From f863f89d8a5cbb47676d5114e349918c4e009fe5 Mon Sep 17 00:00:00 2001

From: Lennart Poettering <lennart@poettering.net>

Date: Tue, 8 Jun 2021 00:07:51 -0700

Subject: [PATCH] sd-event: change ordering of pending/ratelimited events

Instead of ordering non-pending before pending we should order

"non-pending OR ratelimited" before "pending AND not-ratelimited".

This fixes a bug where ratelimited events were ordered at the end of the

priority queue and could be stuck there for an indeterminate amount of

time.

(cherry picked from commit 81107b8419c39f726fd2805517a5b9faab204e59)

Related: #1968528

---

 src/libsystemd/sd-event/sd-event.c | 48 +++++++++++++-----------------

 1 file changed, 20 insertions(+), 28 deletions(-)

diff --git a/src/libsystemd/sd-event/sd-event.c b/src/libsystemd/sd-event/sd-event.c

index be912d94e3..3e77f4e810 100644

--- a/src/libsystemd/sd-event/sd-event.c

+++ b/src/libsystemd/sd-event/sd-event.c

@@ -427,25 +427,6 @@ static usec_t time_event_source_next(const sd_event_source *s) {

         return USEC_INFINITY;

 }

-static int earliest_time_prioq_compare(const void *a, const void *b) {

-        const sd_event_source *x = a, *y = b;

-

-        /* Enabled ones first */

-        if (x->enabled != SD_EVENT_OFF && y->enabled == SD_EVENT_OFF)

-                return -1;

-        if (x->enabled == SD_EVENT_OFF && y->enabled != SD_EVENT_OFF)

-                return 1;

-

-        /* Move the pending ones to the end */

-        if (!x->pending && y->pending)

-                return -1;

-        if (x->pending && !y->pending)

-                return 1;

-

-        /* Order by time */

-        return CMP(time_event_source_next(x), time_event_source_next(y));

-}

-

 static usec_t time_event_source_latest(const sd_event_source *s) {

         assert(s);

@@ -464,7 +445,15 @@ static usec_t time_event_source_latest(const sd_event_source *s) {

         return USEC_INFINITY;

 }

-static int latest_time_prioq_compare(const void *a, const void *b) {

+static bool event_source_timer_candidate(const sd_event_source *s) {

+        assert(s);

+

+        /* Returns true for event sources that either are not pending yet (i.e. where it's worth to mark them pending)

+         * or which are currently ratelimited (i.e. where it's worth leaving the ratelimited state) */

+        return !s->pending || s->ratelimited;

+}

+

+static int time_prioq_compare(const void *a, const void *b, usec_t (*time_func)(const sd_event_source *s)) {

         const sd_event_source *x = a, *y = b;

         /* Enabled ones first */

@@ -473,19 +462,22 @@ static int latest_time_prioq_compare(const void *a, const void *b) {

         if (x->enabled == SD_EVENT_OFF && y->enabled != SD_EVENT_OFF)

                 return 1;

-        /* Move the pending ones to the end */

-        if (!x->pending && y->pending)

+        /* Order "non-pending OR ratelimited" before "pending AND not-ratelimited" */

+        if (event_source_timer_candidate(x) && !event_source_timer_candidate(y))

                 return -1;

-        if (x->pending && !y->pending)

+        if (!event_source_timer_candidate(x) && event_source_timer_candidate(y))

                 return 1;

         /* Order by time */

-        if (time_event_source_latest(x) < time_event_source_latest(y))

-                return -1;

-        if (time_event_source_latest(x) > time_event_source_latest(y))

-                return 1;

+        return CMP(time_func(x), time_func(y));

+}

-        return 0;

+static int earliest_time_prioq_compare(const void *a, const void *b) {

+        return time_prioq_compare(a, b, time_event_source_next);

+}

+

+static int latest_time_prioq_compare(const void *a, const void *b) {

+        return time_prioq_compare(a, b, time_event_source_latest);

 }

 static int exit_prioq_compare(const void *a, const void *b) {