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sd-event: always initialize sd_event.perturb

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If the boot ID cannot be obtained, let's first fallback to the machine
ID, and if still cannot, then let's use 0.
Otherwise, no timer event source cannot be triggered.

Fixes #26549.

(cherry picked from commit 6d2326e036)
(cherry picked from commit 58c821af60)
(cherry picked from commit 78976199b2)
This commit is contained in:
Yu Watanabe 2023-02-23 07:31:01 +09:00 committed by Zbigniew Jędrzejewski-Szmek
parent e385eb57dc
commit ac04d804c3
1 changed files with 10 additions and 11 deletions
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21
src/libsystemd/sd-event/sd-event.c
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@ -1126,22 +1126,21 @@ _public_ int sd_event_add_io(
}
static void initialize_perturb(sd_event *e) {
sd_id128_t bootid = {};
sd_id128_t id = {};
/* When we sleep for longer, we try to realign the wakeup to
the same time within each minute/second/250ms, so that
events all across the system can be coalesced into a single
CPU wakeup. However, let's take some system-specific
randomness for this value, so that in a network of systems
with synced clocks timer events are distributed a
bit. Here, we calculate a perturbation usec offset from the
boot ID. */
/* When we sleep for longer, we try to realign the wakeup to the same time within each
* minute/second/250ms, so that events all across the system can be coalesced into a single CPU
* wakeup. However, let's take some system-specific randomness for this value, so that in a network
* of systems with synced clocks timer events are distributed a bit. Here, we calculate a
* perturbation usec offset from the boot ID (or machine ID if failed, e.g. /proc is not mounted). */
if (_likely_(e->perturb != USEC_INFINITY))
return;
if (sd_id128_get_boot(&bootid) >= 0)
e->perturb = (bootid.qwords[0] ^ bootid.qwords[1]) % USEC_PER_MINUTE;
if (sd_id128_get_boot(&id) >= 0 || sd_id128_get_machine(&id) > 0)
e->perturb = (id.qwords[0] ^ id.qwords[1]) % USEC_PER_MINUTE;
else
e->perturb = 0; /* This is a super early process without /proc and /etc ?? */
}
static int event_setup_timer_fd(