Add "real-time scheduling" monitor, which validates that SCHED_RR and
SCHED_FIFO tasks are scheduled before tasks with normal and extensible
scheduling policies

Reviewed-by: Gabriele Monaco <gmon...@redhat.com>
Signed-off-by: Nam Cao <nam...@linutronix.de>
---
Cc: Ingo Molnar <mi...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Juri Lelli <juri.le...@redhat.com>
Cc: Vincent Guittot <vincent.guit...@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggem...@arm.com>
Cc: Ben Segall <bseg...@google.com>
Cc: Mel Gorman <mgor...@suse.de>
Cc: Valentin Schneider <vschn...@redhat.com>
Cc: K Prateek Nayak <kprateek.na...@amd.com>
---
v3:
  - move document file and specification file to be under rtapp
v2:
  - use the new tracepoints
  - move to be under the rtapp container monitor
  - re-generate with the modified scripts
  - fixup incorrect enqueued status
---
 Documentation/trace/rv/monitor_rtapp.rst |  19 +++
 kernel/trace/rv/Kconfig                  |   1 +
 kernel/trace/rv/Makefile                 |   1 +
 kernel/trace/rv/monitors/rts/Kconfig     |  17 +++
 kernel/trace/rv/monitors/rts/rts.c       | 144 +++++++++++++++++++++++
 kernel/trace/rv/monitors/rts/rts.h       | 126 ++++++++++++++++++++
 kernel/trace/rv/monitors/rts/rts_trace.h |  15 +++
 kernel/trace/rv/rv_trace.h               |   1 +
 tools/verification/models/rtapp/rts.ltl  |   5 +
 9 files changed, 329 insertions(+)
 create mode 100644 kernel/trace/rv/monitors/rts/Kconfig
 create mode 100644 kernel/trace/rv/monitors/rts/rts.c
 create mode 100644 kernel/trace/rv/monitors/rts/rts.h
 create mode 100644 kernel/trace/rv/monitors/rts/rts_trace.h
 create mode 100644 tools/verification/models/rtapp/rts.ltl

diff --git a/Documentation/trace/rv/monitor_rtapp.rst 
b/Documentation/trace/rv/monitor_rtapp.rst
index c8104eda924a..40001ace5612 100644
--- a/Documentation/trace/rv/monitor_rtapp.rst
+++ b/Documentation/trace/rv/monitor_rtapp.rst
@@ -131,3 +131,22 @@ special cases:
     real-time-safe because preemption is disabled for the duration.
   - `FUTEX_LOCK_PI` is included in the allowlist for the same reason as
     `BLOCK_ON_RT_MUTEX`.
+
+Monitor rts
++++++++++++
+
+The real-time scheduling monitor validates that tasks with real-time scheduling
+policies (`SCHED_FIFO` and `SCHED_RR`) are always scheduled before tasks with
+normal and extensible scheduling policies (`SCHED_OTHER`, `SCHED_BATCH`,
+`SCHED_IDLE`, `SCHED_EXT`):
+
+.. literalinclude:: ../../../tools/verification/models/rtapp/rts.ltl
+
+Note that this monitor may report errors if real-time throttling or fair
+deadline server is enabled. These mechanisms prevent real-time tasks from
+monopolying the CPU by giving tasks with normal and extensible scheduling
+policies a chance to run. They give system administrators a chance to kill a
+misbehaved real-time task. However, they violate the scheduling priorities and
+may cause latency to well-behaved real-time tasks. Thus, if you see errors from
+this monitor, consider disabling real-time throttling and the fair deadline
+server.
diff --git a/kernel/trace/rv/Kconfig b/kernel/trace/rv/Kconfig
index 7ef89006ed50..e9007ed32aea 100644
--- a/kernel/trace/rv/Kconfig
+++ b/kernel/trace/rv/Kconfig
@@ -67,6 +67,7 @@ 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/rts/Kconfig"
 # Add new rtapp monitors here
 
 # Add new monitors here
diff --git a/kernel/trace/rv/Makefile b/kernel/trace/rv/Makefile
index 750e4ad6fa0f..d7bfc7ae6677 100644
--- a/kernel/trace/rv/Makefile
+++ b/kernel/trace/rv/Makefile
@@ -17,6 +17,7 @@ obj-$(CONFIG_RV_MON_STS) += monitors/sts/sts.o
 obj-$(CONFIG_RV_MON_NRP) += monitors/nrp/nrp.o
 obj-$(CONFIG_RV_MON_SSSW) += monitors/sssw/sssw.o
 obj-$(CONFIG_RV_MON_OPID) += monitors/opid/opid.o
+obj-$(CONFIG_RV_MON_RTS) += monitors/rts/rts.o
 # Add new monitors here
 obj-$(CONFIG_RV_REACTORS) += rv_reactors.o
 obj-$(CONFIG_RV_REACT_PRINTK) += reactor_printk.o
diff --git a/kernel/trace/rv/monitors/rts/Kconfig 
b/kernel/trace/rv/monitors/rts/Kconfig
new file mode 100644
index 000000000000..5481b371bce1
--- /dev/null
+++ b/kernel/trace/rv/monitors/rts/Kconfig
@@ -0,0 +1,17 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+config RV_MON_RTS
+       depends on RV
+       select RV_LTL_MONITOR
+       depends on RV_MON_RTAPP
+       default y
+       select LTL_MON_EVENTS_CPU
+       bool "rts monitor"
+       help
+         Add support for RTS (real-time scheduling) monitor which validates
+         that real-time-priority tasks are scheduled before SCHED_OTHER tasks.
