From cbd37330bcd039587121a767280fc9fee597af6e Mon Sep 17 00:00:00 2001 From: Michal Schmidt 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. --- 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 daa2c84a..81b4f534 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 111167a8..6acc821e 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 5deb5696..6e7558e1 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; -- 2.39.5