Revert: Unify CLOCK_MONOTONIC and CLOCK_BOOTTIME

Revert commits

92af4dcb4e1c ("tracing: Unify the "boot" and "mono" tracing clocks")
127bfa5f4342 ("hrtimer: Unify MONOTONIC and BOOTTIME clock behavior")
7250a4047aa6 ("posix-timers: Unify MONOTONIC and BOOTTIME clock behavior")
d6c7270e913d ("timekeeping: Remove boot time specific code")
f2d6fdbfd238 ("Input: Evdev - unify MONOTONIC and BOOTTIME clock behavior")
d6ed449afdb3 ("timekeeping: Make the MONOTONIC clock behave like the BOOTTIME clock")
72199320d49d ("timekeeping: Add the new CLOCK_MONOTONIC_ACTIVE clock")

As stated in the pull request for the unification of CLOCK_MONOTONIC and
CLOCK_BOOTTIME, it was clear that we might have to revert the change.

As reported by several folks systemd and other applications rely on the
documented behaviour of CLOCK_MONOTONIC on Linux and break with the above
changes. After resume daemons time out and other timeout related issues are
observed. Rafael compiled this list:

* systemd kills daemons on resume, after >WatchdogSec seconds
of suspending (Genki Sky). [Verified that that's because systemd uses
CLOCK_MONOTONIC and expects it to not include the suspend time.]

* systemd-journald misbehaves after resume:
systemd-journald[7266]: File /var/log/journal/016627c3c4784cd4812d4b7e96a34226/system.journal
corrupted or uncleanly shut down, renaming and replacing.
(Mike Galbraith).

* NetworkManager reports "networking disabled" and networking is broken
after resume 50% of the time (Pavel). [May be because of systemd.]

* MATE desktop dims the display and starts the screensaver right after
system resume (Pavel).

* Full system hang during resume (me). [May be due to systemd or NM or both.]

That happens on debian and open suse systems.

It's sad, that these problems were neither catched in -next nor by those
folks who expressed interest in this change.

Reported-by: Rafael J. Wysocki <[e-mail]>
Reported-by: Genki Sky <[e-mail]>,
Reported-by: Pavel Machek <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Cc: Dmitry Torokhov <[e-mail]>
Cc: John Stultz <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Kevin Easton <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Mark Salyzyn <[e-mail]>
Cc: Michael Kerrisk <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Petr Mladek <[e-mail]>
Cc: Prarit Bhargava <[e-mail]>
Cc: Sergey Senozhatsky <[e-mail]>
Cc: Steven Rostedt <[e-mail]>

Documentation/trace/ftrace.rst

···
 		and ticks at the same rate as the hardware clocksource.
 
 	boot:
-		Same as mono. Used to be a separate clock which accounted
-		for the time spent in suspend while CLOCK_MONOTONIC did
-		not.
+		This is the boot clock (CLOCK_BOOTTIME) and is based on the
+		fast monotonic clock, but also accounts for time spent in
+		suspend. Since the clock access is designed for use in
+		tracing in the suspend path, some side effects are possible
+		if clock is accessed after the suspend time is accounted before
+		the fast mono clock is updated. In this case, the clock update
+		appears to happen slightly sooner than it normally would have.
+		Also on 32-bit systems, it's possible that the 64-bit boot offset
+		sees a partial update. These effects are rare and post
+		processing should be able to handle them. See comments in the
+		ktime_get_boot_fast_ns() function for more information.
 
 	To set a clock, simply echo the clock name into this file::
 

drivers/input/evdev.c

···
 enum evdev_clock_type {
 	EV_CLK_REAL = 0,
 	EV_CLK_MONO,
+	EV_CLK_BOOT,
 	EV_CLK_MAX
 };
 
···
 	case CLOCK_REALTIME:
 		clk_type = EV_CLK_REAL;
 		break;
-	case CLOCK_BOOTTIME:
 	case CLOCK_MONOTONIC:
 		clk_type = EV_CLK_MONO;
+		break;
+	case CLOCK_BOOTTIME:
+		clk_type = EV_CLK_BOOT;
 		break;
 	default:
 		return -EINVAL;
···
 
 	ev_time[EV_CLK_MONO] = ktime_get();
 	ev_time[EV_CLK_REAL] = ktime_mono_to_real(ev_time[EV_CLK_MONO]);
+	ev_time[EV_CLK_BOOT] = ktime_mono_to_any(ev_time[EV_CLK_MONO],
+						 TK_OFFS_BOOT);
 
