[PATCH v3 1/2] arch: um: pass nsecs to os timer functions

[PATCH v3 1/2] arch: um: pass nsecs to os timer functions

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

This makes the code clearer and lets the time travel patch have
the actual time used for these functions in just one place.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 arch/um/include/shared/os.h |  4 ++--
 arch/um/kernel/time.c       |  4 ++--
 arch/um/os-Linux/time.c     | 20 ++++++++------------
 3 files changed, 12 insertions(+), 16 deletions(-)

diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index 449e71edefaa..4a62ac4251a5 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -251,8 +251,8 @@ extern void os_warn(const char *fmt, ...)
 /* time.c */
 extern void os_idle_sleep(unsigned long long nsecs);
 extern int os_timer_create(void);
-extern int os_timer_set_interval(void);
-extern int os_timer_one_shot(unsigned long ticks);
+extern int os_timer_set_interval(unsigned long long nsecs);
+extern int os_timer_one_shot(unsigned long long nsecs);
 extern void os_timer_disable(void);
 extern void uml_idle_timer(void);
 extern long long os_persistent_clock_emulation(void);
diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c
index 3898119f773e..3a2fe54bef65 100644
--- a/arch/um/kernel/time.c
+++ b/arch/um/kernel/time.c
@@ -37,14 +37,14 @@ static int itimer_shutdown(struct clock_event_device *evt)
 
 static int itimer_set_periodic(struct clock_event_device *evt)
 {
-	os_timer_set_interval();
+	os_timer_set_interval(NSEC_PER_SEC / HZ);
 	return 0;
 }
 
 static int itimer_next_event(unsigned long delta,
 			     struct clock_event_device *evt)
 {
-	return os_timer_one_shot(delta);
+	return os_timer_one_shot(delta + 1);
 }
 
 static int itimer_one_shot(struct clock_event_device *evt)
diff --git a/arch/um/os-Linux/time.c b/arch/um/os-Linux/time.c
index ea720149f5b8..6d94ff52362c 100644
--- a/arch/um/os-Linux/time.c
+++ b/arch/um/os-Linux/time.c
@@ -50,18 +50,15 @@ int os_timer_create(void)
 	return 0;
 }
 
-int os_timer_set_interval(void)
+int os_timer_set_interval(unsigned long long nsecs)
 {
 	struct itimerspec its;
-	unsigned long long nsec;
 
-	nsec = UM_NSEC_PER_SEC / UM_HZ;
+	its.it_value.tv_sec = nsecs / UM_NSEC_PER_SEC;
+	its.it_value.tv_nsec = nsecs % UM_NSEC_PER_SEC;
 
-	its.it_value.tv_sec = 0;
-	its.it_value.tv_nsec = nsec;
-
-	its.it_interval.tv_sec = 0;
-	its.it_interval.tv_nsec = nsec;
+	its.it_interval.tv_sec = nsecs / UM_NSEC_PER_SEC;
+	its.it_interval.tv_nsec = nsecs % UM_NSEC_PER_SEC;
 
 	if (timer_settime(event_high_res_timer, 0, &its, NULL) == -1)
 		return -errno;
@@ -69,12 +66,11 @@ int os_timer_set_interval(void)
 	return 0;
 }
 
-int os_timer_one_shot(unsigned long ticks)
+int os_timer_one_shot(unsigned long long nsecs)
 {
-	unsigned long long nsec = ticks + 1;
 	struct itimerspec its = {
-		.it_value.tv_sec = nsec / UM_NSEC_PER_SEC,
-		.it_value.tv_nsec = nsec % UM_NSEC_PER_SEC,
+		.it_value.tv_sec = nsecs / UM_NSEC_PER_SEC,
+		.it_value.tv_nsec = nsecs % UM_NSEC_PER_SEC,
 
 		.it_interval.tv_sec = 0,
 		.it_interval.tv_nsec = 0, // we cheat here
-- 
2.17.2


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[PATCH v3 2/2] arch: um: support time travel mode

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

Sometimes it can be useful to run with "time travel" inside the
UML instance, for example for testing. For example, some tests
for the wireless subsystem and userspace are based on hwsim, a
virtual wireless adapter. Some tests can take a long time to
run because they e.g. wait for 120 seconds to elapse for some
regulatory checks. This obviously goes faster if it need not
actually wait that long, but time inside the test environment
just "bumps up" when there's nothing to do.

