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Index: share/man/man9/sleep.9
===================================================================
--- share/man/man9/sleep.9
+++ share/man/man9/sleep.9
@@ -280,6 +280,21 @@
pay particular attention to ensure that no other threads wait on the
same
.Fa chan .
+.Pp
+If the timeout given by
+.Fa timo
+or
+.Fa sbt
+is based on an absolute real-time clock value,
+then the thread should copy the global
+.Va rtc_generation
+into its
+.Va td_rtcgen
+member before reading the RTC.
+If the real-time clock is adjusted, these functions will set
+.Va td_rtcgen
+to zero and return zero.
+The caller should reconsider its orientation with the new RTC value.
.Sh RETURN VALUES
When awakened by a call to
.Fn wakeup
@@ -298,6 +313,9 @@
.Fn msleep_spin ,
.Fn tsleep ,
and locking primitive sleep functions return 0.
+Zero can also be returned when the real-time clock is adjusted;
+see above regarding
+.Va td_rtcgen .
Otherwise, a non-zero error code is returned.
.Sh ERRORS
.Fn msleep ,
Index: sys/kern/kern_tc.c
===================================================================
--- sys/kern/kern_tc.c
+++ sys/kern/kern_tc.c
@@ -28,7 +28,9 @@
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/mutex.h>
+#include <sys/proc.h>
#include <sys/sbuf.h>
+#include <sys/sleepqueue.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>
#include <sys/systm.h>
@@ -126,6 +128,8 @@
sysctl_kern_timecounter_adjprecision, "I",
"Allowed time interval deviation in percents");
+volatile int rtc_generation = 1;
+
static int tc_chosen; /* Non-zero if a specific tc was chosen via sysctl. */
static void tc_windup(struct bintime *new_boottimebin);
@@ -1261,6 +1265,26 @@
return (timehands->th_counter->tc_frequency);
}
+static bool
+sleeping_on_old_rtc(struct thread *td)
+{
+
+ /*
+ * td_rtcgen is modified by curthread when it is running,
+ * and by other threads in this function. By finding the thread
+ * on a sleepqueue and holding the lock on the sleepqueue
+ * chain, we guarantee that the thread is not running and that
+ * modifying td_rtcgen is safe. Setting td_rtcgen to zero informs
+ * the thread that it was woken due to a real-time clock adjustment.
+ * (The declaration of td_rtcgen refers to this comment.)
+ */
+ if (td->td_rtcgen != 0 && td->td_rtcgen != rtc_generation) {
+ td->td_rtcgen = 0;
+ return (true);
+ }
+ return (false);
+}
+
static struct mtx tc_setclock_mtx;
MTX_SYSINIT(tc_setclock_init, &tc_setclock_mtx, "tcsetc", MTX_SPIN);
@@ -1284,6 +1308,10 @@
/* XXX fiddle all the little crinkly bits around the fiords... */
tc_windup(&bt);
mtx_unlock_spin(&tc_setclock_mtx);
+
+ /* Avoid rtc_generation == 0, since td_rtcgen == 0 is special. */
+ atomic_add_rel_int(&rtc_generation, 2);
+ sleepq_chains_remove_matching(sleeping_on_old_rtc);
if (timestepwarnings) {
nanotime(&taft);
log(LOG_INFO,
Index: sys/kern/kern_umtx.c
===================================================================
--- sys/kern/kern_umtx.c
+++ sys/kern/kern_umtx.c
@@ -59,6 +59,7 @@
#include <sys/sysproto.h>
#include <sys/syscallsubr.h>
#include <sys/taskqueue.h>
+#include <sys/time.h>
#include <sys/eventhandler.h>
#include <sys/umtx.h>
@@ -70,6 +71,7 @@
#include <vm/vm_map.h>
#include <vm/vm_object.h>
+#include <machine/atomic.h>
#include <machine/cpu.h>
#ifdef COMPAT_FREEBSD32
@@ -210,6 +212,7 @@
struct abs_timeout {
int clockid;
+ bool is_abs_real; /* TIMER_ABSTIME && CLOCK_REALTIME* */
struct timespec cur;
struct timespec end;
};
@@ -257,6 +260,8 @@
static SYSCTL_NODE(_debug_umtx, OID_AUTO, chains, CTLFLAG_RD, 0, "umtx chain stats");
#endif
+static void abs_timeout_update(struct abs_timeout *timo);
+
static void umtx_shm_init(void);
static void umtxq_sysinit(void *);
static void umtxq_hash(struct umtx_key *key);
@@ -772,12 +777,22 @@
timo->clockid = clockid;
if (!absolute) {
- kern_clock_gettime(curthread, clockid, &timo->end);
- timo->cur = timo->end;
+ timo->is_abs_real = false;
+ abs_timeout_update(timo);
+ timo->end = timo->cur;
timespecadd(&timo->end, timeout);
} else {
timo->end = *timeout;
- kern_clock_gettime(curthread, clockid, &timo->cur);
+ timo->is_abs_real = clockid == CLOCK_REALTIME ||
+ clockid == CLOCK_REALTIME_FAST ||
+ clockid == CLOCK_REALTIME_PRECISE;
+ /*
+ * If is_abs_real, umtxq_sleep will read the clock
+ * after setting td_rtcgen; otherwise, read it here.
