From 6e1da63130bb563b5cce89c2a7d66e98e79c5ec4 Mon Sep 17 00:00:00 2001
From: Michal Schmidt <mschmidt@redhat.com>
Date: Sun, 18 Dec 2011 14:58:10 +0100
Subject: [PATCH] dbus: register to DBus asynchronously
Chen Jie observed and analyzed a deadlock. Assuming systemd-kmsg-syslogd
is already stopped, but rsyslogd is not started yet:
1. systemd makes a synchronous call to dbus-daemon.
2. dbus-daemon wants to write something to syslog.
3. syslog needs to be started by systemd.
... but cannot be, because systemd is waiting in 1.
Solve this by avoiding synchronous D-Bus calls. I had to write an async
bus registration call. Interestingly, D-Bus authors anticipated this, in
documentation to dbus_bus_set_unique_name():
> The only reason to use this function is to re-implement the equivalent
> of dbus_bus_register() yourself. One (probably unusual) reason to do
> that might be to do the bus registration call asynchronously instead
> of synchronously.
Lennart's comments from IRC:
> though I think this doesn't fix the problem in its entirety
> simply because dbus_connection_open_private() itself is still synchronous
> i.e. the connect() call behind it is not async
> I think I listed that issue actually on some D-Bus todo list
> i.e. to make dbus_connection_get() fully async
> but that's going to be hard
> so your patch looks good
So it may not be perfect, but it's clearly an improvement.
I did not manage to reproduce the original deadlock with the patch.
(cherry picked from commit cbd37330bcd039587121a767280fc9fee597af6e)
---
src/dbus.c | 378 +++++++++++++++++++++++++++++++++++++++------------------
src/manager.c | 2 +-
src/manager.h | 1 +
3 files changed, 262 insertions(+), 119 deletions(-)
diff --git a/src/dbus.c b/src/dbus.c
index daa2c84..81b4f53 100644
--- a/src/dbus.c
+++ b/src/dbus.c
@@ -48,6 +48,11 @@
#define CONNECTIONS_MAX 52
+/* Well-known address (http://dbus.freedesktop.org/doc/dbus-specification.html#message-bus-types) */
+#define DBUS_SYSTEM_BUS_DEFAULT_ADDRESS "unix:path=/var/run/dbus/system_bus_socket"
+/* Only used as a fallback */
+#define DBUS_SESSION_BUS_DEFAULT_ADDRESS "autolaunch:"
+
static const char bus_properties_interface[] = BUS_PROPERTIES_INTERFACE;
static const char bus_introspectable_interface[] = BUS_INTROSPECTABLE_INTERFACE;
@@ -767,37 +772,19 @@ static void bus_new_connection(
dbus_connection_ref(new_connection);
}
-static int bus_init_system(Manager *m) {
- DBusError error;
- int r;
-
- assert(m);
-
- dbus_error_init(&error);
-
- if (m->system_bus)
- return 0;
-
- if (m->running_as == MANAGER_SYSTEM && m->api_bus)
- m->system_bus = m->api_bus;
- else {
- if (!(m->system_bus = dbus_bus_get_private(DBUS_BUS_SYSTEM, &error))) {
- log_debug("Failed to get system D-Bus connection, retrying later: %s", bus_error_message(&error));
- r = 0;
- goto fail;
- }
-
- if ((r = bus_setup_loop(m, m->system_bus)) < 0)
- goto fail;
- }
+static int init_registered_system_bus(Manager *m) {
+ char *id;
if (!dbus_connection_add_filter(m->system_bus, system_bus_message_filter, m, NULL)) {
log_error("Not enough memory");
- r = -ENOMEM;
- goto fail;
+ return -ENOMEM;
}
if (m->running_as != MANAGER_SYSTEM) {
+ DBusError error;
+
+ dbus_error_init(&error);
+
dbus_bus_add_match(m->system_bus,
"type='signal',"
"interface='org.freedesktop.systemd1.Agent',"
@@ -807,59 +794,28 @@ static int bus_init_system(Manager *m) {
if (dbus_error_is_set(&error)) {
log_error("Failed to register match: %s", bus_error_message(&error));
- r = -EIO;
- goto fail;
+ dbus_error_free(&error);
