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timer: make sure we use the right monotonic timestamp

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This reworks timer_enter_waiting() in a couple of ways in order to clean
it up a bit and fix #5629.

Most importantly, we previously we initialized ts_monotonic to either
the current time in CLOCK_MONOTONIC or in CLOCK_BOOTTIME, depending on
t->wake_system. Then given specific conditions we'd use this time as
base for our timers. And afterwards, if t->wake_system was on we'd
convetr the resulting value from CLOCK_MONOTONIC to CLOCK_BOOTTIME again
— which of course is wrong since we already were in CLOCK_BOOTTIME! This
fixes this logic, by using a triple timestamp so that we always have the
right base around, and initially only calculate in CLOCK_MONOTONIC and
only convert as last step.

Conversion between the clocks is now done with the generic
usec_shift_clock(), and additions via usec_add() making these
calculations a bit safer.

Fixes: #5629
This commit is contained in:
Lennart Poettering 2017-06-22 21:04:20 +02:00
parent 79fc8b9623
commit c54be90b28
1 changed files with 11 additions and 30 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
src/core/timer.c
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@ -316,21 +316,6 @@ static void timer_enter_elapsed(Timer *t, bool leave_around) {
timer_enter_dead(t, TIMER_SUCCESS);
}
static usec_t monotonic_to_boottime(usec_t t) {
usec_t a, b;
if (t <= 0)
return 0;
a = now(clock_boottime_or_monotonic());
b = now(CLOCK_MONOTONIC);
if (t + a > b)
return t + a - b;
else
return 0;
}
static void add_random(Timer *t, usec_t *v) {
char s[FORMAT_TIMESPAN_MAX];
usec_t add;
@ -355,9 +340,9 @@ static void add_random(Timer *t, usec_t *v) {
static void timer_enter_waiting(Timer *t, bool initial) {
bool found_monotonic = false, found_realtime = false;
usec_t ts_realtime, ts_monotonic;
usec_t base = 0;
bool leave_around = false;
triple_timestamp ts;
usec_t base = 0;
TimerValue *v;
Unit *trigger;
int r;
@ -371,11 +356,7 @@ static void timer_enter_waiting(Timer *t, bool initial) {
return;
}
/* If we shall wake the system we use the boottime clock
* rather than the monotonic clock. */
ts_realtime = now(CLOCK_REALTIME);
ts_monotonic = now(t->wake_system ? clock_boottime_or_monotonic() : CLOCK_MONOTONIC);
triple_timestamp_get(&ts);
t->next_elapse_monotonic_or_boottime = t->next_elapse_realtime = 0;
LIST_FOREACH(value, v, t->values) {
@ -391,7 +372,7 @@ static void timer_enter_waiting(Timer *t, bool initial) {
* to that. If we don't just start from
* now. */
b = t->last_trigger.realtime > 0 ? t->last_trigger.realtime : ts_realtime;
b = t->last_trigger.realtime > 0 ? t->last_trigger.realtime : ts.realtime;
r = calendar_spec_next_usec(v->calendar_spec, b, &v->next_elapse);
if (r < 0)
@ -405,13 +386,14 @@ static void timer_enter_waiting(Timer *t, bool initial) {
found_realtime = true;
} else {
switch (v->base) {
case TIMER_ACTIVE:
if (state_translation_table[t->state] == UNIT_ACTIVE)
base = UNIT(t)->inactive_exit_timestamp.monotonic;
else
base = ts_monotonic;
base = ts.monotonic;
break;
case TIMER_BOOT:
@ -456,12 +438,11 @@ static void timer_enter_waiting(Timer *t, bool initial) {
assert_not_reached("Unknown timer base");
}
if (t->wake_system)
base = monotonic_to_boottime(base);
v->next_elapse = usec_add(usec_shift_clock(base, CLOCK_MONOTONIC, TIMER_MONOTONIC_CLOCK(t)), v->value);
v->next_elapse = base + v->value;
if (!initial && v->next_elapse < ts_monotonic && IN_SET(v->base, TIMER_ACTIVE, TIMER_BOOT, TIMER_STARTUP)) {
if (!initial &&
v->next_elapse < triple_timestamp_by_clock(&ts, TIMER_MONOTONIC_CLOCK(t)) &&
IN_SET(v->base, TIMER_ACTIVE, TIMER_BOOT, TIMER_STARTUP)) {
/* This is a one time trigger, disable it now */
v->disabled = true;
continue;
@ -488,7 +469,7 @@ static void timer_enter_waiting(Timer *t, bool initial) {
add_random(t, &t->next_elapse_monotonic_or_boottime);
left = t->next_elapse_monotonic_or_boottime > ts_monotonic ? t->next_elapse_monotonic_or_boottime - ts_monotonic : 0;
left = usec_sub_unsigned(t->next_elapse_monotonic_or_boottime, triple_timestamp_by_clock(&ts, TIMER_MONOTONIC_CLOCK(t)));
log_unit_debug(UNIT(t), "Monotonic timer elapses in %s.", format_timespan(buf, sizeof(buf), left, 0));
if (t->monotonic_event_source) {