journald: never block when sending messages on NOTIFY_SOCKET socket

Otherwise we might run into deadlocks, when journald blocks on the
notify socket on PID 1, and PID 1 blocks on IPC to dbus-daemon and
dbus-daemon blocks on logging to journald. Break this cycle by making
sure that journald never ever blocks on PID 1.

Note that this change disables support for event loop watchdog support,
as these messages are sent in blocking style by sd-event. That should
not be a big loss though, as people reported frequent problems with the
watchdog hitting journald on excessively slow IO.

Fixes: #1505.

1 files changed, 9 insertions, 4 deletions

diff --git a/src/journal/journald-server.h b/src/journal/journald-server.h
index a2631c6017..170602ea16 100644
--- a/src/journal/journald-server.h
+++ b/src/journal/journald-server.h
@@ -26,9 +26,12 @@
 
 #include "sd-event.h"
 
+typedef struct Server Server;
+
 #include "hashmap.h"
 #include "journal-file.h"
 #include "journald-rate-limit.h"
+#include "journald-stream.h"
 #include "list.h"
 
 typedef enum Storage {
@@ -48,15 +51,14 @@ typedef enum SplitMode {
         _SPLIT_INVALID = -1
 } SplitMode;
 
-typedef struct StdoutStream StdoutStream;
-
-typedef struct Server {
+struct Server {
         int syslog_fd;
         int native_fd;
         int stdout_fd;
         int dev_kmsg_fd;
         int audit_fd;
         int hostname_fd;
+        int notify_fd;
 
         sd_event *event;
 
@@ -71,6 +73,7 @@ typedef struct Server {
         sd_event_source *sigterm_event_source;
         sd_event_source *sigint_event_source;
         sd_event_source *hostname_event_source;
+        sd_event_source *notify_event_source;
 
         JournalFile *runtime_journal;
         JournalFile *system_journal;
@@ -111,6 +114,7 @@ typedef struct Server {
         usec_t oldest_file_usec;
 
         LIST_HEAD(StdoutStream, stdout_streams);
+        LIST_HEAD(StdoutStream, stdout_streams_notify_queue);
         unsigned n_stdout_streams;
 
         char *tty_path;
@@ -132,6 +136,7 @@ typedef struct Server {
 
         struct udev *udev;
 
+        bool sent_notify_ready;
         bool sync_scheduled;
 
         char machine_id_field[sizeof("_MACHINE_ID=") + 32];
@@ -140,7 +145,7 @@ typedef struct Server {
 
         /* Cached cgroup root, so that we don't have to query that all the time */
         char *cgroup_root;
-} Server;
+};
 
 #define SERVER_MACHINE_ID(s) ((s)->machine_id_field + strlen("_MACHINE_ID="))