 	rcu_read_lock();
 

include/linux/hrtimer.h

···
 enum  hrtimer_base_type {
 	HRTIMER_BASE_MONOTONIC,
 	HRTIMER_BASE_REALTIME,
+	HRTIMER_BASE_BOOTTIME,
 	HRTIMER_BASE_TAI,
 	HRTIMER_BASE_MONOTONIC_SOFT,
 	HRTIMER_BASE_REALTIME_SOFT,
+	HRTIMER_BASE_BOOTTIME_SOFT,
 	HRTIMER_BASE_TAI_SOFT,
 	HRTIMER_MAX_CLOCK_BASES,
 };

include/linux/timekeeper_internal.h

···
  * @offs_real:		Offset clock monotonic -> clock realtime
  * @offs_boot:		Offset clock monotonic -> clock boottime
  * @offs_tai:		Offset clock monotonic -> clock tai
- * @time_suspended:	Accumulated suspend time
  * @tai_offset:		The current UTC to TAI offset in seconds
  * @clock_was_set_seq:	The sequence number of clock was set events
  * @cs_was_changed_seq:	The sequence number of clocksource change events
···
 	ktime_t			offs_real;
 	ktime_t			offs_boot;
 	ktime_t			offs_tai;
-	ktime_t			time_suspended;
 	s32			tai_offset;
 	unsigned int		clock_was_set_seq;
 	u8			cs_was_changed_seq;

include/linux/timekeeping.h

···
 extern time64_t ktime_get_seconds(void);
 extern time64_t __ktime_get_real_seconds(void);
 extern time64_t ktime_get_real_seconds(void);
-extern void ktime_get_active_ts64(struct timespec64 *ts);
 
 extern int __getnstimeofday64(struct timespec64 *tv);
 extern void getnstimeofday64(struct timespec64 *tv);
 extern void getboottime64(struct timespec64 *ts);
 
-#define ktime_get_real_ts64(ts)		getnstimeofday64(ts)
-
-/* Clock BOOTTIME compatibility wrappers */
-static inline void get_monotonic_boottime64(struct timespec64 *ts)
-{
-	ktime_get_ts64(ts);
-}
+#define ktime_get_real_ts64(ts)	getnstimeofday64(ts)
 
 /*
  * ktime_t based interfaces
  */
+
 enum tk_offsets {
 	TK_OFFS_REAL,
+	TK_OFFS_BOOT,
 	TK_OFFS_TAI,
 	TK_OFFS_MAX,
 };
···
 extern ktime_t ktime_get_raw(void);
 extern u32 ktime_get_resolution_ns(void);
 
-/* Clock BOOTTIME compatibility wrappers */
-static inline ktime_t ktime_get_boottime(void) { return ktime_get(); }
-static inline u64 ktime_get_boot_ns(void) { return ktime_get(); }
-
 /**
  * ktime_get_real - get the real (wall-) time in ktime_t format
  */
 static inline ktime_t ktime_get_real(void)
 {
 	return ktime_get_with_offset(TK_OFFS_REAL);
+}
+
+/**
+ * ktime_get_boottime - Returns monotonic time since boot in ktime_t format
+ *
+ * This is similar to CLOCK_MONTONIC/ktime_get, but also includes the
+ * time spent in suspend.
+ */
+static inline ktime_t ktime_get_boottime(void)
+{
+	return ktime_get_with_offset(TK_OFFS_BOOT);
 }
 
 /**
···
 	return ktime_to_ns(ktime_get_real());
 }
 
+static inline u64 ktime_get_boot_ns(void)
+{
+	return ktime_to_ns(ktime_get_boottime());
+}
+
 static inline u64 ktime_get_tai_ns(void)
 {
 	return ktime_to_ns(ktime_get_clocktai());
···
 
 extern u64 ktime_get_mono_fast_ns(void);
 extern u64 ktime_get_raw_fast_ns(void);
+extern u64 ktime_get_boot_fast_ns(void);
 extern u64 ktime_get_real_fast_ns(void);
 
 /*
  * timespec64 interfaces utilizing the ktime based ones
  */
+static inline void get_monotonic_boottime64(struct timespec64 *ts)
+{
+	*ts = ktime_to_timespec64(ktime_get_boottime());
+}
+
 static inline void timekeeping_clocktai64(struct timespec64 *ts)
 {
 	*ts = ktime_to_timespec64(ktime_get_clocktai());

include/uapi/linux/time.h

···
  */
 #define CLOCK_SGI_CYCLE			10
 #define CLOCK_TAI			11
-#define CLOCK_MONOTONIC_ACTIVE		12
 
