_unuse_server(struct afs_net *net, struct afs_server *server,
+ enum afs_server_trace reason)
+{
+ if (server) {
+ server->unuse_time = ktime_get_real_seconds();
+ afs_unuse_server_notime(net, server, reason);
+ }
}

static void afs_server_rcu(struct rcu_head *rcu)
{
struct afs_server *server = container_of(rcu, struct afs_server, rcu);

- trace_afs_server(server, atomic_read(&server->usage),
- afs_server_trace_free);
+ trace_afs_server(server, atomic_read(&server->ref),
+ atomic_read(&server->active), afs_server_trace_free);
afs_put_addrlist(rcu_access_pointer(server->addresses));
kfree(server);
}

+static void __afs_put_server(struct afs_net *net, struct afs_server *server)
+{
+ call_rcu(&server->rcu, afs_server_rcu);
+ afs_dec_servers_outstanding(net);
+}
+
/*
* destroy a dead server
*/
@@ -379,19 +440,10 @@ static void afs_destroy_server(struct afs_net *net, struct afs_server *server)
.error = 0,
};

- trace_afs_server(server, atomic_read(&server->usage),
- afs_server_trace_give_up_cb);
-
if (test_bit(AFS_SERVER_FL_MAY_HAVE_CB, &server->flags))
afs_fs_give_up_all_callbacks(net, server, &ac, NULL);

- wait_var_event(&server->probe_outstanding,
- atomic_read(&server->probe_outstanding) == 0);
-
- trace_afs_server(server, atomic_read(&server->usage),
- afs_server_trace_destroy);
- call_rcu(&server->rcu, afs_server_rcu);
- afs_dec_servers_outstanding(net);
+ afs_put_server(net, server, afs_server_trace_destroy);
}

/*
@@ -400,31 +452,28 @@ static void afs_destroy_server(struct afs_net *net, struct afs_server *server)
static void afs_gc_servers(struct afs_net *net, struct afs_server *gc_list)
{
struct afs_server *server;
- bool deleted;
- int usage;
+ int active;

while ((server = gc_list)) {
gc_list = server->gc_next;

write_seqlock(&net->fs_lock);
- usage = 1;
- deleted = atomic_try_cmpxchg(&server->usage, &usage, 0);
- trace_afs_server(server, usage, afs_server_trace_gc);
- if (deleted) {
+
+ active = atomic_read(&server->active);
+ if (active == 0) {
+ trace_afs_server(server, atomic_read(&server->ref),
+ active, afs_server_trace_gc);
rb_erase(&server->uuid_rb, &net->fs_servers);
hlist_del_rcu(&server->proc_link);
- }
- write_sequnlock(&net->fs_lock);
-
- if (deleted) {
- write_seqlock(&net->fs_addr_lock);
if (!hlist_unhashed(&server->addr4_link))
hlist_del_rcu(&server->addr4_link);
if (!hlist_unhashed(&server->addr6_link))
hlist_del_rcu(&server->addr6_link);
- write_sequnlock(&net->fs_addr_lock);
- afs_destroy_server(net, server);
}
+ write_sequnlock(&net->fs_lock);
+
+ if (active == 0)
+ afs_destroy_server(net, server);
}
}

@@ -453,15 +502,14 @@ void afs_manage_servers(struct work_struct *work)
for (cursor = rb_first(&net->fs_servers); cursor; cursor = rb_next(cursor)) {
struct afs_server *server =
rb_entry(cursor, struct afs_server, uuid_rb);
- int usage = atomic_read(&server->usage);
+ int active = atomic_read(&server->active);

- _debug("manage %pU %u", &server->uuid, usage);
+ _debug("manage %pU %u", &server->uuid, active);

- ASSERTCMP(usage, >=, 1);
- ASSERTIFCMP(purging, usage, ==, 1);
+ ASSERTIFCMP(purging, active, ==, 0);

- if (usage == 1) {
- time64_t expire_at = server->put_time;
+ if (active == 0) {
+ time64_t expire_at = server->unuse_time;

if (!test_bit(AFS_SERVER_FL_VL_FAIL, &server->flags) &&
!test_bit(AFS_SERVER_FL_NOT_FOUND, &server->flags))
@@ -532,7 +580,8 @@ static noinline bool afs_update_server_record(struct afs_fs_cursor *fc, struct a

_enter("");

- trace_afs_server(server, atomic_read(&server->usage), afs_server_trace_update);
+ trace_afs_server(server, atomic_read(&server->ref), atomic_read(&server->active),
+ afs_server_trace_update);

alist = afs_vl_lookup_addrs(fc->vnode->volume->cell, fc->key,
&server->uuid);
diff --git a/fs/afs/server_list.c b/fs/afs/server_list.c
index f567732df5cc..b77e50f62459 100644
--- a/fs/afs/server_list.c
+++ b/fs/afs/server_list.c
@@ -16,8 +16,8 @@ void afs_put_serverlist(struct afs_net *net, struct afs_server_list *slist)
if (slist && refcount_dec_and_test(&slist->usage)) {
for (i = 0; i < slist->nr_servers; i++) {
afs_put_cb_interest(net, slist->servers[i].cb_interest);
- afs_put_server(net, slist->servers[i].server,
- afs_server_trace_put_slist);
+ afs_unuse_server(net, slist->servers[i].server,
+ afs_server_trace_put_slist);
}
kfree(slist);
}
diff --git a/include/trace/events/afs.h b/include/trace/events/afs.h
index c612cabbc378..f9691f69b2d6 100644
--- a/include/trace/events/afs.h
+++ b/include/trace/events/afs.h
@@ -33,6 +33,7 @@ enum afs_server_trace {
afs_server_trace_destroy,
afs_server_trace_free,
afs_server_trace_gc,
+ afs_server_trace_get_by_addr,
afs_server_trace_get_by_uuid,
afs_server_trace_get_caps,
afs_server_trace_get_install,
@@ -241,6 +242,7 @@ enum afs_cb_break_reason {
EM(afs_server_trace_destroy, "DESTROY ") \
EM(afs_server_trace_free, "FREE ") \
EM(afs_server_trace_gc, "GC ") \
+ EM(afs_server_trace_get_by_addr, "GET addr ") \
EM(afs_server_trace_get_by_uuid, "GET uuid ") \
EM(afs_server_trace_get_caps, "GET caps ") \
EM(afs_server_trace_get_install, "GET inst ") \
@@ -1271,26 +1273,30 @@ TRACE_EVENT(afs_cb_miss,
);

TRACE_EVENT(afs_server,
- TP_PROTO(struct afs_server *server, int usage, enum afs_server_trace reason),
+ TP_PROTO(struct afs_server *server, int ref, int active,
+ enum afs_server_trace reason),

- TP_ARGS(server, usage, reason),
+ TP_ARGS(server, ref, active, reason),

TP_STRUCT__entry(
__field(unsigned int, server )
- __field(int, usage )
+ __field(int, ref )
+ __field(int, active )
__field(int, reason )
),

TP_fast_assign(
__entry->server = server->debug_id;
- __entry->usage = usage;
+ __entry->ref = ref;
+ __entry->active = active;
__entry->reason = reason;
),

- TP_printk("s=%08x %s u=%d",
+ TP_printk("s=%08x %s u=%d a=%d",
__entry->server,
__print_symbolic(__entry->reason, afs_server_traces),
- __entry->usage)
+ __entry->ref,
+ __entry->active)
);

#endif /* _TRACE_AFS_H */