[PATCH 0/3] rv: rtapp monitor update

[PATCH 0/3] rv: rtapp monitor update

[Nam Cao]

Hi,

A couple of minor improvements to the rtapp monitor, making the monitor
more informative to user and update the allow list regarding
clock_nanosleep syscall.

Nam Cao (3):
  rv/rtapp/sleep: Make the error more informative for user
  rv/rtapp/sleep: Update nanosleep rule
  rv/rtapp: Add wakeup monitor

 kernel/trace/rv/Kconfig                       |   1 +
 kernel/trace/rv/Makefile                      |   1 +
 kernel/trace/rv/monitors/sleep/sleep.c        |  18 +-
 kernel/trace/rv/monitors/sleep/sleep.h        |  52 +++---
 kernel/trace/rv/monitors/wakeup/Kconfig       |  17 ++
 kernel/trace/rv/monitors/wakeup/wakeup.c      | 155 ++++++++++++++++++
 kernel/trace/rv/monitors/wakeup/wakeup.h      |  92 +++++++++++
 .../trace/rv/monitors/wakeup/wakeup_trace.h   |  14 ++
 kernel/trace/rv/rv_trace.h                    |   1 +
 tools/verification/models/rtapp/sleep.ltl     |   2 +-
 tools/verification/models/rtapp/wakeup.ltl    |   5 +
 11 files changed, 318 insertions(+), 40 deletions(-)
 create mode 100644 kernel/trace/rv/monitors/wakeup/Kconfig
 create mode 100644 kernel/trace/rv/monitors/wakeup/wakeup.c
 create mode 100644 kernel/trace/rv/monitors/wakeup/wakeup.h
 create mode 100644 kernel/trace/rv/monitors/wakeup/wakeup_trace.h
 create mode 100644 tools/verification/models/rtapp/wakeup.ltl

-- 
2.47.3

[PATCH 1/3] rv/rtapp/sleep: Make the error more informative for user

[Nam Cao]

The rtapp/sleep monitor detects real-time tasks which go to sleep in an
real-time-unsafe manner. If this happen, the monitor triggers a trace event
in the sched_wakeup tracepoint's handler.

However, the invoking context of that trace event is not the most
informative, because of the stack trace of that event is the wakeup's code
path which is not very helpful:

74.669317: rv:error_sleep: condvar[254]: violation detected
    ltl_validate+0x345 ([kernel.kallsyms])
    handle_sched_wakeup+0x34 ([kernel.kallsyms])
    ttwu_do_activate+0xff ([kernel.kallsyms])
    sched_ttwu_pending+0x104 ([kernel.kallsyms])
    __flush_smp_call_function_queue+0x15b ([kernel.kallsyms])
    __sysvec_call_function_single+0x18 ([kernel.kallsyms])
    sysvec_call_function_single+0x66 ([kernel.kallsyms])
    asm_sysvec_call_function_single+0x1a ([kernel.kallsyms])
    pv_native_safe_halt+0xf ([kernel.kallsyms])
    default_idle+0x9 ([kernel.kallsyms])
    default_idle_call+0x33 ([kernel.kallsyms])
    do_idle+0x234 ([kernel.kallsyms])
    cpu_startup_entry+0x24 ([kernel.kallsyms])
    start_secondary+0xf8 ([kernel.kallsyms])
    common_startup_64+0x13e ([kernel.kallsyms])

What would be much more valuable is the stack trace of the task itself.

Change the update of WAKEUP from being in sched_wakeup trace point's
handler to sched_exit trace point's handler. This makes the event happen in
the task's context, making the stack trace far more informative for user:

rv:error_sleep: condvar[254]: violation detected
    ltl_validate+0x345 ([kernel.kallsyms])
    handle_sched_exit+0x39 ([kernel.kallsyms])
    __schedule+0x80f ([kernel.kallsyms])
    schedule+0x22 ([kernel.kallsyms])
    futex_do_wait+0x33 ([kernel.kallsyms])
    __futex_wait+0x8c ([kernel.kallsyms])
    futex_wait+0x73 ([kernel.kallsyms])
    do_futex+0xc6 ([kernel.kallsyms])
    __x64_sys_futex+0x121 ([kernel.kallsyms])
    do_syscall_64+0xf3 ([kernel.kallsyms])
    entry_SYSCALL_64_after_hwframe+0x77 ([kernel.kallsyms])
    __futex_abstimed_wait_common64+0xc6 (inlined)
    __futex_abstimed_wait_common+0xc6 (/usr/lib/x86_64-linux-gnu/libc.so.6)

Signed-off-by: Nam Cao <namcao@linutronix.de>
---
 kernel/trace/rv/monitors/sleep/sleep.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/rv/monitors/sleep/sleep.c b/kernel/trace/rv/monitors/sleep/sleep.c
index 8dfe5ec13e19..0a36f5519e6b 100644
--- a/kernel/trace/rv/monitors/sleep/sleep.c
+++ b/kernel/trace/rv/monitors/sleep/sleep.c
@@ -92,9 +92,9 @@ static void handle_sched_set_state(void *data, struct task_struct *task, int sta
 		ltl_atom_pulse(task, LTL_ABORT_SLEEP, true);
 }
 
-static void handle_sched_wakeup(void *data, struct task_struct *task)
+static void handle_sched_exit(void *data, bool is_switch)
 {
-	ltl_atom_pulse(task, LTL_WAKE, true);
+	ltl_atom_pulse(current, LTL_WAKE, true);
 }
 
 static void handle_sched_waking(void *data, struct task_struct *task)
@@ -200,7 +200,7 @@ static int enable_sleep(void)
 		return retval;
 
 	rv_attach_trace_probe("rtapp_sleep", sched_waking, handle_sched_waking);
-	rv_attach_trace_probe("rtapp_sleep", sched_wakeup, handle_sched_wakeup);
+	rv_attach_trace_probe("rtapp_sleep", sched_exit_tp, handle_sched_exit);
 	rv_attach_trace_probe("rtapp_sleep", sched_set_state_tp, handle_sched_set_state);
 	rv_attach_trace_probe("rtapp_sleep", contention_begin, handle_contention_begin);
 	rv_attach_trace_probe("rtapp_sleep", contention_end, handle_contention_end);
@@ -213,7 +213,7 @@ static int enable_sleep(void)
 static void disable_sleep(void)
 {
 	rv_detach_trace_probe("rtapp_sleep", sched_waking, handle_sched_waking);
-	rv_detach_trace_probe("rtapp_sleep", sched_wakeup, handle_sched_wakeup);
+	rv_detach_trace_probe("rtapp_sleep", sched_exit_tp, handle_sched_exit);
 	rv_detach_trace_probe("rtapp_sleep", sched_set_state_tp, handle_sched_set_state);
 	rv_detach_trace_probe("rtapp_sleep", contention_begin, handle_contention_begin);
 	rv_detach_trace_probe("rtapp_sleep", contention_end, handle_contention_end);
-- 
2.47.3

[PATCH 2/3] rv/rtapp/sleep: Update nanosleep rule

[Nam Cao]

CLOCK_REALTIME is the only clock that often is misused in real-time
applications. The other clocks either are safe for real-time uses
(CLOCK_TAI, CLOCK_MONOTONIC, CLOCK_BOOTTIME) or are unlikely to be misused
(CLOCK_AUX, CLOCK_PROCESS_CPUTIME_ID).

