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From f863f89d8a5cbb47676d5114e349918c4e009fe5 Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Tue, 8 Jun 2021 00:07:51 -0700
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Subject: [PATCH] sd-event: change ordering of pending/ratelimited events
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Instead of ordering non-pending before pending we should order
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"non-pending OR ratelimited" before "pending AND not-ratelimited".
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This fixes a bug where ratelimited events were ordered at the end of the
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priority queue and could be stuck there for an indeterminate amount of
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time.
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(cherry picked from commit 81107b8419c39f726fd2805517a5b9faab204e59)
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698723
Related: #1968528
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---
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 src/libsystemd/sd-event/sd-event.c | 48 +++++++++++++-----------------
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 1 file changed, 20 insertions(+), 28 deletions(-)
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diff --git a/src/libsystemd/sd-event/sd-event.c b/src/libsystemd/sd-event/sd-event.c
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index be912d94e3..3e77f4e810 100644
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--- a/src/libsystemd/sd-event/sd-event.c
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+++ b/src/libsystemd/sd-event/sd-event.c
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@@ -427,25 +427,6 @@ static usec_t time_event_source_next(const sd_event_source *s) {
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         return USEC_INFINITY;
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 }
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-static int earliest_time_prioq_compare(const void *a, const void *b) {
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-        const sd_event_source *x = a, *y = b;
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-
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-        /* Enabled ones first */
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-        if (x->enabled != SD_EVENT_OFF && y->enabled == SD_EVENT_OFF)
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-                return -1;
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-        if (x->enabled == SD_EVENT_OFF && y->enabled != SD_EVENT_OFF)
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-                return 1;
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-
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-        /* Move the pending ones to the end */
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-        if (!x->pending && y->pending)
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-                return -1;
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-        if (x->pending && !y->pending)
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-                return 1;
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-
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-        /* Order by time */
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-        return CMP(time_event_source_next(x), time_event_source_next(y));
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-}
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-
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 static usec_t time_event_source_latest(const sd_event_source *s) {
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         assert(s);
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@@ -464,7 +445,15 @@ static usec_t time_event_source_latest(const sd_event_source *s) {
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         return USEC_INFINITY;
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 }
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-static int latest_time_prioq_compare(const void *a, const void *b) {
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+static bool event_source_timer_candidate(const sd_event_source *s) {
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+        assert(s);
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+
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+        /* Returns true for event sources that either are not pending yet (i.e. where it's worth to mark them pending)
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+         * or which are currently ratelimited (i.e. where it's worth leaving the ratelimited state) */
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+        return !s->pending || s->ratelimited;
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+}
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+
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+static int time_prioq_compare(const void *a, const void *b, usec_t (*time_func)(const sd_event_source *s)) {
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         const sd_event_source *x = a, *y = b;
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         /* Enabled ones first */
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@@ -473,19 +462,22 @@ static int latest_time_prioq_compare(const void *a, const void *b) {
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         if (x->enabled == SD_EVENT_OFF && y->enabled != SD_EVENT_OFF)
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                 return 1;
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-        /* Move the pending ones to the end */
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-        if (!x->pending && y->pending)
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+        /* Order "non-pending OR ratelimited" before "pending AND not-ratelimited" */
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+        if (event_source_timer_candidate(x) && !event_source_timer_candidate(y))
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                 return -1;
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-        if (x->pending && !y->pending)
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+        if (!event_source_timer_candidate(x) && event_source_timer_candidate(y))
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                 return 1;
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         /* Order by time */
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-        if (time_event_source_latest(x) < time_event_source_latest(y))
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-                return -1;
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-        if (time_event_source_latest(x) > time_event_source_latest(y))
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-                return 1;
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+        return CMP(time_func(x), time_func(y));
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+}
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-        return 0;
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+static int earliest_time_prioq_compare(const void *a, const void *b) {
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+        return time_prioq_compare(a, b, time_event_source_next);
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+}
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+
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+static int latest_time_prioq_compare(const void *a, const void *b) {
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+        return time_prioq_compare(a, b, time_event_source_latest);
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 }
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 static int exit_prioq_compare(const void *a, const void *b) {