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core: fix priority ordering in notify-handling

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Currently, we dispatch NOTIFY messages in a tight loop. Regardless how
much data is incoming, we always dispatch everything that is queued.
This, however, completely breaks priority event-handling of sd-event.
When dispatching one NOTIFY event, another completely different event
might fire, or might be queued by the NOTIFY handling. However, this
event will not get dispatched until all other further NOTIFY messages are
handled. Those might even arrive _after_ the other event fired, and as
such completely break priority ordering of sd-event (which several code
paths rely on).

Break this by never dispatching multiple messages. Just return after each
message that was read and let sd-event handle everything else.

(The patch looks scarier that it is. It basically just drops the for(;;)
 loop and re-indents the loop-content.)
This commit is contained in:
David Herrmann 2015-10-28 19:11:36 +01:00
parent df5b3e1840
commit b215b0ede1
1 changed files with 92 additions and 94 deletions
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34
src/core/manager.c
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@ -1509,20 +1509,9 @@ static void manager_invoke_notify_message(Manager *m, Unit *u, pid_t pid, char *
}
static int manager_dispatch_notify_fd(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
Manager *m = userdata;
ssize_t n;
int r;
assert(m);
assert(m->notify_fd == fd);
if (revents != EPOLLIN) {
log_warning("Got unexpected poll event for notify fd.");
return 0;
}
for (;;) {
_cleanup_fdset_free_ FDSet *fds = NULL;
Manager *m = userdata;
char buf[NOTIFY_BUFFER_MAX+1];
struct iovec iovec = {
.iov_base = buf,
@ -1539,17 +1528,27 @@ static int manager_dispatch_notify_fd(sd_event_source *source, int fd, uint32_t
.msg_control = &control,
.msg_controllen = sizeof(control),
};
struct cmsghdr *cmsg;
struct ucred *ucred = NULL;
bool found = false;
Unit *u1, *u2, *u3;
int *fd_array = NULL;
int r, *fd_array = NULL;
unsigned n_fds = 0;
ssize_t n;
assert(m);
assert(m->notify_fd == fd);
if (revents != EPOLLIN) {
log_warning("Got unexpected poll event for notify fd.");
return 0;
}
n = recvmsg(m->notify_fd, &msghdr, MSG_DONTWAIT|MSG_CMSG_CLOEXEC);
if (n < 0) {
if (errno == EAGAIN || errno == EINTR)
break;
return 0;
return -errno;
}
@ -1580,12 +1579,12 @@ static int manager_dispatch_notify_fd(sd_event_source *source, int fd, uint32_t
if (!ucred || ucred->pid <= 0) {
log_warning("Received notify message without valid credentials. Ignoring.");
continue;
return 0;
}
if ((size_t) n >= sizeof(buf)) {
log_warning("Received notify message exceeded maximum size. Ignoring.");
continue;
return 0;
}
buf[n] = 0;
@ -1615,7 +1614,6 @@ static int manager_dispatch_notify_fd(sd_event_source *source, int fd, uint32_t
if (fdset_size(fds) > 0)
log_warning("Got auxiliary fds with notification message, closing all.");
}
return 0;
}