The rtapp monitor's purpose is warning people about common mistakes with
real-time design. However, warning about all clock types generates too much
false positives.

Update the monitor to only warn about CLOCK_REALTIME.

Signed-off-by: Nam Cao <namcao@linutronix.de>
---
 kernel/trace/rv/monitors/sleep/sleep.c    | 10 ++---
 kernel/trace/rv/monitors/sleep/sleep.h    | 52 +++++++++++------------
 tools/verification/models/rtapp/sleep.ltl |  2 +-
 3 files changed, 28 insertions(+), 36 deletions(-)

diff --git a/kernel/trace/rv/monitors/sleep/sleep.c b/kernel/trace/rv/monitors/sleep/sleep.c
index 0a36f5519e6b..e01ac56b3f4a 100644
--- a/kernel/trace/rv/monitors/sleep/sleep.c
+++ b/kernel/trace/rv/monitors/sleep/sleep.c
@@ -43,9 +43,7 @@ static void ltl_atoms_init(struct task_struct *task, struct ltl_monitor *mon, bo
 	ltl_atom_set(mon, LTL_WOKEN_BY_EQUAL_OR_HIGHER_PRIO, false);
 
 	if (task_creation) {
-		ltl_atom_set(mon, LTL_KTHREAD_SHOULD_STOP, false);
-		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_MONOTONIC, false);
-		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_TAI, false);
+		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_REALTIME, false);
 		ltl_atom_set(mon, LTL_NANOSLEEP_TIMER_ABSTIME, false);
 		ltl_atom_set(mon, LTL_CLOCK_NANOSLEEP, false);
 		ltl_atom_set(mon, LTL_FUTEX_WAIT, false);
@@ -136,8 +134,7 @@ static void handle_sys_enter(void *data, struct pt_regs *regs, long id)
 	case __NR_clock_nanosleep_time64:
 #endif
 		syscall_get_arguments(current, regs, args);
-		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_MONOTONIC, args[0] == CLOCK_MONOTONIC);
-		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_TAI, args[0] == CLOCK_TAI);
+		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_REALTIME, args[0] == CLOCK_REALTIME);
 		ltl_atom_set(mon, LTL_NANOSLEEP_TIMER_ABSTIME, args[1] == TIMER_ABSTIME);
 		ltl_atom_update(current, LTL_CLOCK_NANOSLEEP, true);
 		break;
@@ -178,8 +175,7 @@ static void handle_sys_exit(void *data, struct pt_regs *regs, long ret)
 
 	ltl_atom_set(mon, LTL_FUTEX_LOCK_PI, false);
 	ltl_atom_set(mon, LTL_FUTEX_WAIT, false);
-	ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_MONOTONIC, false);
-	ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_TAI, false);
+	ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_REALTIME, false);
 	ltl_atom_set(mon, LTL_NANOSLEEP_TIMER_ABSTIME, false);
 	ltl_atom_set(mon, LTL_EPOLL_WAIT, false);
 	ltl_atom_update(current, LTL_CLOCK_NANOSLEEP, false);
diff --git a/kernel/trace/rv/monitors/sleep/sleep.h b/kernel/trace/rv/monitors/sleep/sleep.h
index 95dc2727c059..ed1ac7ad008e 100644
--- a/kernel/trace/rv/monitors/sleep/sleep.h
+++ b/kernel/trace/rv/monitors/sleep/sleep.h
@@ -20,8 +20,7 @@ enum ltl_atom {
 	LTL_FUTEX_WAIT,
 	LTL_KERNEL_THREAD,
 	LTL_KTHREAD_SHOULD_STOP,
-	LTL_NANOSLEEP_CLOCK_MONOTONIC,
-	LTL_NANOSLEEP_CLOCK_TAI,
+	LTL_NANOSLEEP_CLOCK_REALTIME,
 	LTL_NANOSLEEP_TIMER_ABSTIME,
 	LTL_RT,
 	LTL_SLEEP,
@@ -46,8 +45,7 @@ static const char *ltl_atom_str(enum ltl_atom atom)
 		"fu_wa",
 		"ker_th",
 		"kth_sh_st",
-		"na_cl_mo",
-		"na_cl_ta",
+		"na_cl_re",
 		"na_ti_ab",
 		"rt",
 		"sl",
@@ -87,8 +85,7 @@ static void ltl_start(struct task_struct *task, struct ltl_monitor *mon)
 	bool sleep = test_bit(LTL_SLEEP, mon->atoms);
 	bool rt = test_bit(LTL_RT, mon->atoms);
 	bool nanosleep_timer_abstime = test_bit(LTL_NANOSLEEP_TIMER_ABSTIME, mon->atoms);
-	bool nanosleep_clock_tai = test_bit(LTL_NANOSLEEP_CLOCK_TAI, mon->atoms);
-	bool nanosleep_clock_monotonic = test_bit(LTL_NANOSLEEP_CLOCK_MONOTONIC, mon->atoms);
+	bool nanosleep_clock_realtime = test_bit(LTL_NANOSLEEP_CLOCK_REALTIME, mon->atoms);
 	bool kthread_should_stop = test_bit(LTL_KTHREAD_SHOULD_STOP, mon->atoms);
 	bool kernel_thread = test_bit(LTL_KERNEL_THREAD, mon->atoms);
 	bool futex_wait = test_bit(LTL_FUTEX_WAIT, mon->atoms);
@@ -97,17 +94,17 @@ static void ltl_start(struct task_struct *task, struct ltl_monitor *mon)
 	bool clock_nanosleep = test_bit(LTL_CLOCK_NANOSLEEP, mon->atoms);
 	bool block_on_rt_mutex = test_bit(LTL_BLOCK_ON_RT_MUTEX, mon->atoms);
 	bool abort_sleep = test_bit(LTL_ABORT_SLEEP, mon->atoms);
-	bool val42 = task_is_rcu || task_is_migration;
-	bool val43 = futex_lock_pi || val42;
-	bool val5 = block_on_rt_mutex || val43;
-	bool val34 = abort_sleep || kthread_should_stop;
-	bool val35 = woken_by_nmi || val34;
-	bool val36 = woken_by_hardirq || val35;
-	bool val14 = woken_by_equal_or_higher_prio || val36;
+	bool val41 = task_is_rcu || task_is_migration;
+	bool val42 = futex_lock_pi || val41;
+	bool val5 = block_on_rt_mutex || val42;
+	bool val33 = abort_sleep || kthread_should_stop;
+	bool val34 = woken_by_nmi || val33;
+	bool val35 = woken_by_hardirq || val34;
+	bool val14 = woken_by_equal_or_higher_prio || val35;
 	bool val13 = !wake;
-	bool val26 = nanosleep_clock_monotonic || nanosleep_clock_tai;
-	bool val27 = nanosleep_timer_abstime && val26;
-	bool val18 = clock_nanosleep && val27;
+	bool val25 = !nanosleep_clock_realtime;
+	bool val26 = nanosleep_timer_abstime && val25;
+	bool val18 = clock_nanosleep && val26;
 	bool val20 = val18 || epoll_wait;
 	bool val9 = futex_wait || val20;
 	bool val11 = val9 || kernel_thread;
@@ -138,8 +135,7 @@ ltl_possible_next_states(struct ltl_monitor *mon, unsigned int state, unsigned l
 	bool sleep = test_bit(LTL_SLEEP, mon->atoms);
 	bool rt = test_bit(LTL_RT, mon->atoms);
 	bool nanosleep_timer_abstime = test_bit(LTL_NANOSLEEP_TIMER_ABSTIME, mon->atoms);
-	bool nanosleep_clock_tai = test_bit(LTL_NANOSLEEP_CLOCK_TAI, mon->atoms);
-	bool nanosleep_clock_monotonic = test_bit(LTL_NANOSLEEP_CLOCK_MONOTONIC, mon->atoms);
+	bool nanosleep_clock_realtime = test_bit(LTL_NANOSLEEP_CLOCK_REALTIME, mon->atoms);
 	bool kthread_should_stop = test_bit(LTL_KTHREAD_SHOULD_STOP, mon->atoms);
 	bool kernel_thread = test_bit(LTL_KERNEL_THREAD, mon->atoms);
 	bool futex_wait = test_bit(LTL_FUTEX_WAIT, mon->atoms);
@@ -148,17 +144,17 @@ ltl_possible_next_states(struct ltl_monitor *mon, unsigned int state, unsigned l
 	bool clock_nanosleep = test_bit(LTL_CLOCK_NANOSLEEP, mon->atoms);
 	bool block_on_rt_mutex = test_bit(LTL_BLOCK_ON_RT_MUTEX, mon->atoms);
 	bool abort_sleep = test_bit(LTL_ABORT_SLEEP, mon->atoms);
-	bool val42 = task_is_rcu || task_is_migration;
-	bool val43 = futex_lock_pi || val42;
-	bool val5 = block_on_rt_mutex || val43;
-	bool val34 = abort_sleep || kthread_should_stop;
-	bool val35 = woken_by_nmi || val34;
-	bool val36 = woken_by_hardirq || val35;
-	bool val14 = woken_by_equal_or_higher_prio || val36;
+	bool val41 = task_is_rcu || task_is_migration;
+	bool val42 = futex_lock_pi || val41;
+	bool val5 = block_on_rt_mutex || val42;
+	bool val33 = abort_sleep || kthread_should_stop;
+	bool val34 = woken_by_nmi || val33;
+	bool val35 = woken_by_hardirq || val34;
+	bool val14 = woken_by_equal_or_higher_prio || val35;
 	bool val13 = !wake;
-	bool val26 = nanosleep_clock_monotonic || nanosleep_clock_tai;
-	bool val27 = nanosleep_timer_abstime && val26;
-	bool val18 = clock_nanosleep && val27;
+	bool val25 = !nanosleep_clock_realtime;
+	bool val26 = nanosleep_timer_abstime && val25;
+	bool val18 = clock_nanosleep && val26;
 	bool val20 = val18 || epoll_wait;
 	bool val9 = futex_wait || val20;
 	bool val11 = val9 || kernel_thread;
diff --git a/tools/verification/models/rtapp/sleep.ltl b/tools/verification/models/rtapp/sleep.ltl
index 6f26c4810f78..2637bc48a620 100644
--- a/tools/verification/models/rtapp/sleep.ltl
+++ b/tools/verification/models/rtapp/sleep.ltl
@@ -9,7 +9,7 @@ RT_VALID_SLEEP_REASON = FUTEX_WAIT
 