Add CONFIG_UML_TIME_TRAVEL_SUPPORT to enable code to support
such modes at runtime, selected on the command line:
 * just "time-travel", in which time inside the UML instance
   can move faster than real time, if there's nothing to do
 * "time-travel=inf-cpu" in which time also moves slower and
   any CPU processing takes no time at all, which allows to
   implement consistent behaviour regardless of host CPU load
   (or speed) or debug overhead.

An additional "time-travel-start=<seconds>" parameter is also
supported in this case to start the wall clock at this time
(in unix epoch).

With this enabled, the test mentioned above goes from a runtime
of about 140 seconds (with startup overhead and all) to being
CPU bound and finishing in 15 seconds (on my slow laptop).

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 arch/um/Kconfig                         |  12 +++
 arch/um/include/shared/timer-internal.h |  46 +++++++++
 arch/um/kernel/process.c                |  42 +++++++-
 arch/um/kernel/skas/syscall.c           |  11 ++
 arch/um/kernel/time.c                   | 129 ++++++++++++++++++++++--
 5 files changed, 233 insertions(+), 7 deletions(-)

diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index 07da2b284e46..14bb99c8039d 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -179,6 +179,18 @@ config SECCOMP
 
 	  If unsure, say Y.
 
+config UML_TIME_TRAVEL_SUPPORT
+	bool
+	prompt "Support time-travel mode (e.g. for test execution)"
+	help
+	  Enable this option to support time travel inside the UML instance.
+
+	  After enabling this option, two modes are accessible at runtime
+	  (selected by the kernel command line), see the kernel's command-
+	  line help for more details.
+
+	  It is safe to say Y, but you probably don't need this.
+
 endmenu
 
 source "arch/um/drivers/Kconfig"
diff --git a/arch/um/include/shared/timer-internal.h b/arch/um/include/shared/timer-internal.h
index 03e6f217f807..5ca74f415d52 100644
--- a/arch/um/include/shared/timer-internal.h
+++ b/arch/um/include/shared/timer-internal.h
@@ -10,4 +10,50 @@
 #define TIMER_MULTIPLIER 256
 #define TIMER_MIN_DELTA  500
 
+enum time_travel_mode {
+	TT_MODE_OFF,
+	TT_MODE_BASIC,
+	TT_MODE_INFCPU,
+};
+
+enum time_travel_timer_mode {
+	TT_TMR_DISABLED,
+	TT_TMR_ONESHOT,
+	TT_TMR_PERIODIC,
+};
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+extern enum time_travel_mode time_travel_mode;
+extern unsigned long long time_travel_time;
+extern enum time_travel_timer_mode time_travel_timer_mode;
+extern unsigned long long time_travel_timer_expiry;
+extern unsigned long long time_travel_timer_interval;
+
+static inline void time_travel_set_time(unsigned long long ns)
+{
+	time_travel_time = ns;
+}
+
+static inline void time_travel_set_timer(enum time_travel_timer_mode mode,
+					 unsigned long long expiry)
+{
+	time_travel_timer_mode = mode;
+	time_travel_timer_expiry = expiry;
+}
+#else
+#define time_travel_mode TT_MODE_OFF
+#define time_travel_time 0
+#define time_travel_timer_expiry 0
+#define time_travel_timer_interval 0
+
+static inline void time_travel_set_time(unsigned long long ns)
+{
+}
+
+static inline void time_travel_set_timer(enum time_travel_timer_mode mode,
+					 unsigned long long expiry)
+{
+}
+#endif
+
 #endif
diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index 691b83b10649..def2091697ca 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -203,10 +203,50 @@ void initial_thread_cb(void (*proc)(void *), void *arg)
 	kmalloc_ok = save_kmalloc_ok;
 }
 
