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core: Avoid race when starting dbus services

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In high load scenarios it is possible for services to be started
before the NameOwnerChanged signal is properly installed.

Emulate a callback by also queuing a GetNameOwner when the match is
installed.

Fixes: #12956
This commit is contained in:
Mattias Jernberg 2019-07-11 18:13:46 +02:00 committed by Lennart Poettering
parent f364a17dd1
commit a5a8776ae5
4 changed files with 63 additions and 13 deletions
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4
src/core/dbus.c
View File

@ -784,7 +784,7 @@ static int manager_dispatch_sync_bus_names(sd_event_source *es, void *userdata)
* changed, so synthesize a name owner changed signal. */
if (!streq_ptr(unique, s->bus_name_owner))
UNIT_VTABLE(u)->bus_name_owner_change(u, name, s->bus_name_owner, unique);
UNIT_VTABLE(u)->bus_name_owner_change(u, s->bus_name_owner, unique);
} else {
/* So, the name we're watching is not on the bus.
* This either means it simply hasn't appeared yet,
@ -793,7 +793,7 @@ static int manager_dispatch_sync_bus_names(sd_event_source *es, void *userdata)
* and synthesize a name loss signal in this case. */
if (s->bus_name_owner)
UNIT_VTABLE(u)->bus_name_owner_change(u, name, s->bus_name_owner, NULL);
UNIT_VTABLE(u)->bus_name_owner_change(u, s->bus_name_owner, NULL);
}
}

13
src/core/service.c
View File

@ -4067,7 +4067,6 @@ static int service_get_timeout(Unit *u, usec_t *timeout) {
static void service_bus_name_owner_change(
Unit *u,
const char *name,
const char *old_owner,
const char *new_owner) {
@ -4075,17 +4074,15 @@ static void service_bus_name_owner_change(
int r;
assert(s);
assert(name);
assert(streq(s->bus_name, name));
assert(old_owner || new_owner);
if (old_owner && new_owner)
log_unit_debug(u, "D-Bus name %s changed owner from %s to %s", name, old_owner, new_owner);
log_unit_debug(u, "D-Bus name %s changed owner from %s to %s", s->bus_name, old_owner, new_owner);
else if (old_owner)
log_unit_debug(u, "D-Bus name %s no longer registered by %s", name, old_owner);
log_unit_debug(u, "D-Bus name %s no longer registered by %s", s->bus_name, old_owner);
else
log_unit_debug(u, "D-Bus name %s now registered by %s", name, new_owner);
log_unit_debug(u, "D-Bus name %s now registered by %s", s->bus_name, new_owner);
s->bus_name_good = !!new_owner;
@ -4118,11 +4115,11 @@ static void service_bus_name_owner_change(
/* Try to acquire PID from bus service */
r = sd_bus_get_name_creds(u->manager->api_bus, name, SD_BUS_CREDS_PID, &creds);
r = sd_bus_get_name_creds(u->manager->api_bus, s->bus_name, SD_BUS_CREDS_PID, &creds);
if (r >= 0)
r = sd_bus_creds_get_pid(creds, &pid);
if (r >= 0) {
log_unit_debug(u, "D-Bus name %s is now owned by process " PID_FMT, name, pid);
log_unit_debug(u, "D-Bus name %s is now owned by process " PID_FMT, s->bus_name, pid);
service_set_main_pid(s, pid);
unit_watch_pid(UNIT(s), pid, false);

56
src/core/unit.c
View File

@ -3242,7 +3242,46 @@ static int signal_name_owner_changed(sd_bus_message *message, void *userdata, sd
new_owner = empty_to_null(new_owner);
if (UNIT_VTABLE(u)->bus_name_owner_change)
UNIT_VTABLE(u)->bus_name_owner_change(u, name, old_owner, new_owner);
UNIT_VTABLE(u)->bus_name_owner_change(u, old_owner, new_owner);
return 0;
}
static int get_name_owner_handler(sd_bus_message *message, void *userdata, sd_bus_error *error) {
const sd_bus_error *e;
const char *new_owner;
Unit *u = userdata;
int r;
assert(message);
assert(u);
u->get_name_owner_slot = sd_bus_slot_unref(u->get_name_owner_slot);
if (sd_bus_error_is_set(error)) {
log_error("Failed to get name owner from bus: %s", error->message);
return 0;
}
e = sd_bus_message_get_error(message);
if (sd_bus_error_has_name(e, "org.freedesktop.DBus.Error.NameHasNoOwner"))
return 0;
if (e) {
log_error("Unexpected error response from GetNameOwner: %s", e->message);
return 0;
}
r = sd_bus_message_read(message, "s", &new_owner);
if (r < 0) {
bus_log_parse_error(r);
return 0;
}
new_owner = empty_to_null(new_owner);
if (UNIT_VTABLE(u)->bus_name_owner_change)
UNIT_VTABLE(u)->bus_name_owner_change(u, NULL, new_owner);
return 0;
}
@ -3264,7 +3303,19 @@ int unit_install_bus_match(Unit *u, sd_bus *bus, const char *name) {
"member='NameOwnerChanged',"
"arg0='", name, "'");
return sd_bus_add_match_async(bus, &u->match_bus_slot, match, signal_name_owner_changed, NULL, u);
int r = sd_bus_add_match_async(bus, &u->match_bus_slot, match, signal_name_owner_changed, NULL, u);
if (r < 0)
return r;
return sd_bus_call_method_async(bus,
&u->get_name_owner_slot,
"org.freedesktop.DBus",
"/org/freedesktop/DBus",
"org.freedesktop.DBus",
"GetNameOwner",
get_name_owner_handler,
u,
"s", name);
}
int unit_watch_bus_name(Unit *u, const char *name) {
@ -3299,6 +3350,7 @@ void unit_unwatch_bus_name(Unit *u, const char *name) {
(void) hashmap_remove_value(u->manager->watch_bus, name, u);
u->match_bus_slot = sd_bus_slot_unref(u->match_bus_slot);
u->get_name_owner_slot = sd_bus_slot_unref(u->get_name_owner_slot);
}
bool unit_can_serialize(Unit *u) {

3
src/core/unit.h
View File

@ -146,6 +146,7 @@ typedef struct Unit {
/* The slot used for watching NameOwnerChanged signals */
sd_bus_slot *match_bus_slot;
sd_bus_slot *get_name_owner_slot;
/* References to this unit from clients */
sd_bus_track *bus_track;
@ -528,7 +529,7 @@ typedef struct UnitVTable {
void (*notify_message)(Unit *u, const struct ucred *ucred, char **tags, FDSet *fds);
/* Called whenever a name this Unit registered for comes or goes away. */
void (*bus_name_owner_change)(Unit *u, const char *name, const char *old_owner, const char *new_owner);
void (*bus_name_owner_change)(Unit *u, const char *old_owner, const char *new_owner);
/* Called for each property that is being set */
int (*bus_set_property)(Unit *u, const char *name, sd_bus_message *message, UnitWriteFlags flags, sd_bus_error *error);