1
1
mirror of https://github.com/systemd/systemd-stable.git synced 2024-12-23 17:34:00 +03:00

sd-event: re-check new epoll events when a child event is queued

Previously, when a process outputs something and exit just after
epoll_wait() but before process_child(), then the IO event is ignored
even if the IO event has higher priority. See #18190.

This can be solved by checking epoll event again after process_child().

However, there exists a possibility that another process outputs and
exits just after process_child() but before the second epoll_wait().
When the IO event has lower priority than the child event, still IO
event is processed.

So, this makes new epoll events and child events are checked in a loop
until no new event is detected. To prevent an infinite loop, the number
of maximum trial is set to 10.

Fixes #18190.
This commit is contained in:
Yu Watanabe 2021-03-08 15:39:53 +09:00
parent 7fe11e84c2
commit 84e998c112

View File

@ -1039,7 +1039,7 @@ static int source_set_pending(sd_event_source *s, bool b) {
}
}
return 0;
return 1;
}
static sd_event_source *source_new(sd_event *e, bool floating, EventSourceType type) {
@ -3116,12 +3116,19 @@ static int process_timer(
return 0;
}
static int process_child(sd_event *e) {
static int process_child(sd_event *e, int64_t threshold, int64_t *ret_min_priority) {
int64_t min_priority = threshold;
bool something_new = false;
sd_event_source *s;
int r;
assert(e);
if (!e->need_process_child) {
*ret_min_priority = min_priority;
return 0;
}
e->need_process_child = false;
/*
@ -3145,6 +3152,9 @@ static int process_child(sd_event *e) {
HASHMAP_FOREACH(s, e->child_sources) {
assert(s->type == SOURCE_CHILD);
if (s->priority > threshold)
continue;
if (s->pending)
continue;
@ -3181,10 +3191,15 @@ static int process_child(sd_event *e) {
r = source_set_pending(s, true);
if (r < 0)
return r;
if (r > 0) {
something_new = true;
min_priority = MIN(min_priority, s->priority);
}
}
}
return 0;
*ret_min_priority = min_priority;
return something_new;
}
static int process_pidfd(sd_event *e, sd_event_source *s, uint32_t revents) {
@ -3214,13 +3229,13 @@ static int process_pidfd(sd_event *e, sd_event_source *s, uint32_t revents) {
return source_set_pending(s, true);
}
static int process_signal(sd_event *e, struct signal_data *d, uint32_t events) {
bool read_one = false;
static int process_signal(sd_event *e, struct signal_data *d, uint32_t events, int64_t *min_priority) {
int r;
assert(e);
assert(d);
assert_return(events == EPOLLIN, -EIO);
assert(min_priority);
/* If there's a signal queued on this priority and SIGCHLD is
on this priority too, then make sure to recheck the
@ -3246,7 +3261,7 @@ static int process_signal(sd_event *e, struct signal_data *d, uint32_t events) {
n = read(d->fd, &si, sizeof(si));
if (n < 0) {
if (IN_SET(errno, EAGAIN, EINTR))
return read_one;
return 0;
return -errno;
}
@ -3256,8 +3271,6 @@ static int process_signal(sd_event *e, struct signal_data *d, uint32_t events) {
assert(SIGNAL_VALID(si.ssi_signo));
read_one = true;
if (e->signal_sources)
s = e->signal_sources[si.ssi_signo];
if (!s)
@ -3271,12 +3284,16 @@ static int process_signal(sd_event *e, struct signal_data *d, uint32_t events) {
r = source_set_pending(s, true);
if (r < 0)
return r;
if (r > 0 && *min_priority >= s->priority) {
*min_priority = s->priority;
return 1; /* an event source with smaller priority is queued. */
}
return 1;
return 0;
}
}
static int event_inotify_data_read(sd_event *e, struct inotify_data *d, uint32_t revents) {
static int event_inotify_data_read(sd_event *e, struct inotify_data *d, uint32_t revents, int64_t threshold) {
ssize_t n;
assert(e);
@ -3292,6 +3309,9 @@ static int event_inotify_data_read(sd_event *e, struct inotify_data *d, uint32_t
if (d->buffer_filled > 0)
return 0;
if (d->priority > threshold)
return 0;
n = read(d->fd, &d->buffer, sizeof(d->buffer));
if (n < 0) {
if (IN_SET(errno, EAGAIN, EINTR))
@ -3831,20 +3851,13 @@ static int epoll_wait_usec(
return r;