+static void time_travel_sleep(unsigned long long duration)
+{
+	unsigned long long next = time_travel_time + duration;
+
+	if (time_travel_mode != TT_MODE_INFCPU)
+		os_timer_disable();
+
+	if (time_travel_timer_mode != TT_TMR_DISABLED ||
+	    time_travel_timer_expiry < next) {
+		if (time_travel_timer_mode == TT_TMR_ONESHOT)
+			time_travel_timer_mode = TT_TMR_DISABLED;
+		/*
+		 * time_travel_time will be adjusted in the timer
+		 * IRQ handler so it works even when the signal
+		 * comes from the OS timer
+		 */
+		deliver_alarm();
+	} else {
+		time_travel_set_time(next);
+	}
+
+	if (time_travel_mode != TT_MODE_INFCPU) {
+		if (time_travel_timer_mode == TT_TMR_PERIODIC)
+			os_timer_set_interval(time_travel_timer_interval);
+		else if (time_travel_timer_mode == TT_TMR_ONESHOT)
+			os_timer_one_shot(time_travel_timer_expiry - next);
+	}
+}
+
+static void um_idle_sleep(void)
+{
+	unsigned long long duration = UM_NSEC_PER_SEC;
+
+	if (time_travel_mode != TT_MODE_OFF) {
+		time_travel_sleep(duration);
+	} else {
+		os_idle_sleep(duration);
+	}
+}
+
 void arch_cpu_idle(void)
 {
 	cpu_tasks[current_thread_info()->cpu].pid = os_getpid();
-	os_idle_sleep(UM_NSEC_PER_SEC);
+	um_idle_sleep();
 	local_irq_enable();
 }
 
diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/syscall.c
index b783ac87d98a..44bb10785075 100644
--- a/arch/um/kernel/skas/syscall.c
+++ b/arch/um/kernel/skas/syscall.c
@@ -10,12 +10,23 @@
 #include <sysdep/ptrace.h>
 #include <sysdep/ptrace_user.h>
 #include <sysdep/syscalls.h>
+#include <shared/timer-internal.h>
 
 void handle_syscall(struct uml_pt_regs *r)
 {
 	struct pt_regs *regs = container_of(r, struct pt_regs, regs);
 	int syscall;
 
+	/*
+	 * If we have infinite CPU resources, then make every syscall also a
+	 * preemption point, since we don't have any other preemption in this
+	 * case, and kernel threads would basically never run until userspace
+	 * went to sleep, even if said userspace interacts with the kernel in
+	 * various ways.
+	 */
+	if (time_travel_mode == TT_MODE_INFCPU)
+		schedule();
+
 	/* Initialize the syscall number and default return value. */
 	UPT_SYSCALL_NR(r) = PT_SYSCALL_NR(r->gp);
 	PT_REGS_SET_SYSCALL_RETURN(regs, -ENOSYS);
diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c
index 3a2fe54bef65..6a051b078359 100644
--- a/arch/um/kernel/time.c
+++ b/arch/um/kernel/time.c
@@ -19,11 +19,29 @@
 #include <kern_util.h>
 #include <os.h>
 #include <timer-internal.h>
+#include <shared/init.h>
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+enum time_travel_mode time_travel_mode;
+unsigned long long time_travel_time;
+enum time_travel_timer_mode time_travel_timer_mode;
+unsigned long long time_travel_timer_expiry;
+unsigned long long time_travel_timer_interval;
+
+static bool time_travel_start_set;
+static unsigned long long time_travel_start;
+#else
+#define time_travel_start_set 0
+#define time_travel_start 0
+#endif
 
 void timer_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
 {
 	unsigned long flags;
 
+	if (time_travel_mode != TT_MODE_OFF)
+		time_travel_set_time(time_travel_timer_expiry);
+
 	local_irq_save(flags);
 	do_IRQ(TIMER_IRQ, regs);
 	local_irq_restore(flags);
@@ -31,26 +49,47 @@ void timer_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
 
 static int itimer_shutdown(struct clock_event_device *evt)
 {
-	os_timer_disable();
+	if (time_travel_mode != TT_MODE_OFF)
+		time_travel_set_timer(TT_TMR_DISABLED, 0);
+
+	if (time_travel_mode != TT_MODE_INFCPU)
+		os_timer_disable();
+
 	return 0;
 }
 
