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https://github.com/systemd/systemd-stable.git
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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
Lennart Poettering
parent
e62636741c
commit
efd3be9de1
@ -1039,7 +1039,7 @@ static int source_set_pending(sd_event_source *s, bool b) {
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}
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}
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return 0;
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return 1;
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}
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static sd_event_source *source_new(sd_event *e, bool floating, EventSourceType type) {
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@ -3116,11 +3116,19 @@ static int process_timer(
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return 0;
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}
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static int process_child(sd_event *e) {
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static int process_child(sd_event *e, int64_t threshold, int64_t *ret_min_priority) {
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int64_t min_priority = threshold;
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bool something_new = false;
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sd_event_source *s;
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int r;
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assert(e);
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assert(ret_min_priority);
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if (!e->need_process_child) {
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*ret_min_priority = min_priority;
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return 0;
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}
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e->need_process_child = false;
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@ -3145,6 +3153,9 @@ static int process_child(sd_event *e) {
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HASHMAP_FOREACH(s, e->child_sources) {
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assert(s->type == SOURCE_CHILD);
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if (s->priority > threshold)
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continue;
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if (s->pending)
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continue;
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@ -3181,10 +3192,15 @@ static int process_child(sd_event *e) {
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r = source_set_pending(s, true);
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if (r < 0)
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return r;
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if (r > 0) {
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something_new = true;
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min_priority = MIN(min_priority, s->priority);
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}
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}
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}
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return 0;
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*ret_min_priority = min_priority;
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return something_new;
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}
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static int process_pidfd(sd_event *e, sd_event_source *s, uint32_t revents) {
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@ -3214,13 +3230,13 @@ static int process_pidfd(sd_event *e, sd_event_source *s, uint32_t revents) {
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return source_set_pending(s, true);
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}
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static int process_signal(sd_event *e, struct signal_data *d, uint32_t events) {
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bool read_one = false;
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static int process_signal(sd_event *e, struct signal_data *d, uint32_t events, int64_t *min_priority) {
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int r;
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assert(e);
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assert(d);
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assert_return(events == EPOLLIN, -EIO);
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assert(min_priority);
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/* If there's a signal queued on this priority and SIGCHLD is
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on this priority too, then make sure to recheck the
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@ -3246,7 +3262,7 @@ static int process_signal(sd_event *e, struct signal_data *d, uint32_t events) {
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n = read(d->fd, &si, sizeof(si));
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if (n < 0) {
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if (IN_SET(errno, EAGAIN, EINTR))
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return read_one;
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return 0;
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return -errno;
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}
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@ -3256,8 +3272,6 @@ static int process_signal(sd_event *e, struct signal_data *d, uint32_t events) {
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assert(SIGNAL_VALID(si.ssi_signo));
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read_one = true;
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if (e->signal_sources)
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s = e->signal_sources[si.ssi_signo];
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if (!s)
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@ -3271,12 +3285,16 @@ static int process_signal(sd_event *e, struct signal_data *d, uint32_t events) {
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r = source_set_pending(s, true);
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if (r < 0)
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return r;
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if (r > 0 && *min_priority >= s->priority) {
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*min_priority = s->priority;
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return 1; /* an event source with smaller priority is queued. */
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}
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return 1;
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return 0;
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}
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}
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static int event_inotify_data_read(sd_event *e, struct inotify_data *d, uint32_t revents) {
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static int event_inotify_data_read(sd_event *e, struct inotify_data *d, uint32_t revents, int64_t threshold) {
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ssize_t n;
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assert(e);
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@ -3292,6 +3310,9 @@ static int event_inotify_data_read(sd_event *e, struct inotify_data *d, uint32_t
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if (d->buffer_filled > 0)
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return 0;
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if (d->priority > threshold)
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return 0;
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n = read(d->fd, &d->buffer, sizeof(d->buffer));
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if (n < 0) {
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if (IN_SET(errno, EAGAIN, EINTR))
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@ -3831,20 +3852,14 @@ static int epoll_wait_usec(
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return r;
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}
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_public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
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static int process_epoll(sd_event *e, usec_t timeout, int64_t threshold, int64_t *ret_min_priority) {
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int64_t min_priority = threshold;
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bool something_new = false;
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size_t n_event_queue, m;
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int r;
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assert_return(e, -EINVAL);
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assert_return(e = event_resolve(e), -ENOPKG);
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assert_return(!event_pid_changed(e), -ECHILD);
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assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
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assert_return(e->state == SD_EVENT_ARMED, -EBUSY);