 RT_FRIENDLY_NANOSLEEP = CLOCK_NANOSLEEP
                     and NANOSLEEP_TIMER_ABSTIME
-                    and (NANOSLEEP_CLOCK_MONOTONIC or NANOSLEEP_CLOCK_TAI)
+                    and not NANOSLEEP_CLOCK_REALTIME
 
 RT_FRIENDLY_WAKE = WOKEN_BY_EQUAL_OR_HIGHER_PRIO
                 or WOKEN_BY_HARDIRQ
-- 
2.47.3

[PATCH 3/3] rv/rtapp: Add wakeup monitor

[Nam Cao]

Add a wakeup monitor to detect a lower-priority task waking up a
higher-priority task.

The rtapp/sleep monitor already detects this. However, that monitor
triggers an error in the context of the woken task and user only gets the
stacktrace of that task. It is also extremely useful to get the stacktrace
of the waking task, which this monitor offers. In other words, this monitor
complements the rtapp/sleep monitor.

Signed-off-by: Nam Cao <namcao@linutronix.de>
---
 kernel/trace/rv/Kconfig                       |   1 +
 kernel/trace/rv/Makefile                      |   1 +
 kernel/trace/rv/monitors/wakeup/Kconfig       |  17 ++
 kernel/trace/rv/monitors/wakeup/wakeup.c      | 155 ++++++++++++++++++
 kernel/trace/rv/monitors/wakeup/wakeup.h      |  92 +++++++++++
 .../trace/rv/monitors/wakeup/wakeup_trace.h   |  14 ++
 kernel/trace/rv/rv_trace.h                    |   1 +
 tools/verification/models/rtapp/wakeup.ltl    |   5 +
 8 files changed, 286 insertions(+)
 create mode 100644 kernel/trace/rv/monitors/wakeup/Kconfig
 create mode 100644 kernel/trace/rv/monitors/wakeup/wakeup.c
 create mode 100644 kernel/trace/rv/monitors/wakeup/wakeup.h
 create mode 100644 kernel/trace/rv/monitors/wakeup/wakeup_trace.h
 create mode 100644 tools/verification/models/rtapp/wakeup.ltl

diff --git a/kernel/trace/rv/Kconfig b/kernel/trace/rv/Kconfig
index 3884b14df375..4d3a14a0bac2 100644
--- a/kernel/trace/rv/Kconfig
+++ b/kernel/trace/rv/Kconfig
@@ -76,6 +76,7 @@ source "kernel/trace/rv/monitors/opid/Kconfig"
 source "kernel/trace/rv/monitors/rtapp/Kconfig"
 source "kernel/trace/rv/monitors/pagefault/Kconfig"
 source "kernel/trace/rv/monitors/sleep/Kconfig"
+source "kernel/trace/rv/monitors/wakeup/Kconfig"
 # Add new rtapp monitors here
 