 static int itimer_set_periodic(struct clock_event_device *evt)
 {
-	os_timer_set_interval(NSEC_PER_SEC / HZ);
+	unsigned long long interval = NSEC_PER_SEC / HZ;
+
+	if (time_travel_mode != TT_MODE_OFF)
+		time_travel_set_timer(TT_TMR_PERIODIC,
+				      time_travel_time + interval);
+
+	if (time_travel_mode != TT_MODE_INFCPU)
+		os_timer_set_interval(interval);
+
 	return 0;
 }
 
 static int itimer_next_event(unsigned long delta,
 			     struct clock_event_device *evt)
 {
-	return os_timer_one_shot(delta + 1);
+	delta += 1;
+
+	if (time_travel_mode != TT_MODE_OFF)
+		time_travel_set_timer(TT_TMR_ONESHOT,
+				      time_travel_time + delta);
+
+	if (time_travel_mode != TT_MODE_INFCPU)
+		return os_timer_one_shot(delta);
+
+	return 0;
 }
 
 static int itimer_one_shot(struct clock_event_device *evt)
 {
-	os_timer_one_shot(1);
-	return 0;
+	return itimer_next_event(0, evt);
 }
 
 static struct clock_event_device timer_clockevent = {
@@ -87,6 +126,17 @@ static irqreturn_t um_timer(int irq, void *dev)
 
 static u64 timer_read(struct clocksource *cs)
 {
+	if (time_travel_mode != TT_MODE_OFF) {
+		/*
+		 * We make reading the timer cost a bit so that we don't get
+		 * stuck in loops that expect time to move more than the
+		 * exact requested sleep amount, e.g. python's socket server,
+		 * see https://bugs.python.org/issue37026.
+		 */
+		time_travel_set_time(time_travel_time + TIMER_MULTIPLIER);
+		return time_travel_time / TIMER_MULTIPLIER;
+	}
+
 	return os_nsecs() / TIMER_MULTIPLIER;
 }
 
@@ -123,7 +173,12 @@ static void __init um_timer_setup(void)
 
 void read_persistent_clock64(struct timespec64 *ts)
 {
-	long long nsecs = os_persistent_clock_emulation();
+	long long nsecs;
+
+	if (time_travel_start_set)
+		nsecs = time_travel_start + time_travel_time;
+	else
+		nsecs = os_persistent_clock_emulation();
 
 	set_normalized_timespec64(ts, nsecs / NSEC_PER_SEC,
 				  nsecs % NSEC_PER_SEC);
@@ -134,3 +189,65 @@ void __init time_init(void)
 	timer_set_signal_handler();
 	late_time_init = um_timer_setup;
 }
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+unsigned long calibrate_delay_is_known(void)
+{
+	if (time_travel_mode == TT_MODE_INFCPU)
+		return 1;
+	return 0;
+}
+
+int setup_time_travel(char *str)
+{
+	if (strcmp(str, "=inf-cpu") == 0) {
+		time_travel_mode = TT_MODE_INFCPU;
+		timer_clockevent.name = "time-travel-timer-infcpu";
+		timer_clocksource.name = "time-travel-clock";
+		return 1;
+	}
+
+	if (!*str) {
+		time_travel_mode = TT_MODE_BASIC;
+		timer_clockevent.name = "time-travel-timer";
+		timer_clocksource.name = "time-travel-clock";
+		return 1;
+	}
+
+	return -EINVAL;
+}
+
+__setup("time-travel", setup_time_travel);
+__uml_help(setup_time_travel,
+"time-travel\n"
+"This option just enables basic time travel mode, in which the clock/timers\n"
+"inside the UML instance skip forward when there's nothing to do, rather than\n"
+"waiting for real time to elapse. However, instance CPU speed is limited by\n"
+"the real CPU speed, so e.g. a 10ms timer will always fire after ~10ms wall\n"
+"clock (but quicker when there's nothing to do).\n"
+"\n"
+"time-travel=inf-cpu\n"
+"This enables time travel mode with infinite processing power, in which there\n"
+"are no wall clock timers, and any CPU processing happens - as seen from the\n"
+"guest - instantly. This can be useful for accurate simulation regardless of\n"
+"debug overhead, physical CPU speed, etc. but is somewhat dangerous as it can\n"
+"easily lead to getting stuck (e.g. if anything in the system busy loops).\n");
+
+int setup_time_travel_start(char *str)
+{
+	int err;
+
+	err = kstrtoull(str, 0, &time_travel_start);
+	if (err)
+		return err;
+
+	time_travel_start_set = 1;
+	return 1;
+}
+
+__setup("time-travel-start", setup_time_travel_start);
+__uml_help(setup_time_travel_start,
+"time-travel-start=<seconds>\n"
+"Configure the UML instance's wall clock to start at this value rather than\n"
+"the host's wall clock at the time of UML boot.\n");
+#endif
-- 
2.17.2


