From 6ffe3a31b89d8fcdffcad3235038c40f5e75356c Mon Sep 17 00:00:00 2001 From: Jake Freeland Date: Fri, 20 Mar 2026 01:33:03 -0500 Subject: [PATCH] timerfd: Fix interval callout scheduling When a timerfd interval callout misses its scheduled activation time, a differential is calculated based on the actual activation time and the scheduled activation time. This differential is divided by the timerfd's interval time and the quotient is added to the timerfd's counter. Before this change, the next callout was scheduled to activate at: scheduled activation time + timerfd interval. This change fixes the scheduling of the next callout to activate at: actual activation time + timerfd interval - remainder. Security: FreeBSD-26:06.timerfd Approved by: so Reviewed by: markj Differential Revision: https://reviews.freebsd.org/D55790 MFC after: 2 weeks (cherry picked from commit 85c0f1a87da1fd1eb3e646e86f70e630c48da91a) (cherry picked from commit 3c00f603a2801fd780666f9e94a26f264a887c90) --- sys/kern/sys_timerfd.c | 24 +++++++++++++----------- 1 file changed, 13 insertions(+), 11 deletions(-) diff --git a/sys/kern/sys_timerfd.c b/sys/kern/sys_timerfd.c index ab7e048a2ab..59c554f2dba 100644 --- a/sys/kern/sys_timerfd.c +++ b/sys/kern/sys_timerfd.c @@ -394,23 +394,25 @@ static void timerfd_expire(void *arg) { struct timerfd *tfd = (struct timerfd *)arg; - struct timespec uptime; + sbintime_t exp, interval, now, next, diff; ++tfd->tfd_count; tfd->tfd_expired = true; if (timespecisset(&tfd->tfd_time.it_interval)) { + exp = tstosbt(tfd->tfd_time.it_value); + interval = tstosbt(tfd->tfd_time.it_interval); + now = sbinuptime(); + next = now + interval; + /* Count missed events. */ - nanouptime(&uptime); - if (timespeccmp(&uptime, &tfd->tfd_time.it_value, >)) { - timespecsub(&uptime, &tfd->tfd_time.it_value, &uptime); - tfd->tfd_count += tstosbt(uptime) / - tstosbt(tfd->tfd_time.it_interval); + if (now > exp) { + diff = now - exp; + tfd->tfd_count += diff / interval; + next -= diff % interval; } - timespecadd(&tfd->tfd_time.it_value, - &tfd->tfd_time.it_interval, &tfd->tfd_time.it_value); - callout_schedule_sbt(&tfd->tfd_callout, - tstosbt(tfd->tfd_time.it_value), - 0, C_ABSOLUTE); + + callout_schedule_sbt(&tfd->tfd_callout, next, 0, C_ABSOLUTE); + tfd->tfd_time.it_value = sbttots(next); } else { /* Single shot timer. */ callout_deactivate(&tfd->tfd_callout);