 #define MAX_CLOCKS			16
 #define CLOCKS_MASK			(CLOCK_REALTIME | CLOCK_MONOTONIC)

kernel/time/hrtimer.c

···
 			.get_time = &ktime_get_real,
 		},
 		{
+			.index = HRTIMER_BASE_BOOTTIME,
+			.clockid = CLOCK_BOOTTIME,
+			.get_time = &ktime_get_boottime,
+		},
+		{
 			.index = HRTIMER_BASE_TAI,
 			.clockid = CLOCK_TAI,
 			.get_time = &ktime_get_clocktai,
···
 			.get_time = &ktime_get_real,
 		},
 		{
+			.index = HRTIMER_BASE_BOOTTIME_SOFT,
+			.clockid = CLOCK_BOOTTIME,
+			.get_time = &ktime_get_boottime,
+		},
+		{
 			.index = HRTIMER_BASE_TAI_SOFT,
 			.clockid = CLOCK_TAI,
 			.get_time = &ktime_get_clocktai,
···
 
 	[CLOCK_REALTIME]	= HRTIMER_BASE_REALTIME,
 	[CLOCK_MONOTONIC]	= HRTIMER_BASE_MONOTONIC,
-	[CLOCK_BOOTTIME]	= HRTIMER_BASE_MONOTONIC,
+	[CLOCK_BOOTTIME]	= HRTIMER_BASE_BOOTTIME,
 	[CLOCK_TAI]		= HRTIMER_BASE_TAI,
 };
 
···
 static inline ktime_t hrtimer_update_base(struct hrtimer_cpu_base *base)
 {
 	ktime_t *offs_real = &base->clock_base[HRTIMER_BASE_REALTIME].offset;
+	ktime_t *offs_boot = &base->clock_base[HRTIMER_BASE_BOOTTIME].offset;
 	ktime_t *offs_tai = &base->clock_base[HRTIMER_BASE_TAI].offset;
 
 	ktime_t now = ktime_get_update_offsets_now(&base->clock_was_set_seq,
-						   offs_real, offs_tai);
+					    offs_real, offs_boot, offs_tai);
 
 	base->clock_base[HRTIMER_BASE_REALTIME_SOFT].offset = *offs_real;
+	base->clock_base[HRTIMER_BASE_BOOTTIME_SOFT].offset = *offs_boot;
 	base->clock_base[HRTIMER_BASE_TAI_SOFT].offset = *offs_tai;
 
 	return now;

kernel/time/posix-stubs.c

···
 	case CLOCK_BOOTTIME:
 		get_monotonic_boottime64(tp);
 		break;
-	case CLOCK_MONOTONIC_ACTIVE:
-		ktime_get_active_ts64(tp);
 	default:
 		return -EINVAL;
 	}

kernel/time/posix-timers.c

···
 	return 0;
 }
 
-static int posix_get_tai(clockid_t which_clock, struct timespec64 *tp)
+static int posix_get_boottime(const clockid_t which_clock, struct timespec64 *tp)
 {
-	timekeeping_clocktai64(tp);
+	get_monotonic_boottime64(tp);
 	return 0;
 }
 
-static int posix_get_monotonic_active(clockid_t which_clock,
-				      struct timespec64 *tp)
+static int posix_get_tai(clockid_t which_clock, struct timespec64 *tp)
 {
-	ktime_get_active_ts64(tp);
+	timekeeping_clocktai64(tp);
 	return 0;
 }
 
···
 	.timer_arm		= common_hrtimer_arm,
 };
 
-static const struct k_clock clock_monotonic_active = {
+static const struct k_clock clock_boottime = {
 	.clock_getres		= posix_get_hrtimer_res,
-	.clock_get		= posix_get_monotonic_active,
+	.clock_get		= posix_get_boottime,
+	.nsleep			= common_nsleep,
+	.timer_create		= common_timer_create,
+	.timer_set		= common_timer_set,
+	.timer_get		= common_timer_get,
+	.timer_del		= common_timer_del,
+	.timer_rearm		= common_hrtimer_rearm,
+	.timer_forward		= common_hrtimer_forward,
+	.timer_remaining	= common_hrtimer_remaining,
+	.timer_try_to_cancel	= common_hrtimer_try_to_cancel,
+	.timer_arm		= common_hrtimer_arm,
 };
 