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Re: [PATCH v3 2/2] arch: um: support time travel mode

[Richard Weinberger]

----- Ursprüngliche Mail -----
> Von: "Johannes Berg" <johannes@sipsolutions.net>
> An: "linux-um" <linux-um@lists.infradead.org>
> CC: "Jeff Dike" <jdike@addtoit.com>, "richard" <richard@nod.at>, "anton ivanov" <anton.ivanov@cambridgegreys.com>,
> j@w1.fi, "Johannes Berg" <johannes.berg@intel.com>
> Gesendet: Montag, 27. Mai 2019 10:34:27
> Betreff: [PATCH v3 2/2] arch: um: support time travel mode

> From: Johannes Berg <johannes.berg@intel.com>
> 
> Sometimes it can be useful to run with "time travel" inside the
> UML instance, for example for testing. For example, some tests
> for the wireless subsystem and userspace are based on hwsim, a
> virtual wireless adapter. Some tests can take a long time to
> run because they e.g. wait for 120 seconds to elapse for some
> regulatory checks. This obviously goes faster if it need not
> actually wait that long, but time inside the test environment
> just "bumps up" when there's nothing to do.
> 
> Add CONFIG_UML_TIME_TRAVEL_SUPPORT to enable code to support
> such modes at runtime, selected on the command line:
> * just "time-travel", in which time inside the UML instance
>   can move faster than real time, if there's nothing to do
> * "time-travel=inf-cpu" in which time also moves slower and
>   any CPU processing takes no time at all, which allows to
>   implement consistent behaviour regardless of host CPU load
>   (or speed) or debug overhead.
> 
> An additional "time-travel-start=<seconds>" parameter is also
> supported in this case to start the wall clock at this time
> (in unix epoch).
> 
> With this enabled, the test mentioned above goes from a runtime
> of about 140 seconds (with startup overhead and all) to being
> CPU bound and finishing in 15 seconds (on my slow laptop).
> 
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>

This breaks the build for CONFIG_UML_TIME_TRAVEL_SUPPORT=n

What do you think about this followup fixup?
I committed your patch already to linux-next.
So, no need to resend. 

diff --git a/arch/um/include/shared/timer-internal.h b/arch/um/include/shared/timer-internal.h
index 5ca74f415d52..c15883b30c19 100644
--- a/arch/um/include/shared/timer-internal.h
+++ b/arch/um/include/shared/timer-internal.h
@@ -25,7 +25,7 @@ enum time_travel_timer_mode {
 #ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
 extern enum time_travel_mode time_travel_mode;
 extern unsigned long long time_travel_time;
-extern enum time_travel_timer_mode time_travel_timer_mode;
+extern enum time_travel_timer_mode tt_timer_mode;
 extern unsigned long long time_travel_timer_expiry;
 extern unsigned long long time_travel_timer_interval;
 
@@ -37,7 +37,7 @@ static inline void time_travel_set_time(unsigned long long ns)
 static inline void time_travel_set_timer(enum time_travel_timer_mode mode,
                                         unsigned long long expiry)
 {
-       time_travel_timer_mode = mode;
+       tt_timer_mode = mode;
        time_travel_timer_expiry = expiry;
 }
 #else
diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index def2091697ca..505408e2668d 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -205,15 +205,16 @@ void initial_thread_cb(void (*proc)(void *), void *arg)
 
 static void time_travel_sleep(unsigned long long duration)
 {
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
        unsigned long long next = time_travel_time + duration;
 
        if (time_travel_mode != TT_MODE_INFCPU)
                os_timer_disable();
 