+ */
+ if (!timo->is_abs_real) {
+ abs_timeout_update(timo);
+ }
}
}
@@ -831,26 +846,41 @@
struct umtxq_chain *uc;
int error, timo;
+ if (abstime != NULL && abstime->is_abs_real) {
+ curthread->td_rtcgen = atomic_load_acq_int(&rtc_generation);
+ abs_timeout_update(abstime);
+ }
+
uc = umtxq_getchain(&uq->uq_key);
UMTXQ_LOCKED_ASSERT(uc);
for (;;) {
- if (!(uq->uq_flags & UQF_UMTXQ))
- return (0);
+ if (!(uq->uq_flags & UQF_UMTXQ)) {
+ error = 0;
+ break;
+ }
if (abstime != NULL) {
timo = abs_timeout_gethz(abstime);
- if (timo < 0)
- return (ETIMEDOUT);
+ if (timo < 0) {
+ error = ETIMEDOUT;
+ break;
+ }
} else
timo = 0;
error = msleep(uq, &uc->uc_lock, PCATCH | PDROP, wmesg, timo);
- if (error != EWOULDBLOCK) {
+ if (error == EINTR || error == ERESTART) {
umtxq_lock(&uq->uq_key);
break;
}
- if (abstime != NULL)
+ if (abstime != NULL) {
+ if (abstime->is_abs_real)
+ curthread->td_rtcgen =
+ atomic_load_acq_int(&rtc_generation);
abs_timeout_update(abstime);
+ }
umtxq_lock(&uq->uq_key);
}
+
+ curthread->td_rtcgen = 0;
return (error);
}
Index: sys/kern/subr_sleepqueue.c
===================================================================
--- sys/kern/subr_sleepqueue.c
+++ sys/kern/subr_sleepqueue.c
@@ -78,6 +78,9 @@
#include <sys/sleepqueue.h>
#include <sys/stack.h>
#include <sys/sysctl.h>
+#include <sys/time.h>
+
+#include <machine/atomic.h>
#include <vm/uma.h>
@@ -539,6 +542,7 @@
struct sleepqueue_chain *sc;
struct sleepqueue *sq;
struct thread *td;
+ bool rtc_changed;
td = curthread;
sc = SC_LOOKUP(wchan);
@@ -558,8 +562,26 @@
* If TDF_TIMEOUT is set, then our sleep has been timed out
* already but we are still on the sleep queue, so dequeue the
* thread and return.
+ *
+ * Do the same if the real-time clock has been adjusted since this
+ * thread calculated its timeout based on that clock. This handles
+ * the following race:
+ * - The Ts thread needs to sleep until an absolute real-clock time.
+ * It copies the global rtc_generation into curthread->td_rtcgen,
+ * reads the RTC, and calculates a sleep duration based on that time.
+ * See umtxq_sleep() for an example.
+ * - The Tc thread adjusts the RTC, bumps rtc_generation, and wakes
+ * threads that are sleeping until an absolute real-clock time.
+ * See tc_setclock() and the POSIX specification of clock_settime().
+ * - Ts reaches the code below. It holds the sleepqueue chain lock,
+ * so Tc has finished waking, so this thread must test td_rtcgen.
+ * (The declaration of td_rtcgen refers to this comment.)
*/
- if (td->td_flags & TDF_TIMEOUT) {
+ rtc_changed = td->td_rtcgen != 0 && td->td_rtcgen != rtc_generation;
+ if ((td->td_flags & TDF_TIMEOUT) || rtc_changed) {
+ if (rtc_changed) {
+ td->td_rtcgen = 0;
+ }
MPASS(TD_ON_SLEEPQ(td));
sq = sleepq_lookup(wchan);
if (sleepq_resume_thread(sq, td, 0)) {
@@ -886,6 +908,13 @@
return (wakeup_swapper);
}
+static bool
+match_any(struct thread *td __unused)
+{
+
+ return (true);
+}
+
/*
* Resume all threads sleeping on a specified wait channel.
*/
@@ -893,8 +922,6 @@
sleepq_broadcast(void *wchan, int flags, int pri, int queue)
{
struct sleepqueue *sq;
- struct thread *td, *tdn;
- int wakeup_swapper;
CTR2(KTR_PROC, "sleepq_broadcast(%p, %d)", wchan, flags);
KASSERT(wchan != NULL, ("%s: invalid NULL wait channel", __func__));
@@ -905,18 +932,33 @@
KASSERT(sq->sq_type == (flags & SLEEPQ_TYPE),
("%s: mismatch between sleep/wakeup and cv_*", __func__));
+ return (sleepq_remove_matching(sq, queue, match_any, pri));
+}
+
+/*
+ * Resume threads on the sleep queue that match the given predicate.