+
+         This monitor may report an error if RT throttling or deadline server
+         is enabled.
+
+         Say Y if you are debugging or testing a real-time system.
diff --git a/kernel/trace/rv/monitors/rts/rts.c 
b/kernel/trace/rv/monitors/rts/rts.c
new file mode 100644
index 000000000000..b4c3d3a4671d
--- /dev/null
+++ b/kernel/trace/rv/monitors/rts/rts.c
@@ -0,0 +1,144 @@
+// 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 <linux/sched/deadline.h>
+#include <linux/sched/rt.h>
+#include <rv/instrumentation.h>
+
+#define MODULE_NAME "rts"
+
+#include <trace/events/sched.h>
+#include <rv_trace.h>
+#include <monitors/rtapp/rtapp.h>
+
+#include "rts.h"
+#include <rv/ltl_monitor.h>
+
+static DEFINE_PER_CPU(unsigned int, nr_queued);
+
+static void ltl_atoms_fetch(unsigned int cpu, struct ltl_monitor *mon)
+{
+}
+
+static void ltl_atoms_init(unsigned int cpu, struct ltl_monitor *mon,
+                          bool target_creation)
+{
+       ltl_atom_set(mon, LTL_SCHED_SWITCH, false);
+       ltl_atom_set(mon, LTL_SCHED_SWITCH_DL, false);
+       ltl_atom_set(mon, LTL_SCHED_SWITCH_RT, false);
+
+       /*
+        * This may not be accurate, there may be enqueued RT tasks. But that's
+        * okay, the worst we get is a false negative. It will be accurate as
+        * soon as the CPU no longer has any queued RT task.
+        */
+       ltl_atom_set(mon, LTL_RT_TASK_ENQUEUED, false);
+}
+
+static void handle_enqueue_task(void *data, int cpu, struct task_struct *task)
+{
+       unsigned int *queued = per_cpu_ptr(&nr_queued, cpu);
+
+       if (!rt_task(task))
+               return;
+
+       (*queued)++;
+       ltl_atom_update(cpu, LTL_RT_TASK_ENQUEUED, true);
+}
+
+static void handle_dequeue_task(void *data, int cpu, struct task_struct *task)
+{
+       unsigned int *queued = per_cpu_ptr(&nr_queued, cpu);
+
+       if (!rt_task(task))
+               return;
+
+       /*
+        * This may not be accurate for a short time after the monitor is
+        * enabled, because there may be enqueued RT tasks which are not counted
+        * torward nr_queued. But that's okay, the worst we get is a false
+        * negative. nr_queued will be accurate as soon as the CPU no longer has
+        * any queued RT task.
+        */
+       if (*queued)
+               (*queued)--;
+       if (!*queued)
+               ltl_atom_update(cpu, LTL_RT_TASK_ENQUEUED, false);
+}
+
+static void handle_sched_switch(void *data, bool preempt, struct task_struct 
*prev,
+                               struct task_struct *next, unsigned int 
prev_state)
+{
+       unsigned int cpu = smp_processor_id();
+       struct ltl_monitor *mon = ltl_get_monitor(cpu);
+
+       ltl_atom_set(mon, LTL_SCHED_SWITCH_RT, rt_task(next));
+       ltl_atom_set(mon, LTL_SCHED_SWITCH_DL, dl_task(next));
+       ltl_atom_update(cpu, LTL_SCHED_SWITCH, true);
+
+       ltl_atom_set(mon, LTL_SCHED_SWITCH_RT, false);
+       ltl_atom_set(mon, LTL_SCHED_SWITCH_DL, false);
+       ltl_atom_update(cpu, LTL_SCHED_SWITCH, false);
+}
+
+static int enable_rts(void)
+{
+       unsigned int cpu;
+       int retval;
+
+       retval = ltl_monitor_init();
+       if (retval)
+               return retval;
+
+       for_each_possible_cpu(cpu) {
+               unsigned int *queued = per_cpu_ptr(&nr_queued, cpu);
+
+               *queued = 0;
+       }
+
+       rv_attach_trace_probe("rts", dequeue_task_tp, handle_dequeue_task);
+       rv_attach_trace_probe("rts", enqueue_task_tp, handle_enqueue_task);
+       rv_attach_trace_probe("rts", sched_switch, handle_sched_switch);
+
+       return 0;
+}
+
+static void disable_rts(void)
+{
+       rv_detach_trace_probe("rts", sched_switch, handle_sched_switch);
+       rv_detach_trace_probe("rts", enqueue_task_tp, handle_enqueue_task);
+       rv_detach_trace_probe("rts", dequeue_task_tp, handle_dequeue_task);
+
+       ltl_monitor_destroy();
+}
+
+/*
+ * This is the monitor register section.