 source "kernel/trace/rv/monitors/stall/Kconfig"
diff --git a/kernel/trace/rv/Makefile b/kernel/trace/rv/Makefile
index 94498da35b37..c2c0e4142eb4 100644
--- a/kernel/trace/rv/Makefile
+++ b/kernel/trace/rv/Makefile
@@ -20,6 +20,7 @@ obj-$(CONFIG_RV_MON_OPID) += monitors/opid/opid.o
 obj-$(CONFIG_RV_MON_STALL) += monitors/stall/stall.o
 obj-$(CONFIG_RV_MON_DEADLINE) += monitors/deadline/deadline.o
 obj-$(CONFIG_RV_MON_NOMISS) += monitors/nomiss/nomiss.o
+obj-$(CONFIG_RV_MON_WAKEUP) += monitors/wakeup/wakeup.o
 # Add new monitors here
 obj-$(CONFIG_RV_REACTORS) += rv_reactors.o
 obj-$(CONFIG_RV_REACT_PRINTK) += reactor_printk.o
diff --git a/kernel/trace/rv/monitors/wakeup/Kconfig b/kernel/trace/rv/monitors/wakeup/Kconfig
new file mode 100644
index 000000000000..3cf11c5cd5f7
--- /dev/null
+++ b/kernel/trace/rv/monitors/wakeup/Kconfig
@@ -0,0 +1,17 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+config RV_MON_WAKEUP
+	depends on RV
+	depends on RV_MON_RTAPP
+	depends on HAVE_SYSCALL_TRACEPOINTS
+	select TRACE_IRQFLAGS
+	default y
+	select LTL_MON_EVENTS_ID
+	bool "wakeup monitor"
+	help
+	  This monitor detects a lower-priority task waking up a
+	  higher-priority task. The RV_MON_SLEEP monitor already
+	  detects this case, but this monitor detects in the context
+	  of the waking task instead. This and RV_MON_SLEEP can be
+	  enabled together to get the stacktrace of both the waking
+	  task and the woken task.
diff --git a/kernel/trace/rv/monitors/wakeup/wakeup.c b/kernel/trace/rv/monitors/wakeup/wakeup.c
new file mode 100644
index 000000000000..534997a7b45c
--- /dev/null
+++ b/kernel/trace/rv/monitors/wakeup/wakeup.c
@@ -0,0 +1,155 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/ftrace.h>
+#include <linux/tracepoint.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/rv.h>
+#include <rv/instrumentation.h>
+
+#define MODULE_NAME "wakeup"
+
+#include <trace/events/syscalls.h>
+#include <trace/events/sched.h>
+#include <trace/events/lock.h>
+#include <uapi/linux/futex.h>
+
+#include <rv_trace.h>
+#include <monitors/rtapp/rtapp.h>
+
+
+#ifndef __NR_futex
+#define __NR_futex (-__COUNTER__)
+#endif
+#ifndef __NR_futex_time64
+#define __NR_futex_time64 (-__COUNTER__)
+#endif
+
+#include "wakeup.h"
+#include <rv/ltl_monitor.h>
+
+static void ltl_atoms_fetch(struct task_struct *task, struct ltl_monitor *mon)
+{
+	/*
+	 * This includes "actual" real-time tasks and also PI-boosted
+	 * tasks. A task being PI-boosted means it is blocking an "actual"
+	 * real-task, therefore it should also obey the monitor's rule,
+	 * otherwise the "actual" real-task may be delayed.
+	 */
+	ltl_atom_set(mon, LTL_RT, rt_or_dl_task(task));
+}
+
+static void ltl_atoms_init(struct task_struct *task, struct ltl_monitor *mon, bool task_creation)
+{
+	ltl_atom_set(mon, LTL_WOKEN_BY_LOWER_PRIO, false);
+	ltl_atom_set(mon, LTL_WOKEN_BY_SOFTIRQ, false);
+
+	if (task_creation) {
+		ltl_atom_set(mon, LTL_BLOCK_ON_RT_MUTEX, false);
+		ltl_atom_set(mon, LTL_FUTEX_LOCK_PI, false);
+	}
+
+	ltl_atom_set(mon, LTL_USER_THREAD, !(task->flags & PF_KTHREAD));
+}
+
+static void handle_sched_waking(void *data, struct task_struct *task)
+{
+	if (this_cpu_read(hardirq_context)) {
+		return;
+	} else if (in_task()) {
+		if (current->prio > task->prio)
+			ltl_atom_pulse(task, LTL_WOKEN_BY_LOWER_PRIO, true);
+	} else if (in_serving_softirq()) {
+		ltl_atom_pulse(task, LTL_WOKEN_BY_SOFTIRQ, true);
+	}
+}
+
+static void handle_contention_begin(void *data, void *lock, unsigned int flags)
+{
+	if (flags & LCB_F_RT)
+		ltl_atom_update(current, LTL_BLOCK_ON_RT_MUTEX, true);
+}
+
+static void handle_contention_end(void *data, void *lock, int ret)
+{
+	ltl_atom_update(current, LTL_BLOCK_ON_RT_MUTEX, false);
+}
+
+static void handle_sys_enter(void *data, struct pt_regs *regs, long id)
+{
+	unsigned long args[6];
+	int op, cmd;
+
+	switch (id) {
+	case __NR_futex:
+	case __NR_futex_time64:
+		syscall_get_arguments(current, regs, args);
+		op = args[1];
+		cmd = op & FUTEX_CMD_MASK;
+
+		switch (cmd) {
+		case FUTEX_LOCK_PI:
+		case FUTEX_LOCK_PI2:
+			ltl_atom_update(current, LTL_FUTEX_LOCK_PI, true);
+			break;
+		}
+		break;
+	}
+}
+
+static void handle_sys_exit(void *data, struct pt_regs *regs, long ret)
+{
+	ltl_atom_update(current, LTL_FUTEX_LOCK_PI, false);
+}
+
+static int enable_wakeup(void)
+{
+	int retval;
+
+	retval = ltl_monitor_init();
+	if (retval)
+		return retval;
+
+	rv_attach_trace_probe("rtapp_wakeup", sched_waking, handle_sched_waking);
+	rv_attach_trace_probe("rtapp_wakeup", contention_begin, handle_contention_begin);
+	rv_attach_trace_probe("rtapp_wakeup", contention_end, handle_contention_end);
+	rv_attach_trace_probe("rtapp_wakeup", sys_enter, handle_sys_enter);
+	rv_attach_trace_probe("rtapp_wakeup", sys_exit, handle_sys_exit);
+
+	return 0;
+}
+
+static void disable_wakeup(void)
+{
+	rv_detach_trace_probe("rtapp_wakeup", sched_waking, handle_sched_waking);
+	rv_detach_trace_probe("rtapp_wakeup", contention_begin, handle_contention_begin);
+	rv_detach_trace_probe("rtapp_wakeup", contention_end, handle_contention_end);
+	rv_detach_trace_probe("rtapp_wakeup", sys_enter, handle_sys_enter);
+	rv_detach_trace_probe("rtapp_wakeup", sys_exit, handle_sys_exit);
+
+	ltl_monitor_destroy();
+}
+
+static struct rv_monitor rv_wakeup = {
+	.name = "wakeup",
+	.description = "Monitor that real-time tasks are not woken by lower-priority tasks",
+	.enable = enable_wakeup,
+	.disable = disable_wakeup,
+};
+
+static int __init register_wakeup(void)
+{
+	return rv_register_monitor(&rv_wakeup, &rv_rtapp);
+}
+
+static void __exit unregister_wakeup(void)
+{
+	rv_unregister_monitor(&rv_wakeup);
+}
+
+module_init(register_wakeup);
+module_exit(unregister_wakeup);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Nam Cao <namcao@linutronix.de>");
+MODULE_DESCRIPTION("Monitor that real-time tasks are not woken by lower-priority tasks");
diff --git a/kernel/trace/rv/monitors/wakeup/wakeup.h b/kernel/trace/rv/monitors/wakeup/wakeup.h
new file mode 100644
index 000000000000..6f80da64e0e1
--- /dev/null
+++ b/kernel/trace/rv/monitors/wakeup/wakeup.h
@@ -0,0 +1,92 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * C implementation of Buchi automaton, automatically generated by
+ * tools/verification/rvgen from the linear temporal logic specification.
+ * For further information, see kernel documentation:
+ *   Documentation/trace/rv/linear_temporal_logic.rst
+ */
+
+#include <linux/rv.h>
+
+#define MONITOR_NAME wakeup
+
+enum ltl_atom {
+	LTL_BLOCK_ON_RT_MUTEX,
+	LTL_FUTEX_LOCK_PI,
+	LTL_RT,
+	LTL_USER_THREAD,
+	LTL_WOKEN_BY_LOWER_PRIO,
+	LTL_WOKEN_BY_SOFTIRQ,
+	LTL_NUM_ATOM
+};
+static_assert(LTL_NUM_ATOM <= RV_MAX_LTL_ATOM);
+
+static const char *ltl_atom_str(enum ltl_atom atom)
+{
+	static const char *const names[] = {
+		"bl_on_rt_mu",
+		"fu_lo_pi",
+		"rt",
+		"us_th",
+		"wo_lo_pr",
+		"wo_so",
+	};
+
+	return names[atom];
+}
+
+enum ltl_buchi_state {
+	S0,
+	RV_NUM_BA_STATES
+};
+static_assert(RV_NUM_BA_STATES <= RV_MAX_BA_STATES);
+
+static void ltl_start(struct task_struct *task, struct ltl_monitor *mon)
+{
+	bool woken_by_softirq = test_bit(LTL_WOKEN_BY_SOFTIRQ, mon->atoms);
+	bool woken_by_lower_prio = test_bit(LTL_WOKEN_BY_LOWER_PRIO, mon->atoms);
+	bool user_thread = test_bit(LTL_USER_THREAD, mon->atoms);
+	bool rt = test_bit(LTL_RT, mon->atoms);
+	bool futex_lock_pi = test_bit(LTL_FUTEX_LOCK_PI, mon->atoms);
+	bool block_on_rt_mutex = test_bit(LTL_BLOCK_ON_RT_MUTEX, mon->atoms);
+	bool val9 = block_on_rt_mutex || futex_lock_pi;
+	bool val6 = !woken_by_softirq;
+	bool val5 = !woken_by_lower_prio;
+	bool val8 = val5 && val6;
+	bool val10 = val8 || val9;
+	bool val3 = !user_thread;
+	bool val2 = !rt;
+	bool val4 = val2 || val3;
+	bool val11 = val4 || val10;
+
+	if (val11)
+		__set_bit(S0, mon->states);
+}
+
+static void
+ltl_possible_next_states(struct ltl_monitor *mon, unsigned int state, unsigned long *next)
+{
+	bool woken_by_softirq = test_bit(LTL_WOKEN_BY_SOFTIRQ, mon->atoms);
+	bool woken_by_lower_prio = test_bit(LTL_WOKEN_BY_LOWER_PRIO, mon->atoms);
+	bool user_thread = test_bit(LTL_USER_THREAD, mon->atoms);
+	bool rt = test_bit(LTL_RT, mon->atoms);
+	bool futex_lock_pi = test_bit(LTL_FUTEX_LOCK_PI, mon->atoms);
+	bool block_on_rt_mutex = test_bit(LTL_BLOCK_ON_RT_MUTEX, mon->atoms);
+	bool val9 = block_on_rt_mutex || futex_lock_pi;
+	bool val6 = !woken_by_softirq;
+	bool val5 = !woken_by_lower_prio;
+	bool val8 = val5 && val6;
+	bool val10 = val8 || val9;
+	bool val3 = !user_thread;
+	bool val2 = !rt;
+	bool val4 = val2 || val3;
+	bool val11 = val4 || val10;
+
+	switch (state) {
+	case S0:
+		if (val11)
+			__set_bit(S0, next);
+		break;
+	}
+}
diff --git a/kernel/trace/rv/monitors/wakeup/wakeup_trace.h b/kernel/trace/rv/monitors/wakeup/wakeup_trace.h
new file mode 100644
index 000000000000..7e056183f920
--- /dev/null
+++ b/kernel/trace/rv/monitors/wakeup/wakeup_trace.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Snippet to be included in rv_trace.h
+ */
+
+#ifdef CONFIG_RV_MON_WAKEUP
+DEFINE_EVENT(event_ltl_monitor_id, event_wakeup,
+	     TP_PROTO(struct task_struct *task, char *states, char *atoms, char *next),
+	     TP_ARGS(task, states, atoms, next));
+DEFINE_EVENT(error_ltl_monitor_id, error_wakeup,
+	     TP_PROTO(struct task_struct *task),
+	     TP_ARGS(task));
+#endif /* CONFIG_RV_MON_WAKEUP */
diff --git a/kernel/trace/rv/rv_trace.h b/kernel/trace/rv/rv_trace.h
index 9622c269789c..2f8a932432c9 100644
--- a/kernel/trace/rv/rv_trace.h
+++ b/kernel/trace/rv/rv_trace.h
@@ -241,6 +241,7 @@ DECLARE_EVENT_CLASS(error_ltl_monitor_id,
 );
 #include <monitors/pagefault/pagefault_trace.h>
 #include <monitors/sleep/sleep_trace.h>
+#include <monitors/wakeup/wakeup_trace.h>
 // Add new monitors based on CONFIG_LTL_MON_EVENTS_ID here
 #endif /* CONFIG_LTL_MON_EVENTS_ID */
 