+ return -1;
}
}
- if (m->api_bus != m->system_bus) {
- char *id;
- log_debug("Successfully connected to system D-Bus bus %s as %s",
- strnull((id = dbus_connection_get_server_id(m->system_bus))),
- strnull(dbus_bus_get_unique_name(m->system_bus)));
- dbus_free(id);
- }
+ log_debug("Successfully connected to system D-Bus bus %s as %s",
+ strnull((id = dbus_connection_get_server_id(m->system_bus))),
+ strnull(dbus_bus_get_unique_name(m->system_bus)));
+ dbus_free(id);
return 0;
-
-fail:
- bus_done_system(m);
- dbus_error_free(&error);
-
- return r;
}
-static int bus_init_api(Manager *m) {
- DBusError error;
+static int init_registered_api_bus(Manager *m) {
int r;
- assert(m);
-
- dbus_error_init(&error);
-
- if (m->api_bus)
- return 0;
-
- if (m->running_as == MANAGER_SYSTEM && m->system_bus)
- m->api_bus = m->system_bus;
- else {
- if (!(m->api_bus = dbus_bus_get_private(m->running_as == MANAGER_USER ? DBUS_BUS_SESSION : DBUS_BUS_SYSTEM, &error))) {
- log_debug("Failed to get API D-Bus connection, retrying later: %s", bus_error_message(&error));
- r = 0;
- goto fail;
- }
-
- if ((r = bus_setup_loop(m, m->api_bus)) < 0)
- goto fail;
- }
-
if (!dbus_connection_register_object_path(m->api_bus, "/org/freedesktop/systemd1", &bus_manager_vtable, m) ||
!dbus_connection_register_fallback(m->api_bus, "/org/freedesktop/systemd1/unit", &bus_unit_vtable, m) ||
!dbus_connection_register_fallback(m->api_bus, "/org/freedesktop/systemd1/job", &bus_job_vtable, m) ||
!dbus_connection_add_filter(m->api_bus, api_bus_message_filter, m, NULL)) {
log_error("Not enough memory");
- r = -ENOMEM;
- goto fail;
+ return -ENOMEM;
}
/* Get NameOwnerChange messages */
@@ -869,13 +825,7 @@ static int bus_init_api(Manager *m) {
"interface='"DBUS_INTERFACE_DBUS"',"
"member='NameOwnerChanged',"
"path='"DBUS_PATH_DBUS"'",
- &error);
-
- if (dbus_error_is_set(&error)) {
- log_error("Failed to register match: %s", bus_error_message(&error));
- r = -EIO;
- goto fail;
- }
+ NULL);
/* Get activation requests */
dbus_bus_add_match(m->api_bus,
@@ -884,33 +834,225 @@ static int bus_init_api(Manager *m) {
"interface='org.freedesktop.systemd1.Activator',"
"member='ActivationRequest',"
"path='"DBUS_PATH_DBUS"'",
- &error);
-
- if (dbus_error_is_set(&error)) {
- log_error("Failed to register match: %s", bus_error_message(&error));
- r = -EIO;
- goto fail;
- }
+ NULL);
- if ((r = request_name(m)) < 0)
- goto fail;
+ r = request_name(m);
+ if (r < 0)
+ return r;
- if ((r = query_name_list(m)) < 0)
- goto fail;
+ r = query_name_list(m);
+ if (r < 0)
+ return r;
- if (m->api_bus != m->system_bus) {
+ if (m->running_as == MANAGER_USER) {
char *id;
log_debug("Successfully connected to API D-Bus bus %s as %s",
strnull((id = dbus_connection_get_server_id(m->api_bus))),
strnull(dbus_bus_get_unique_name(m->api_bus)));
dbus_free(id);
+ } else
+ log_debug("Successfully initialized API on the system bus");
+
+ return 0;
+}
+
+static void bus_register_cb(DBusPendingCall *pending, void *userdata) {
+ Manager *m = userdata;
+ DBusConnection **conn;
+ DBusMessage *reply;
+ DBusError error;
+ const char *name;
+ int r = 0;
+
+ dbus_error_init(&error);
+
+ conn = dbus_pending_call_get_data(pending, m->conn_data_slot);
+ assert(conn == &m->system_bus || conn == &m->api_bus);
+
+ reply = dbus_pending_call_steal_reply(pending);
+
+ switch (dbus_message_get_type(reply)) {
+ case DBUS_MESSAGE_TYPE_ERROR:
+ assert_se(dbus_set_error_from_message(&error, reply));
+ log_warning("Failed to register to bus: %s", bus_error_message(&error));
