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afs: Split the usage count on struct afs_server

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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@redhat.com>
This commit is contained in:
David Howells
2020-04-17 17:31:26 +01:00
parent 8100680592
commit 977e5f8ed0
9 changed files with 131 additions and 71 deletions
Download Patch File Download Diff File Expand all files Collapse all files

151
fs/afs/server.c
View File

@@ -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 @@ exists:
}
/*
* 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, reason);
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, 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->ref);
trace_afs_server(server, usage, atomic_read(&server->active), reason);
if (unlikely(usage == 0))
__afs_put_server(net, server);
}
usage = atomic_dec_return(&server->usage);
/*
* 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);
trace_afs_server(server, usage, reason);
if (active == 0)
afs_set_server_timer(net, afs_server_gc_delay);
afs_put_server(net, server, reason);
}
}
if (likely(usage > 0))
return;
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);