diff --git a/tools/verification/models/rtapp/wakeup.ltl b/tools/verification/models/rtapp/wakeup.ltl
new file mode 100644
index 000000000000..a5d63ca0811a
--- /dev/null
+++ b/tools/verification/models/rtapp/wakeup.ltl
@@ -0,0 +1,5 @@
+RULE = always (((RT and USER_THREAD) imply
+		(not (WOKEN_BY_LOWER_PRIO or WOKEN_BY_SOFTIRQ)) or ALLOWLIST))
+
+ALLOWLIST = BLOCK_ON_RT_MUTEX
+         or FUTEX_LOCK_PI
-- 
2.47.3

Re: [PATCH 2/3] rv/rtapp/sleep: Update nanosleep rule

[Gabriele Monaco]

On Tue, 2026-05-19 at 09:49 +0200, Nam Cao wrote:
> CLOCK_REALTIME is the only clock that often is misused in real-time
> applications. The other clocks either are safe for real-time uses
> (CLOCK_TAI, CLOCK_MONOTONIC, CLOCK_BOOTTIME) or are unlikely to be misused
> (CLOCK_AUX, CLOCK_PROCESS_CPUTIME_ID).
> 
> The rtapp monitor's purpose is warning people about common mistakes with
> real-time design. However, warning about all clock types generates too much
> false positives.

I'm fine with the change, but are those really false positives?

From what I understand before this change we would report any non-rt-friendly
clock type, now only realtime.
What we are skipping would still be true positives, just so uncommon not to
justify the extra complexity, right?