+ r = -1;
+ break;
+ case DBUS_MESSAGE_TYPE_METHOD_RETURN:
+ if (!dbus_message_get_args(reply, &error,
+ DBUS_TYPE_STRING, &name,
+ DBUS_TYPE_INVALID)) {
+ log_error("Failed to parse Hello reply: %s", bus_error_message(&error));
+ r = -1;
+ break;
+ }
+
+ log_debug("Received name %s in reply to Hello", name);
+ if (!dbus_bus_set_unique_name(*conn, name)) {
+ log_error("Failed to set unique name");
+ r = -1;
+ break;
+ }
+
+ if (conn == &m->system_bus) {
+ r = init_registered_system_bus(m);
+ if (r == 0 && m->running_as == MANAGER_SYSTEM)
+ r = init_registered_api_bus(m);
+ } else
+ r = init_registered_api_bus(m);
+
+ break;
+ default:
+ assert_not_reached("Invalid reply message");
+ }
+
+ dbus_message_unref(reply);
+ dbus_error_free(&error);
+
+ if (r < 0) {
+ if (conn == &m->system_bus) {
+ log_debug("Failed setting up the system bus");
+ bus_done_system(m);
+ } else {
+ log_debug("Failed setting up the API bus");
+ bus_done_api(m);
+ }
+ }
+}
+
+static int manager_bus_async_register(Manager *m, DBusConnection **conn) {
+ DBusMessage *message = NULL;
+ DBusPendingCall *pending = NULL;
+
+ message = dbus_message_new_method_call(DBUS_SERVICE_DBUS,
+ DBUS_PATH_DBUS,
+ DBUS_INTERFACE_DBUS,
+ "Hello");
+ if (!message)
+ goto oom;
+
+ if (!dbus_connection_send_with_reply(*conn, message, &pending, -1))
+ goto oom;
+
+ if (!dbus_pending_call_set_data(pending, m->conn_data_slot, conn, NULL))
+ goto oom;
+
+ if (!dbus_pending_call_set_notify(pending, bus_register_cb, m, NULL))
+ goto oom;
+
+ dbus_message_unref(message);
+ dbus_pending_call_unref(pending);
+
+ return 0;
+oom:
+ if (pending) {
+ dbus_pending_call_cancel(pending);
+ dbus_pending_call_unref(pending);
+ }
+
+ if (message)
+ dbus_message_unref(message);
+
+ return -ENOMEM;
+}
+
+static DBusConnection* manager_bus_connect_private(Manager *m, DBusBusType type) {
+ const char *address;
+ DBusConnection *connection;
+ DBusError error;
+
+ switch (type) {
+ case DBUS_BUS_SYSTEM:
+ address = getenv("DBUS_SYSTEM_BUS_ADDRESS");
+ if (!address || !address[0])
+ address = DBUS_SYSTEM_BUS_DEFAULT_ADDRESS;
+ break;
+ case DBUS_BUS_SESSION:
+ address = getenv("DBUS_SESSION_BUS_ADDRESS");
+ if (!address || !address[0])
+ address = DBUS_SESSION_BUS_DEFAULT_ADDRESS;
+ break;
+ default:
+ assert_not_reached("Invalid bus type");
+ }
+
+ dbus_error_init(&error);
+
+ connection = dbus_connection_open_private(address, &error);
+ if (!connection) {
+ log_warning("Failed to open private bus connection: %s", bus_error_message(&error));
+ goto fail;
+ }
+
+ return connection;
+fail:
+ if (connection)
+ dbus_connection_close(connection);
+ dbus_error_free(&error);
+ return NULL;
+}
+
+static int bus_init_system(Manager *m) {
+ int r;
+
+ if (m->system_bus)
+ return 0;
+
+ m->system_bus = manager_bus_connect_private(m, DBUS_BUS_SYSTEM);
+ if (!m->system_bus) {
+ log_debug("Failed to connect to system D-Bus, retrying later");
+ r = 0;
+ goto fail;
}
+ r = bus_setup_loop(m, m->system_bus);
+ if (r < 0)
+ goto fail;
+
+ r = manager_bus_async_register(m, &m->system_bus);
+ if (r < 0)
+ goto fail;
+
return 0;
+fail:
+ bus_done_system(m);
+
+ return r;
+}
+
+static int bus_init_api(Manager *m) {
+ int r;
+
+ if (m->api_bus)
+ return 0;
+
+ if (m->running_as == MANAGER_SYSTEM) {
+ m->api_bus = m->system_bus;
+ /* In this mode there is no distinct connection to the API bus,
+ * the API is published on the system bus.
+ * bus_register_cb() is aware of that and will init the API
+ * when the system bus gets registered.
