afs: Split the usage count on struct afs_server

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>

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);
 	}

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;

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;

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 *);

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;

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);