Or do you mean an RT task using CLOCK_AUX is a false positive because likely the
users weren't even trying to do real-time?

Thanks,
Gabriele

> 
> Update the monitor to only warn about CLOCK_REALTIME.
> 
> Signed-off-by: Nam Cao <namcao@linutronix.de>
> ---
>  kernel/trace/rv/monitors/sleep/sleep.c    | 10 ++---
>  kernel/trace/rv/monitors/sleep/sleep.h    | 52 +++++++++++------------
>  tools/verification/models/rtapp/sleep.ltl |  2 +-
>  3 files changed, 28 insertions(+), 36 deletions(-)
> 
> diff --git a/kernel/trace/rv/monitors/sleep/sleep.c
> b/kernel/trace/rv/monitors/sleep/sleep.c
> index 0a36f5519e6b..e01ac56b3f4a 100644
> --- a/kernel/trace/rv/monitors/sleep/sleep.c
> +++ b/kernel/trace/rv/monitors/sleep/sleep.c
> @@ -43,9 +43,7 @@ static void ltl_atoms_init(struct task_struct *task, struct
> ltl_monitor *mon, bo
>  	ltl_atom_set(mon, LTL_WOKEN_BY_EQUAL_OR_HIGHER_PRIO, false);
>  
>  	if (task_creation) {
> -		ltl_atom_set(mon, LTL_KTHREAD_SHOULD_STOP, false);
> -		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_MONOTONIC, false);
> -		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_TAI, false);
> +		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_REALTIME, false);
>  		ltl_atom_set(mon, LTL_NANOSLEEP_TIMER_ABSTIME, false);
>  		ltl_atom_set(mon, LTL_CLOCK_NANOSLEEP, false);
>  		ltl_atom_set(mon, LTL_FUTEX_WAIT, false);
> @@ -136,8 +134,7 @@ static void handle_sys_enter(void *data, struct pt_regs
> *regs, long id)
>  	case __NR_clock_nanosleep_time64:
>  #endif
>  		syscall_get_arguments(current, regs, args);
> -		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_MONOTONIC, args[0] ==
> CLOCK_MONOTONIC);
> -		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_TAI, args[0] ==
> CLOCK_TAI);
> +		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_REALTIME, args[0] ==
> CLOCK_REALTIME);
>  		ltl_atom_set(mon, LTL_NANOSLEEP_TIMER_ABSTIME, args[1] ==
> TIMER_ABSTIME);
>  		ltl_atom_update(current, LTL_CLOCK_NANOSLEEP, true);
>  		break;
> @@ -178,8 +175,7 @@ static void handle_sys_exit(void *data, struct pt_regs
> *regs, long ret)
>  
>  	ltl_atom_set(mon, LTL_FUTEX_LOCK_PI, false);
>  	ltl_atom_set(mon, LTL_FUTEX_WAIT, false);
> -	ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_MONOTONIC, false);
> -	ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_TAI, false);
> +	ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_REALTIME, false);
>  	ltl_atom_set(mon, LTL_NANOSLEEP_TIMER_ABSTIME, false);
>  	ltl_atom_set(mon, LTL_EPOLL_WAIT, false);
>  	ltl_atom_update(current, LTL_CLOCK_NANOSLEEP, false);
> diff --git a/kernel/trace/rv/monitors/sleep/sleep.h
> b/kernel/trace/rv/monitors/sleep/sleep.h
> index 95dc2727c059..ed1ac7ad008e 100644
> --- a/kernel/trace/rv/monitors/sleep/sleep.h
> +++ b/kernel/trace/rv/monitors/sleep/sleep.h
> @@ -20,8 +20,7 @@ enum ltl_atom {
>  	LTL_FUTEX_WAIT,
>  	LTL_KERNEL_THREAD,
>  	LTL_KTHREAD_SHOULD_STOP,
> -	LTL_NANOSLEEP_CLOCK_MONOTONIC,
> -	LTL_NANOSLEEP_CLOCK_TAI,
> +	LTL_NANOSLEEP_CLOCK_REALTIME,
>  	LTL_NANOSLEEP_TIMER_ABSTIME,
>  	LTL_RT,
>  	LTL_SLEEP,
> @@ -46,8 +45,7 @@ static const char *ltl_atom_str(enum ltl_atom atom)
>  		"fu_wa",
>  		"ker_th",
>  		"kth_sh_st",
> -		"na_cl_mo",
> -		"na_cl_ta",
> +		"na_cl_re",
>  		"na_ti_ab",
>  		"rt",
>  		"sl",
> @@ -87,8 +85,7 @@ static void ltl_start(struct task_struct *task, struct
> ltl_monitor *mon)
>  	bool sleep = test_bit(LTL_SLEEP, mon->atoms);
>  	bool rt = test_bit(LTL_RT, mon->atoms);
>  	bool nanosleep_timer_abstime = test_bit(LTL_NANOSLEEP_TIMER_ABSTIME,
> mon->atoms);
> -	bool nanosleep_clock_tai = test_bit(LTL_NANOSLEEP_CLOCK_TAI, mon-
> >atoms);
> -	bool nanosleep_clock_monotonic =
> test_bit(LTL_NANOSLEEP_CLOCK_MONOTONIC, mon->atoms);
> +	bool nanosleep_clock_realtime =
> test_bit(LTL_NANOSLEEP_CLOCK_REALTIME, mon->atoms);
>  	bool kthread_should_stop = test_bit(LTL_KTHREAD_SHOULD_STOP, mon-
> >atoms);
>  	bool kernel_thread = test_bit(LTL_KERNEL_THREAD, mon->atoms);
>  	bool futex_wait = test_bit(LTL_FUTEX_WAIT, mon->atoms);
> @@ -97,17 +94,17 @@ static void ltl_start(struct task_struct *task, struct
> ltl_monitor *mon)
>  	bool clock_nanosleep = test_bit(LTL_CLOCK_NANOSLEEP, mon->atoms);
>  	bool block_on_rt_mutex = test_bit(LTL_BLOCK_ON_RT_MUTEX, mon->atoms);
>  	bool abort_sleep = test_bit(LTL_ABORT_SLEEP, mon->atoms);
> -	bool val42 = task_is_rcu || task_is_migration;
> -	bool val43 = futex_lock_pi || val42;
> -	bool val5 = block_on_rt_mutex || val43;
> -	bool val34 = abort_sleep || kthread_should_stop;
> -	bool val35 = woken_by_nmi || val34;
> -	bool val36 = woken_by_hardirq || val35;
> -	bool val14 = woken_by_equal_or_higher_prio || val36;
> +	bool val41 = task_is_rcu || task_is_migration;
> +	bool val42 = futex_lock_pi || val41;
> +	bool val5 = block_on_rt_mutex || val42;
> +	bool val33 = abort_sleep || kthread_should_stop;
> +	bool val34 = woken_by_nmi || val33;
> +	bool val35 = woken_by_hardirq || val34;
> +	bool val14 = woken_by_equal_or_higher_prio || val35;
>  	bool val13 = !wake;
> -	bool val26 = nanosleep_clock_monotonic || nanosleep_clock_tai;
> -	bool val27 = nanosleep_timer_abstime && val26;
> -	bool val18 = clock_nanosleep && val27;
> +	bool val25 = !nanosleep_clock_realtime;
> +	bool val26 = nanosleep_timer_abstime && val25;
> +	bool val18 = clock_nanosleep && val26;
>  	bool val20 = val18 || epoll_wait;
>  	bool val9 = futex_wait || val20;
>  	bool val11 = val9 || kernel_thread;
> @@ -138,8 +135,7 @@ ltl_possible_next_states(struct ltl_monitor *mon, unsigned
> int state, unsigned l
>  	bool sleep = test_bit(LTL_SLEEP, mon->atoms);
>  	bool rt = test_bit(LTL_RT, mon->atoms);
>  	bool nanosleep_timer_abstime = test_bit(LTL_NANOSLEEP_TIMER_ABSTIME,
> mon->atoms);
> -	bool nanosleep_clock_tai = test_bit(LTL_NANOSLEEP_CLOCK_TAI, mon-
> >atoms);
> -	bool nanosleep_clock_monotonic =
> test_bit(LTL_NANOSLEEP_CLOCK_MONOTONIC, mon->atoms);
> +	bool nanosleep_clock_realtime =
> test_bit(LTL_NANOSLEEP_CLOCK_REALTIME, mon->atoms);
>  	bool kthread_should_stop = test_bit(LTL_KTHREAD_SHOULD_STOP, mon-
> >atoms);
>  	bool kernel_thread = test_bit(LTL_KERNEL_THREAD, mon->atoms);
>  	bool futex_wait = test_bit(LTL_FUTEX_WAIT, mon->atoms);
> @@ -148,17 +144,17 @@ ltl_possible_next_states(struct ltl_monitor *mon,
> unsigned int state, unsigned l
>  	bool clock_nanosleep = test_bit(LTL_CLOCK_NANOSLEEP, mon->atoms);
>  	bool block_on_rt_mutex = test_bit(LTL_BLOCK_ON_RT_MUTEX, mon->atoms);
>  	bool abort_sleep = test_bit(LTL_ABORT_SLEEP, mon->atoms);
> -	bool val42 = task_is_rcu || task_is_migration;
> -	bool val43 = futex_lock_pi || val42;
> -	bool val5 = block_on_rt_mutex || val43;
> -	bool val34 = abort_sleep || kthread_should_stop;
> -	bool val35 = woken_by_nmi || val34;
> -	bool val36 = woken_by_hardirq || val35;
> -	bool val14 = woken_by_equal_or_higher_prio || val36;
> +	bool val41 = task_is_rcu || task_is_migration;
> +	bool val42 = futex_lock_pi || val41;
> +	bool val5 = block_on_rt_mutex || val42;
> +	bool val33 = abort_sleep || kthread_should_stop;
> +	bool val34 = woken_by_nmi || val33;
> +	bool val35 = woken_by_hardirq || val34;
> +	bool val14 = woken_by_equal_or_higher_prio || val35;
>  	bool val13 = !wake;
> -	bool val26 = nanosleep_clock_monotonic || nanosleep_clock_tai;
> -	bool val27 = nanosleep_timer_abstime && val26;
> -	bool val18 = clock_nanosleep && val27;
> +	bool val25 = !nanosleep_clock_realtime;
> +	bool val26 = nanosleep_timer_abstime && val25;
> +	bool val18 = clock_nanosleep && val26;
>  	bool val20 = val18 || epoll_wait;
>  	bool val9 = futex_wait || val20;
>  	bool val11 = val9 || kernel_thread;
> diff --git a/tools/verification/models/rtapp/sleep.ltl
> b/tools/verification/models/rtapp/sleep.ltl
> index 6f26c4810f78..2637bc48a620 100644
> --- a/tools/verification/models/rtapp/sleep.ltl
> +++ b/tools/verification/models/rtapp/sleep.ltl
> @@ -9,7 +9,7 @@ RT_VALID_SLEEP_REASON = FUTEX_WAIT
>  
>  RT_FRIENDLY_NANOSLEEP = CLOCK_NANOSLEEP
>                      and NANOSLEEP_TIMER_ABSTIME
> -                    and (NANOSLEEP_CLOCK_MONOTONIC or NANOSLEEP_CLOCK_TAI)
> +                    and not NANOSLEEP_CLOCK_REALTIME
>  
>  RT_FRIENDLY_WAKE = WOKEN_BY_EQUAL_OR_HIGHER_PRIO
>                  or WOKEN_BY_HARDIRQ

