sd-event: always initialize sd_event.perturb

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.

diff --git a/src/libsystemd/sd-event/sd-event.c b/src/libsystemd/sd-event/sd-event.c
index 2f9b0ecda06d3094ebb364bc60832de47730ee57..5303a14cd69f94550c060cbf6e75498f91f47964 100644 (file)
--- a/src/libsystemd/sd-event/sd-event.c
+++ b/src/libsystemd/sd-event/sd-event.c
@@ -1258,22 +1258,21 @@ _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(