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kqueue: don't arbitrarily restrict long-past values for NOTE_ABSTIME

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NOTE_ABSTIME values are converted to values relative to boottime in
filt_timervalidate(), and negative values are currently rejected.  We
don't reject times in the past in general, so clamp this up to 0 as
needed such that the timer fires immediately rather than imposing what
looks like an arbitrary restriction.

Another possible scenario is that the system clock had to be adjusted
by ~minutes or ~hours and we have less than that in terms of uptime,
making a reasonable short-timeout suddenly invalid. Firing it is still
a valid choice in this scenario so that applications can at least
expect a consistent behavior.

Reviewed by:	kib, markj
Discussed with:	allanjude
Differential Revision:	https://reviews.freebsd.org/D32230
This commit is contained in:
Kyle Evans 2021-09-29 14:55:59 -05:00
parent 1b7a2680fb
commit 9c999a259f
2 changed files with 92 additions and 3 deletions
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11
sys/kern/kern_event.c
View File

@ -798,13 +798,13 @@ filt_timervalidate(struct knote *kn, sbintime_t *to)
return (EINVAL);
*to = timer2sbintime(kn->kn_sdata, kn->kn_sfflags);
if (*to < 0)
return (EINVAL);
if ((kn->kn_sfflags & NOTE_ABSTIME) != 0) {
getboottimebin(&bt);
sbt = bttosbt(bt);
*to -= sbt;
*to = MAX(0, *to - sbt);
}
if (*to < 0)
return (EINVAL);
return (0);
}
@ -815,9 +815,14 @@ filt_timerattach(struct knote *kn)
sbintime_t to;
int error;
to = -1;
error = filt_timervalidate(kn, &to);
if (error != 0)
return (error);
KASSERT((kn->kn_flags & EV_ONESHOT) != 0 || to > 0,
("%s: periodic timer has a calculated zero timeout", __func__));
KASSERT(to >= 0,
("%s: timer has a calculated negative timeout", __func__));
if (atomic_fetchadd_int(&kq_ncallouts, 1) + 1 > kq_calloutmax) {
atomic_subtract_int(&kq_ncallouts, 1);

84
tests/sys/kqueue/libkqueue/timer.c
View File

@ -247,6 +247,88 @@ test_abstime(void)
success();
}
static void
test_abstime_preboot(void)
{
const char *test_id = "kevent(EVFILT_TIMER (PREBOOT), EV_ONESHOT, NOTE_ABSTIME)";
struct kevent kev;
struct timespec btp;
uint64_t end, start, stop;
test_begin(test_id);
test_no_kevents();
/*
* We'll expire it at just before system boot (roughly) with the hope that
* we'll get an ~immediate expiration, just as we do for any value specified
* between system boot and now.
*/
start = now();
if (clock_gettime(CLOCK_BOOTTIME, &btp) != 0)
err(1, "%s", test_id);
end = start - SEC_TO_US(btp.tv_sec + 1);
EV_SET(&kev, vnode_fd, EVFILT_TIMER, EV_ADD | EV_ONESHOT,
NOTE_ABSTIME | NOTE_USECONDS, end, NULL);
if (kevent(kqfd, &kev, 1, NULL, 0, NULL) < 0)
err(1, "%s", test_id);
/* Retrieve the event */
kev.flags = EV_ADD | EV_ONESHOT;
kev.data = 1;
kev.fflags = 0;
kevent_cmp(&kev, kevent_get(kqfd));
stop = now();
if (stop < end)
err(1, "too early %jd %jd", (intmax_t)stop, (intmax_t)end);
/* Check if the event occurs again */
sleep(3);
test_no_kevents();
success();
}
static void
test_abstime_postboot(void)
{
const char *test_id = "kevent(EVFILT_TIMER (POSTBOOT), EV_ONESHOT, NOTE_ABSTIME)";
struct kevent kev;
uint64_t end, start, stop;
const int timeout_sec = 1;
test_begin(test_id);
test_no_kevents();
/*
* Set a timer for 1 second ago, it should fire immediately rather than
* being rejected.
*/
start = now();
end = start - SEC_TO_US(timeout_sec);
EV_SET(&kev, vnode_fd, EVFILT_TIMER, EV_ADD | EV_ONESHOT,
NOTE_ABSTIME | NOTE_USECONDS, end, NULL);
if (kevent(kqfd, &kev, 1, NULL, 0, NULL) < 0)
err(1, "%s", test_id);
/* Retrieve the event */
kev.flags = EV_ADD | EV_ONESHOT;
kev.data = 1;
kev.fflags = 0;
kevent_cmp(&kev, kevent_get(kqfd));
stop = now();
if (stop < end)
err(1, "too early %jd %jd", (intmax_t)stop, (intmax_t)end);
/* Check if the event occurs again */
sleep(3);
test_no_kevents();
success();
}
static void
test_update(void)
{
@ -517,6 +599,8 @@ test_evfilt_timer(void)
test_oneshot();
test_periodic();
test_abstime();
test_abstime_preboot();
test_abstime_postboot();
test_update();
test_update_equal();
test_update_expired();