Re: [PATCH 2/3] rv/rtapp/sleep: Update nanosleep rule

[Nam Cao]

Gabriele Monaco <gmonaco@redhat.com> writes:

> On Tue, 2026-05-19 at 09:49 +0200, Nam Cao wrote:
>> CLOCK_REALTIME is the only clock that often is misused in real-time
>> applications. The other clocks either are safe for real-time uses
>> (CLOCK_TAI, CLOCK_MONOTONIC, CLOCK_BOOTTIME) or are unlikely to be misused
>> (CLOCK_AUX, CLOCK_PROCESS_CPUTIME_ID).
>> 
>> The rtapp monitor's purpose is warning people about common mistakes with
>> real-time design. However, warning about all clock types generates too much
>> false positives.
>
> I'm fine with the change, but are those really false positives?
>
> From what I understand before this change we would report any non-rt-friendly
> clock type, now only realtime.
> What we are skipping would still be true positives, just so uncommon not to
> justify the extra complexity, right?
>
> Or do you mean an RT task using CLOCK_AUX is a false positive because likely the
> users weren't even trying to do real-time?

CLOCK_BOOTTIME is fine for RT.

CLOCK_AUX is created for real-time use cases, so the monitor shouldn't
warn about it. But this clock can also be arbitrarily set, which can be
unsafe (e.g. you want to deploy the air bag in 10us, but someone changes
the clock and you have to wait 10s).

We probably can detect if a clock used by an RT task is set, but I am
not sure how complicated that is, if even possible. For now we are
assuming that user won't do such thing, then CLOCK_AUX is fine for RT
uses.

CLOCK_PROCESS_CPUTIME_ID is a strange one and shouldn't be used for
real-time. But I think it's obvious from the description that you cannot
do real-time with that.

Only CLOCK_REALTIME is a mistake people often make, probably has
something to do with the deceptive name.

Nam

Re: [PATCH 1/3] rv/rtapp/sleep: Make the error more informative for user

[Gabriele Monaco]

On Tue, 2026-05-19 at 09:49 +0200, Nam Cao wrote:
> The rtapp/sleep monitor detects real-time tasks which go to sleep in an
> real-time-unsafe manner. If this happen, the monitor triggers a trace event
> in the sched_wakeup tracepoint's handler.
> 

Ok so here WAKE is no longer tied to the wakeup event but to the end of the task
switch.

So what happens if a task was not sleeping but just got preempted? Wouldn't that
trigger WAKE (though that isn't a real wakeup) without RT_FRIENDLY_WAKE ?