 static const struct k_clock * const posix_clocks[] = {
···
 	[CLOCK_MONOTONIC_RAW]		= &clock_monotonic_raw,
 	[CLOCK_REALTIME_COARSE]		= &clock_realtime_coarse,
 	[CLOCK_MONOTONIC_COARSE]	= &clock_monotonic_coarse,
-	[CLOCK_BOOTTIME]		= &clock_monotonic,
+	[CLOCK_BOOTTIME]		= &clock_boottime,
 	[CLOCK_REALTIME_ALARM]		= &alarm_clock,
 	[CLOCK_BOOTTIME_ALARM]		= &alarm_clock,
 	[CLOCK_TAI]			= &clock_tai,
-	[CLOCK_MONOTONIC_ACTIVE]	= &clock_monotonic_active,
 };
 
 static const struct k_clock *clockid_to_kclock(const clockid_t id)

kernel/time/tick-common.c

···
 	clockevents_shutdown(td->evtdev);
 }
 
-static void tick_forward_next_period(void)
-{
-	ktime_t delta, now = ktime_get();
-	u64 n;
-
-	delta = ktime_sub(now, tick_next_period);
-	n = ktime_divns(delta, tick_period);
-	tick_next_period += n * tick_period;
-	if (tick_next_period < now)
-		tick_next_period += tick_period;
-	tick_sched_forward_next_period();
-}
-
 /**
  * tick_resume_local - Resume the local tick device
  *
···
 {
 	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
 	bool broadcast = tick_resume_check_broadcast();
-
-	tick_forward_next_period();
 
 	clockevents_tick_resume(td->evtdev);
 	if (!broadcast) {

kernel/time/tick-internal.h

···
 static inline bool tick_broadcast_oneshot_available(void) { return tick_oneshot_possible(); }
 #endif /* !(BROADCAST && ONESHOT) */
 
-#if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
-extern void tick_sched_forward_next_period(void);
-#else
-static inline void tick_sched_forward_next_period(void) { }
-#endif
-
 /* NO_HZ_FULL internal */
 #ifdef CONFIG_NO_HZ_FULL
 extern void tick_nohz_init(void);

kernel/time/tick-sched.c

···
 static ktime_t last_jiffies_update;
 
 /*
- * Called after resume. Make sure that jiffies are not fast forwarded due to
- * clock monotonic being forwarded by the suspended time.
- */
-void tick_sched_forward_next_period(void)
-{
-	last_jiffies_update = tick_next_period;
-}
-
-/*
  * Must be called with interrupts disabled !
  */
 static void tick_do_update_jiffies64(ktime_t now)

kernel/time/timekeeping.c

···
 
 static inline void tk_update_sleep_time(struct timekeeper *tk, ktime_t delta)
 {
-	/* Update both bases so mono and raw stay coupled. */
-	tk->tkr_mono.base += delta;
-	tk->tkr_raw.base += delta;
-
-	/* Accumulate time spent in suspend */
-	tk->time_suspended += delta;
+	tk->offs_boot = ktime_add(tk->offs_boot, delta);
 }
 
 /*
···
 }
 EXPORT_SYMBOL_GPL(ktime_get_raw_fast_ns);
 
+/**
+ * ktime_get_boot_fast_ns - NMI safe and fast access to boot clock.
+ *
+ * To keep it NMI safe since we're accessing from tracing, we're not using a
+ * separate timekeeper with updates to monotonic clock and boot offset
+ * protected with seqlocks. This has the following minor side effects:
+ *
+ * (1) Its possible that a timestamp be taken after the boot offset is updated
+ * but before the timekeeper is updated. If this happens, the new boot offset
+ * is added to the old timekeeping making the clock appear to update slightly
+ * earlier:
+ *    CPU 0                                        CPU 1
+ *    timekeeping_inject_sleeptime64()
+ *    __timekeeping_inject_sleeptime(tk, delta);
+ *                                                 timestamp();
+ *    timekeeping_update(tk, TK_CLEAR_NTP...);
+ *
+ * (2) On 32-bit systems, the 64-bit boot offset (tk->offs_boot) may be
+ * partially updated.  Since the tk->offs_boot update is a rare event, this
+ * should be a rare occurrence which postprocessing should be able to handle.
+ */
+u64 notrace ktime_get_boot_fast_ns(void)
+{
+	struct timekeeper *tk = &tk_core.timekeeper;
+
+	return (ktime_get_mono_fast_ns() + ktime_to_ns(tk->offs_boot));
+}
+EXPORT_SYMBOL_GPL(ktime_get_boot_fast_ns);
+
+
 /*
  * See comment for __ktime_get_fast_ns() vs. timestamp ordering
  */
···
 
 static ktime_t *offsets[TK_OFFS_MAX] = {
 	[TK_OFFS_REAL]	= &tk_core.timekeeper.offs_real,
+	[TK_OFFS_BOOT]	= &tk_core.timekeeper.offs_boot,
 	[TK_OFFS_TAI]	= &tk_core.timekeeper.offs_tai,
 };
 