-       if (time_travel_timer_mode != TT_TMR_DISABLED ||
+       if (tt_timer_mode != TT_TMR_DISABLED ||
            time_travel_timer_expiry < next) {
-               if (time_travel_timer_mode == TT_TMR_ONESHOT)
-                       time_travel_timer_mode = TT_TMR_DISABLED;
+               if (tt_timer_mode == TT_TMR_ONESHOT)
+                       tt_timer_mode = TT_TMR_DISABLED;
                /*
                 * time_travel_time will be adjusted in the timer
                 * IRQ handler so it works even when the signal
@@ -225,11 +226,12 @@ static void time_travel_sleep(unsigned long long duration)
        }
 
        if (time_travel_mode != TT_MODE_INFCPU) {
-               if (time_travel_timer_mode == TT_TMR_PERIODIC)
+               if (tt_timer_mode == TT_TMR_PERIODIC)
                        os_timer_set_interval(time_travel_timer_interval);
-               else if (time_travel_timer_mode == TT_TMR_ONESHOT)
+               else if (tt_timer_mode == TT_TMR_ONESHOT)
                        os_timer_one_shot(time_travel_timer_expiry - next);
        }
+#endif
 }
 
 static void um_idle_sleep(void)
diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c
index 6a051b078359..d27dd5bac0a6 100644
--- a/arch/um/kernel/time.c
+++ b/arch/um/kernel/time.c
@@ -24,7 +24,7 @@
 #ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
 enum time_travel_mode time_travel_mode;
 unsigned long long time_travel_time;
-enum time_travel_timer_mode time_travel_timer_mode;
+enum time_travel_timer_mode tt_timer_mode;
 unsigned long long time_travel_timer_expiry;
 unsigned long long time_travel_timer_interval;

Thanks,
//richard

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Re: [PATCH v3 2/2] arch: um: support time travel mode

[Johannes Berg]

On Tue, 2019-07-02 at 23:54 +0200, Richard Weinberger wrote:
> 
> This breaks the build for CONFIG_UML_TIME_TRAVEL_SUPPORT=n

D'oh. I was sure I tested that, but I guess not on the last version or
something... Sorry.

> What do you think about this followup fixup?
> I committed your patch already to linux-next.
> So, no need to resend. 
> 
> diff --git a/arch/um/include/shared/timer-internal.h b/arch/um/include/shared/timer-internal.h
> index 5ca74f415d52..c15883b30c19 100644
> --- a/arch/um/include/shared/timer-internal.h
> +++ b/arch/um/include/shared/timer-internal.h
> @@ -25,7 +25,7 @@ enum time_travel_timer_mode {
>  #ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
>  extern enum time_travel_mode time_travel_mode;
>  extern unsigned long long time_travel_time;
> -extern enum time_travel_timer_mode time_travel_timer_mode;
> +extern enum time_travel_timer_mode tt_timer_mode;
>  extern unsigned long long time_travel_timer_expiry;
>  extern unsigned long long time_travel_timer_interval;

Not sure renaming just this one makes sense (vs. the two others
above/below), but your call, I don't really care.

FWIW, my intent (after the comments wrt. ifdefs) had been to do it like
this:

diff --git a/arch/um/include/shared/timer-internal.h
b/arch/um/include/shared/timer-internal.h
index 5ca74f415d52..8574338bf23b 100644
--- a/arch/um/include/shared/timer-internal.h
+++ b/arch/um/include/shared/timer-internal.h
@@ -54,6 +54,8 @@ static inline void time_travel_set_timer(enum
time_travel_timer_mode mode,
 					 unsigned long long expiry)
 {
 }
+
+#define time_travel_timer_mode TT_TMR_DISABLED
 #endif
 
 #endif
diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index def2091697ca..67c0d1a860e9 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -213,7 +213,7 @@ static void time_travel_sleep(unsigned long long
duration)
 	if (time_travel_timer_mode != TT_TMR_DISABLED ||
 	    time_travel_timer_expiry < next) {
 		if (time_travel_timer_mode == TT_TMR_ONESHOT)
-			time_travel_timer_mode = TT_TMR_DISABLED;
+			time_travel_set_timer(TT_TMR_DISABLED, 0);
 		/*
 		 * time_travel_time will be adjusted in the timer
 		 * IRQ handler so it works even when the signal

johannes



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