Thanks,
Gabriele

> However, the invoking context of that trace event is not the most
> informative, because of the stack trace of that event is the wakeup's code
> path which is not very helpful:
> 
> 74.669317: rv:error_sleep: condvar[254]: violation detected
>     ltl_validate+0x345 ([kernel.kallsyms])
>     handle_sched_wakeup+0x34 ([kernel.kallsyms])
>     ttwu_do_activate+0xff ([kernel.kallsyms])
>     sched_ttwu_pending+0x104 ([kernel.kallsyms])
>     __flush_smp_call_function_queue+0x15b ([kernel.kallsyms])
>     __sysvec_call_function_single+0x18 ([kernel.kallsyms])
>     sysvec_call_function_single+0x66 ([kernel.kallsyms])
>     asm_sysvec_call_function_single+0x1a ([kernel.kallsyms])
>     pv_native_safe_halt+0xf ([kernel.kallsyms])
>     default_idle+0x9 ([kernel.kallsyms])
>     default_idle_call+0x33 ([kernel.kallsyms])
>     do_idle+0x234 ([kernel.kallsyms])
>     cpu_startup_entry+0x24 ([kernel.kallsyms])
>     start_secondary+0xf8 ([kernel.kallsyms])
>     common_startup_64+0x13e ([kernel.kallsyms])
> 
> What would be much more valuable is the stack trace of the task itself.
> 
> Change the update of WAKEUP from being in sched_wakeup trace point's
> handler to sched_exit trace point's handler. This makes the event happen in
> the task's context, making the stack trace far more informative for user:
> 
> rv:error_sleep: condvar[254]: violation detected
>     ltl_validate+0x345 ([kernel.kallsyms])
>     handle_sched_exit+0x39 ([kernel.kallsyms])
>     __schedule+0x80f ([kernel.kallsyms])
>     schedule+0x22 ([kernel.kallsyms])
>     futex_do_wait+0x33 ([kernel.kallsyms])
>     __futex_wait+0x8c ([kernel.kallsyms])
>     futex_wait+0x73 ([kernel.kallsyms])
>     do_futex+0xc6 ([kernel.kallsyms])
>     __x64_sys_futex+0x121 ([kernel.kallsyms])
>     do_syscall_64+0xf3 ([kernel.kallsyms])
>     entry_SYSCALL_64_after_hwframe+0x77 ([kernel.kallsyms])
>     __futex_abstimed_wait_common64+0xc6 (inlined)
>     __futex_abstimed_wait_common+0xc6 (/usr/lib/x86_64-linux-gnu/libc.so.6)
> 
> Signed-off-by: Nam Cao <namcao@linutronix.de>
> ---
>  kernel/trace/rv/monitors/sleep/sleep.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/rv/monitors/sleep/sleep.c
> b/kernel/trace/rv/monitors/sleep/sleep.c
> index 8dfe5ec13e19..0a36f5519e6b 100644
> --- a/kernel/trace/rv/monitors/sleep/sleep.c
> +++ b/kernel/trace/rv/monitors/sleep/sleep.c
> @@ -92,9 +92,9 @@ static void handle_sched_set_state(void *data, struct
> task_struct *task, int sta
>  		ltl_atom_pulse(task, LTL_ABORT_SLEEP, true);
>  }
>  
> -static void handle_sched_wakeup(void *data, struct task_struct *task)
> +static void handle_sched_exit(void *data, bool is_switch)
>  {
> -	ltl_atom_pulse(task, LTL_WAKE, true);
> +	ltl_atom_pulse(current, LTL_WAKE, true);
>  }
>  
>  static void handle_sched_waking(void *data, struct task_struct *task)
> @@ -200,7 +200,7 @@ static int enable_sleep(void)
>  		return retval;
>  
>  	rv_attach_trace_probe("rtapp_sleep", sched_waking,
> handle_sched_waking);
> -	rv_attach_trace_probe("rtapp_sleep", sched_wakeup,
> handle_sched_wakeup);
> +	rv_attach_trace_probe("rtapp_sleep", sched_exit_tp,
> handle_sched_exit);
>  	rv_attach_trace_probe("rtapp_sleep", sched_set_state_tp,
> handle_sched_set_state);
>  	rv_attach_trace_probe("rtapp_sleep", contention_begin,
> handle_contention_begin);
>  	rv_attach_trace_probe("rtapp_sleep", contention_end,
> handle_contention_end);
> @@ -213,7 +213,7 @@ static int enable_sleep(void)
>  static void disable_sleep(void)
>  {
>  	rv_detach_trace_probe("rtapp_sleep", sched_waking,
> handle_sched_waking);
> -	rv_detach_trace_probe("rtapp_sleep", sched_wakeup,
> handle_sched_wakeup);
> +	rv_detach_trace_probe("rtapp_sleep", sched_exit_tp,
> handle_sched_exit);
>  	rv_detach_trace_probe("rtapp_sleep", sched_set_state_tp,
> handle_sched_set_state);
>  	rv_detach_trace_probe("rtapp_sleep", contention_begin,
> handle_contention_begin);
>  	rv_detach_trace_probe("rtapp_sleep", contention_end,
> handle_contention_end);

Re: [PATCH 1/3] rv/rtapp/sleep: Make the error more informative for user

[Nam Cao]

Gabriele Monaco <gmonaco@redhat.com> writes:
> On Tue, 2026-05-19 at 09:49 +0200, Nam Cao wrote:
>> The rtapp/sleep monitor detects real-time tasks which go to sleep in an
>> real-time-unsafe manner. If this happen, the monitor triggers a trace event
>> in the sched_wakeup tracepoint's handler.
>
> Ok so here WAKE is no longer tied to the wakeup event but to the end of the task
> switch.
>
> So what happens if a task was not sleeping but just got preempted? Wouldn't that
> trigger WAKE (though that isn't a real wakeup) without RT_FRIENDLY_WAKE ?

The monitor's rule says that when a task sleeps, it will not wake
without rt-friendly wake. If it "wakes" without initial sleep, it is
simply ignored.

I can change the name to be SCHEDULE_IN or something like that to make
it clearer.

Nam

Re: [PATCH 1/3] rv/rtapp/sleep: Make the error more informative for user

[Gabriele Monaco]

On Tue, 2026-05-19 at 17:24 +0200, Nam Cao wrote:
> Gabriele Monaco <gmonaco@redhat.com> writes:
> > On Tue, 2026-05-19 at 09:49 +0200, Nam Cao wrote:
> > > The rtapp/sleep monitor detects real-time tasks which go to sleep in an
> > > real-time-unsafe manner. If this happen, the monitor triggers a trace
> > > event
> > > in the sched_wakeup tracepoint's handler.
> > 
> > Ok so here WAKE is no longer tied to the wakeup event but to the end of the
> > task
> > switch.
> > 
> > So what happens if a task was not sleeping but just got preempted? Wouldn't
> > that
> > trigger WAKE (though that isn't a real wakeup) without RT_FRIENDLY_WAKE ?
> 
> The monitor's rule says that when a task sleeps, it will not wake
> without rt-friendly wake. If it "wakes" without initial sleep, it is
> simply ignored.

Right makes sense.

> I can change the name to be SCHEDULE_IN or something like that to make
> it clearer.
> 

Yeah that'd be clearer, or at least a comment stating this somewhere.

Thanks,
Gabriele