···
 	timespec64_add_ns(ts, nsec + tomono.tv_nsec);
 }
 EXPORT_SYMBOL_GPL(ktime_get_ts64);
-
-/**
- * ktime_get_active_ts64 - Get the active non-suspended monotonic clock
- * @ts:		pointer to timespec variable
- *
- * The function calculates the monotonic clock from the realtime clock and
- * the wall_to_monotonic offset, subtracts the accumulated suspend time and
- * stores the result in normalized timespec64 format in the variable
- * pointed to by @ts.
- */
-void ktime_get_active_ts64(struct timespec64 *ts)
-{
-	struct timekeeper *tk = &tk_core.timekeeper;
-	struct timespec64 tomono, tsusp;
-	u64 nsec, nssusp;
-	unsigned int seq;
-
-	WARN_ON(timekeeping_suspended);
-
-	do {
-		seq = read_seqcount_begin(&tk_core.seq);
-		ts->tv_sec = tk->xtime_sec;
-		nsec = timekeeping_get_ns(&tk->tkr_mono);
-		tomono = tk->wall_to_monotonic;
-		nssusp = tk->time_suspended;
-	} while (read_seqcount_retry(&tk_core.seq, seq));
-
-	ts->tv_sec += tomono.tv_sec;
-	ts->tv_nsec = 0;
-	timespec64_add_ns(ts, nsec + tomono.tv_nsec);
-	tsusp = ns_to_timespec64(nssusp);
-	*ts = timespec64_sub(*ts, tsusp);
-}
 
 /**
  * ktime_get_seconds - Get the seconds portion of CLOCK_MONOTONIC
···
 		return;
 	}
 	tk_xtime_add(tk, delta);
+	tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, *delta));
 	tk_update_sleep_time(tk, timespec64_to_ktime(*delta));
 	tk_debug_account_sleep_time(delta);
 }
···
 void getboottime64(struct timespec64 *ts)
 {
 	struct timekeeper *tk = &tk_core.timekeeper;
-	ktime_t t = ktime_sub(tk->offs_real, tk->time_suspended);
+	ktime_t t = ktime_sub(tk->offs_real, tk->offs_boot);
 
 	*ts = ktime_to_timespec64(t);
 }
···
  * ktime_get_update_offsets_now - hrtimer helper
  * @cwsseq:	pointer to check and store the clock was set sequence number
  * @offs_real:	pointer to storage for monotonic -> realtime offset
+ * @offs_boot:	pointer to storage for monotonic -> boottime offset
  * @offs_tai:	pointer to storage for monotonic -> clock tai offset
  *
  * Returns current monotonic time and updates the offsets if the
···
  * Called from hrtimer_interrupt() or retrigger_next_event()
  */
 ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq, ktime_t *offs_real,
-				     ktime_t *offs_tai)
+				     ktime_t *offs_boot, ktime_t *offs_tai)
 {
 	struct timekeeper *tk = &tk_core.timekeeper;
 	unsigned int seq;
···
 		if (*cwsseq != tk->clock_was_set_seq) {
 			*cwsseq = tk->clock_was_set_seq;
 			*offs_real = tk->offs_real;
+			*offs_boot = tk->offs_boot;
 			*offs_tai = tk->offs_tai;
 		}
 

kernel/time/timekeeping.h

···
  */
 extern ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq,
 					    ktime_t *offs_real,
+					    ktime_t *offs_boot,
 					    ktime_t *offs_tai);
 
 extern int timekeeping_valid_for_hres(void);

kernel/trace/trace.c

···
 	{ trace_clock,			"perf",		1 },
 	{ ktime_get_mono_fast_ns,	"mono",		1 },
 	{ ktime_get_raw_fast_ns,	"mono_raw",	1 },
-	{ ktime_get_mono_fast_ns,	"boot",		1 },
+	{ ktime_get_boot_fast_ns,	"boot",		1 },
 	ARCH_TRACE_CLOCKS
 };