+ */
+int
+sleepq_remove_matching(struct sleepqueue *sq, int queue,
+ bool (*matches)(struct thread *), int pri)
+{
+ struct thread *td, *tdn;
+ int wakeup_swapper;
+
/*
- * Resume all blocked threads on the sleep queue. The last thread will
- * be given ownership of sq and may re-enqueue itself before
- * sleepq_resume_thread() returns, so we must cache the "next" queue
- * item at the beginning of the final iteration.
+ * The last thread will be given ownership of sq and may
+ * re-enqueue itself before sleepq_resume_thread() returns,
+ * so we must cache the "next" queue item at the beginning
+ * of the final iteration.
*/
wakeup_swapper = 0;
TAILQ_FOREACH_SAFE(td, &sq->sq_blocked[queue], td_slpq, tdn) {
thread_lock(td);
- wakeup_swapper |= sleepq_resume_thread(sq, td, pri);
+ if (matches(td))
+ wakeup_swapper |= sleepq_resume_thread(sq, td, pri);
thread_unlock(td);
}
+
return (wakeup_swapper);
}
@@ -1052,6 +1094,32 @@
return (sleepq_resume_thread(sq, td, 0));
}
+void
+sleepq_chains_remove_matching(bool (*matches)(struct thread *))
+{
+ struct sleepqueue_chain *sc;
+ struct sleepqueue *sq;
+ int i, wakeup_swapper;
+
+ wakeup_swapper = 0;
+ for (sc = &sleepq_chains[0]; sc < sleepq_chains + SC_TABLESIZE; ++sc) {
+ if (LIST_EMPTY(&sc->sc_queues)) {
+ continue;
+ }
+ mtx_lock_spin(&sc->sc_lock);
+ LIST_FOREACH(sq, &sc->sc_queues, sq_hash) {
+ for (i = 0; i < NR_SLEEPQS; ++i) {
+ wakeup_swapper |= sleepq_remove_matching(sq, i,
+ matches, 0);
+ }
+ }
+ mtx_unlock_spin(&sc->sc_lock);
+ }
+ if (wakeup_swapper) {
+ kick_proc0();
+ }
+}
+
/*
* Prints the stacks of all threads presently sleeping on wchan/queue to
* the sbuf sb. Sets count_stacks_printed to the number of stacks actually
Index: sys/sys/proc.h
===================================================================
--- sys/sys/proc.h
+++ sys/sys/proc.h
@@ -148,6 +148,7 @@
* o - ktrace lock
* q - td_contested lock
* r - p_peers lock
+ * s - see sleepq_switch(), sleeping_on_old_rtc(), and sleep(9)
* t - thread lock
* u - process stat lock
* w - process timer lock
@@ -283,6 +284,7 @@
int td_dom_rr_idx; /* (k) RR Numa domain selection. */
void *td_su; /* (k) FFS SU private */
sbintime_t td_sleeptimo; /* (t) Sleep timeout. */
+ int td_rtcgen; /* (s) rtc_generation of abs. sleep */
#define td_endzero td_sigmask
/* Copied during fork1() or create_thread(). */
Index: sys/sys/sleepqueue.h
===================================================================
--- sys/sys/sleepqueue.h
+++ sys/sys/sleepqueue.h
@@ -90,11 +90,14 @@
int flags, int queue);
struct sleepqueue *sleepq_alloc(void);
int sleepq_broadcast(void *wchan, int flags, int pri, int queue);
+void sleepq_chains_remove_matching(bool (*matches)(struct thread *));
void sleepq_free(struct sleepqueue *sq);
void sleepq_lock(void *wchan);
struct sleepqueue *sleepq_lookup(void *wchan);
void sleepq_release(void *wchan);
void sleepq_remove(struct thread *td, void *wchan);
+int sleepq_remove_matching(struct sleepqueue *sq, int queue,
+ bool (*matches)(struct thread *), int pri);
int sleepq_signal(void *wchan, int flags, int pri, int queue);
void sleepq_set_timeout_sbt(void *wchan, sbintime_t sbt,
sbintime_t pr, int flags);
Index: sys/sys/time.h
===================================================================
--- sys/sys/time.h
+++ sys/sys/time.h
@@ -383,6 +383,8 @@
extern sbintime_t sbt_timethreshold;
extern sbintime_t sbt_tickthreshold;
+extern volatile int rtc_generation;
+
/*
* Functions for looking at our clock: [get]{bin,nano,micro}[up]time()
*

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