}
_public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
static int process_epoll(sd_event *e, usec_t timeout, int64_t threshold, int64_t *ret_min_priority) {
int64_t min_priority = threshold;
bool something_new = false;
size_t n_event_queue, m;
int r;
assert_return(e, -EINVAL);
assert_return(e = event_resolve(e), -ENOPKG);
assert_return(!event_pid_changed(e), -ECHILD);
assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
assert_return(e->state == SD_EVENT_ARMED, -EBUSY);
if (e->exit_requested) {
e->state = SD_EVENT_PENDING;
return 1;
}
assert(e);
n_event_queue = MAX(e->n_sources, 1u);
if (!GREEDY_REALLOC(e->event_queue, e->event_queue_allocated, n_event_queue))
@ -3856,12 +3869,8 @@ _public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
for (;;) {
r = epoll_wait_usec(e->epoll_fd, e->event_queue, e->event_queue_allocated, timeout);
if (r == -EINTR) {
e->state = SD_EVENT_PENDING;
return 1;
}
if (r < 0)
goto finish;
return r;
m = (size_t) r;
@ -3877,7 +3886,9 @@ _public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
timeout = 0;
}
triple_timestamp_get(&e->timestamp);
/* Set timestamp only when this is called first time. */
if (threshold == INT64_MAX)
triple_timestamp_get(&e->timestamp);
for (size_t i = 0; i < m; i++) {
@ -3893,6 +3904,11 @@ _public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
assert(s);
if (s->priority > threshold)
break;
min_priority = MIN(min_priority, s->priority);
switch (s->type) {
case SOURCE_IO:
@ -3920,19 +3936,75 @@ _public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
}
case WAKEUP_SIGNAL_DATA:
r = process_signal(e, e->event_queue[i].data.ptr, e->event_queue[i].events);
r = process_signal(e, e->event_queue[i].data.ptr, e->event_queue[i].events, &min_priority);
break;
case WAKEUP_INOTIFY_DATA:
r = event_inotify_data_read(e, e->event_queue[i].data.ptr, e->event_queue[i].events);
r = event_inotify_data_read(e, e->event_queue[i].data.ptr, e->event_queue[i].events, threshold);
break;
default:
assert_not_reached("Invalid wake-up pointer");
}
}
if (r < 0)
return r;
if (r > 0)
something_new = true;
}
*ret_min_priority = min_priority;
return something_new;
}
_public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
int r;
assert_return(e, -EINVAL);
assert_return(e = event_resolve(e), -ENOPKG);
assert_return(!event_pid_changed(e), -ECHILD);
assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
assert_return(e->state == SD_EVENT_ARMED, -EBUSY);
if (e->exit_requested) {
e->state = SD_EVENT_PENDING;
return 1;
}
for (int64_t threshold = INT64_MAX; ; threshold--) {
int64_t epoll_min_priority, child_min_priority;
/* There may be a possibility that new epoll (especially IO) and child events are
* triggered just after process_epoll() call but before process_child(), and the new IO
* events may have higher priority than the child events. To salvage these events,
* let's call epoll_wait() again, but accepts only events with higher priority than the
* previous. See issue https://github.com/systemd/systemd/issues/18190 and comments
* https://github.com/systemd/systemd/pull/18750#issuecomment-785801085
* https://github.com/systemd/systemd/pull/18922#issuecomment-792825226 */
r = process_epoll(e, timeout, threshold, &epoll_min_priority);
if (r == -EINTR) {
e->state = SD_EVENT_PENDING;
return 1;
}
if (r < 0)
goto finish;
if (r == 0 && threshold < INT64_MAX)
/* No new epoll event. */
break;
r = process_child(e, threshold, &child_min_priority);
if (r < 0)
goto finish;
if (r == 0 && threshold < INT64_MAX)
/* No new child event. */
break;
threshold = MIN(epoll_min_priority, child_min_priority);
if (threshold == INT64_MIN)
break;
timeout = 0;
}
r = process_watchdog(e);
@ -3959,19 +4031,12 @@ _public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
if (r < 0)
goto finish;
if (e->need_process_child) {
r = process_child(e);
if (r < 0)
goto finish;
}
r = process_inotify(e);
if (r < 0)
goto finish;
if (event_next_pending(e)) {
e->state = SD_EVENT_PENDING;
return 1;
}