+ * No need to setup anything here. */
+ return 0;
+ }
+
+ m->api_bus = manager_bus_connect_private(m, DBUS_BUS_SESSION);
+ if (!m->api_bus) {
+ log_debug("Failed to connect to API D-Bus, retrying later");
+ r = 0;
+ goto fail;
+ }
+
+ r = bus_setup_loop(m, m->api_bus);
+ if (r < 0)
+ goto fail;
+ r = manager_bus_async_register(m, &m->api_bus);
+ if (r < 0)
+ goto fail;
+
+ return 0;
fail:
bus_done_api(m);
- dbus_error_free(&error);
return r;
}
@@ -989,22 +1131,20 @@ int bus_init(Manager *m, bool try_bus_connect) {
int r;
if (set_ensure_allocated(&m->bus_connections, trivial_hash_func, trivial_compare_func) < 0 ||
- set_ensure_allocated(&m->bus_connections_for_dispatch, trivial_hash_func, trivial_compare_func) < 0) {
- log_error("Not enough memory");
- return -ENOMEM;
- }
+ set_ensure_allocated(&m->bus_connections_for_dispatch, trivial_hash_func, trivial_compare_func) < 0)
+ goto oom;
if (m->name_data_slot < 0)
- if (!dbus_pending_call_allocate_data_slot(&m->name_data_slot)) {
- log_error("Not enough memory");
- return -ENOMEM;
- }
+ if (!dbus_pending_call_allocate_data_slot(&m->name_data_slot))
+ goto oom;
+
+ if (m->conn_data_slot < 0)
+ if (!dbus_pending_call_allocate_data_slot(&m->conn_data_slot))
+ goto oom;
if (m->subscribed_data_slot < 0)
- if (!dbus_connection_allocate_data_slot(&m->subscribed_data_slot)) {
- log_error("Not enough memory");
- return -ENOMEM;
- }
+ if (!dbus_connection_allocate_data_slot(&m->subscribed_data_slot))
+ goto oom;
if (try_bus_connect) {
if ((r = bus_init_system(m)) < 0 ||
@@ -1016,6 +1156,9 @@ int bus_init(Manager *m, bool try_bus_connect) {
return r;
return 0;
+oom:
+ log_error("Not enough memory");
+ return -ENOMEM;
}
static void shutdown_connection(Manager *m, DBusConnection *c) {
@@ -1059,42 +1202,38 @@ static void shutdown_connection(Manager *m, DBusConnection *c) {
}
static void bus_done_api(Manager *m) {
- assert(m);
-
- if (m->api_bus) {
- if (m->system_bus == m->api_bus)
- m->system_bus = NULL;
+ if (!m->api_bus)
+ return;
+ if (m->running_as == MANAGER_USER)
shutdown_connection(m, m->api_bus);
- m->api_bus = NULL;
- }
+ m->api_bus = NULL;
- if (m->queued_message) {
- dbus_message_unref(m->queued_message);
- m->queued_message = NULL;
- }
+ if (m->queued_message) {
+ dbus_message_unref(m->queued_message);
+ m->queued_message = NULL;
+ }
}
static void bus_done_system(Manager *m) {
- assert(m);
+ if (!m->system_bus)
+ return;
- if (m->system_bus == m->api_bus)
+ if (m->running_as == MANAGER_SYSTEM)
bus_done_api(m);
- if (m->system_bus) {
- shutdown_connection(m, m->system_bus);
- m->system_bus = NULL;
- }
+ shutdown_connection(m, m->system_bus);
+ m->system_bus = NULL;
}
static void bus_done_private(Manager *m) {
+ if (!m->private_bus)
+ return;
- if (m->private_bus) {
- dbus_server_disconnect(m->private_bus);
- dbus_server_unref(m->private_bus);
- m->private_bus = NULL;
- }
+ dbus_server_disconnect(m->private_bus);
+ dbus_server_unref(m->private_bus);
+ m->private_bus = NULL;
}
void bus_done(Manager *m) {
@@ -1116,6 +1255,9 @@ void bus_done(Manager *m) {
if (m->name_data_slot >= 0)
dbus_pending_call_free_data_slot(&m->name_data_slot);
+ if (m->conn_data_slot >= 0)
+ dbus_pending_call_free_data_slot(&m->conn_data_slot);
+
if (m->subscribed_data_slot >= 0)
dbus_connection_free_data_slot(&m->subscribed_data_slot);
}
diff --git a/src/manager.c b/src/manager.c
index 111167a..6acc821 100644
--- a/src/manager.c
+++ b/src/manager.c
@@ -231,7 +231,7 @@ int manager_new(ManagerRunningAs running_as, Manager **_m) {
dual_timestamp_get(&m->startup_timestamp);
m->running_as = running_as;
- m->name_data_slot = m->subscribed_data_slot = -1;
+ m->name_data_slot = m->conn_data_slot = m->subscribed_data_slot = -1;
m->exit_code = _MANAGER_EXIT_CODE_INVALID;
m->pin_cgroupfs_fd = -1;
diff --git a/src/manager.h b/src/manager.h
index 5deb569..6e7558e 100644
--- a/src/manager.h
+++ b/src/manager.h
@@ -179,6 +179,7 @@ struct Manager {
Hashmap *watch_bus; /* D-Bus names => Unit object n:1 */
int32_t name_data_slot;
+ int32_t conn_data_slot;
int32_t subscribed_data_slot;
uint32_t current_job_id;