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if (e->exit_requested) {
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e->state = SD_EVENT_PENDING;
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return 1;
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}
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assert(e);
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assert(ret_min_priority);
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n_event_queue = MAX(e->n_sources, 1u);
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if (!GREEDY_REALLOC(e->event_queue, e->event_queue_allocated, n_event_queue))
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@ -3856,12 +3871,8 @@ _public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
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for (;;) {
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r = epoll_wait_usec(e->epoll_fd, e->event_queue, e->event_queue_allocated, timeout);
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if (r == -EINTR) {
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e->state = SD_EVENT_PENDING;
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return 1;
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}
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if (r < 0)
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goto finish;
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return r;
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m = (size_t) r;
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@ -3877,7 +3888,9 @@ _public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
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timeout = 0;
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}
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triple_timestamp_get(&e->timestamp);
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/* Set timestamp only when this is called first time. */
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if (threshold == INT64_MAX)
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triple_timestamp_get(&e->timestamp);
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for (size_t i = 0; i < m; i++) {
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@ -3893,6 +3906,11 @@ _public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
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assert(s);
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if (s->priority > threshold)
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continue;
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min_priority = MIN(min_priority, s->priority);
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switch (s->type) {
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case SOURCE_IO:
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@ -3920,19 +3938,75 @@ _public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
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}
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case WAKEUP_SIGNAL_DATA:
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r = process_signal(e, e->event_queue[i].data.ptr, e->event_queue[i].events);
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r = process_signal(e, e->event_queue[i].data.ptr, e->event_queue[i].events, &min_priority);
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break;
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case WAKEUP_INOTIFY_DATA:
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r = event_inotify_data_read(e, e->event_queue[i].data.ptr, e->event_queue[i].events);
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r = event_inotify_data_read(e, e->event_queue[i].data.ptr, e->event_queue[i].events, threshold);
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break;
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default:
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assert_not_reached("Invalid wake-up pointer");
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}
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}
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if (r < 0)
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return r;
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if (r > 0)
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something_new = true;
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}
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*ret_min_priority = min_priority;
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return something_new;
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}
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_public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
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int r;
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assert_return(e, -EINVAL);
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assert_return(e = event_resolve(e), -ENOPKG);
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assert_return(!event_pid_changed(e), -ECHILD);
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assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
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assert_return(e->state == SD_EVENT_ARMED, -EBUSY);
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if (e->exit_requested) {
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e->state = SD_EVENT_PENDING;
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return 1;
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}
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for (int64_t threshold = INT64_MAX; ; threshold--) {
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int64_t epoll_min_priority, child_min_priority;
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/* There may be a possibility that new epoll (especially IO) and child events are
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* triggered just after process_epoll() call but before process_child(), and the new IO
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* events may have higher priority than the child events. To salvage these events,
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* let's call epoll_wait() again, but accepts only events with higher priority than the
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* previous. See issue https://github.com/systemd/systemd/issues/18190 and comments
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* https://github.com/systemd/systemd/pull/18750#issuecomment-785801085
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* https://github.com/systemd/systemd/pull/18922#issuecomment-792825226 */
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r = process_epoll(e, timeout, threshold, &epoll_min_priority);
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if (r == -EINTR) {
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e->state = SD_EVENT_PENDING;
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return 1;
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}
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if (r < 0)
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goto finish;
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if (r == 0 && threshold < INT64_MAX)
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/* No new epoll event. */
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break;
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r = process_child(e, threshold, &child_min_priority);
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if (r < 0)
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goto finish;
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if (r == 0)
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/* No new child event. */
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break;
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threshold = MIN(epoll_min_priority, child_min_priority);
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if (threshold == INT64_MIN)
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break;
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timeout = 0;
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}
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r = process_watchdog(e);
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@ -3959,19 +4033,12 @@ _public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
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if (r < 0)
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goto finish;
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if (e->need_process_child) {
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r = process_child(e);
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if (r < 0)
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goto finish;
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}
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r = process_inotify(e);
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if (r < 0)
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goto finish;
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if (event_next_pending(e)) {
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e->state = SD_EVENT_PENDING;
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return 1;
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}
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