+ */
+static struct rv_monitor rv_rts = {
+       .name = "rts",
+       .description = "Validate that real-time tasks are scheduled before 
lower-priority tasks",
+       .enable = enable_rts,
+       .disable = disable_rts,
+};
+
+static int __init register_rts(void)
+{
+       return rv_register_monitor(&rv_rts, &rv_rtapp);
+}
+
+static void __exit unregister_rts(void)
+{
+       rv_unregister_monitor(&rv_rts);
+}
+
+module_init(register_rts);
+module_exit(unregister_rts);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Nam Cao <nam...@linutronix.de>");
+MODULE_DESCRIPTION("rts: Validate that real-time tasks are scheduled before 
lower-priority tasks");
diff --git a/kernel/trace/rv/monitors/rts/rts.h 
b/kernel/trace/rv/monitors/rts/rts.h
new file mode 100644
index 000000000000..5881f30a38ce
--- /dev/null
+++ b/kernel/trace/rv/monitors/rts/rts.h
@@ -0,0 +1,126 @@
+/* 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 rts
+
+#define LTL_MONITOR_TYPE RV_MON_PER_CPU
+
+enum ltl_atom {
+       LTL_RT_TASK_ENQUEUED,
+       LTL_SCHED_SWITCH,
+       LTL_SCHED_SWITCH_DL,
+       LTL_SCHED_SWITCH_RT,
+       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[] = {
+               "rt_ta_en",
+               "sc_sw",
+               "sc_sw_dl",
+               "sc_sw_rt",
+       };
+
+       return names[atom];
+}
+
+enum ltl_buchi_state {
+       S0,
+       S1,
+       S2,
+       S3,
+       S4,
+       RV_NUM_BA_STATES
+};
+static_assert(RV_NUM_BA_STATES <= RV_MAX_BA_STATES);
+
+static void ltl_start(unsigned int cpu, struct ltl_monitor *mon)
+{
+       bool sched_switch_rt = test_bit(LTL_SCHED_SWITCH_RT, mon->atoms);
+       bool sched_switch_dl = test_bit(LTL_SCHED_SWITCH_DL, mon->atoms);
+       bool sched_switch = test_bit(LTL_SCHED_SWITCH, mon->atoms);
+       bool rt_task_enqueued = test_bit(LTL_RT_TASK_ENQUEUED, mon->atoms);
+       bool val13 = !rt_task_enqueued;
+       bool val8 = sched_switch_dl || val13;
+       bool val9 = sched_switch_rt || val8;
+       bool val6 = !sched_switch;
+       bool val1 = !rt_task_enqueued;
+
+       if (val1)
+               __set_bit(S0, mon->states);
+       if (val6)
+               __set_bit(S1, mon->states);
+       if (val9)
+               __set_bit(S4, mon->states);
+}
+
+static void
+ltl_possible_next_states(struct ltl_monitor *mon, unsigned int state, unsigned 
long *next)
+{
+       bool sched_switch_rt = test_bit(LTL_SCHED_SWITCH_RT, mon->atoms);
+       bool sched_switch_dl = test_bit(LTL_SCHED_SWITCH_DL, mon->atoms);
+       bool sched_switch = test_bit(LTL_SCHED_SWITCH, mon->atoms);
+       bool rt_task_enqueued = test_bit(LTL_RT_TASK_ENQUEUED, mon->atoms);
+       bool val13 = !rt_task_enqueued;
+       bool val8 = sched_switch_dl || val13;
+       bool val9 = sched_switch_rt || val8;
+       bool val6 = !sched_switch;
+       bool val1 = !rt_task_enqueued;
+
+       switch (state) {
+       case S0:
+               if (val1)
+                       __set_bit(S0, next);
+               if (val6)
+                       __set_bit(S1, next);
+               if (val9)
+                       __set_bit(S4, next);
+               break;
+       case S1:
+               if (val6)
+                       __set_bit(S1, next);
+               if (val1 && val6)
+                       __set_bit(S2, next);
+               if (val1 && val9)
+                       __set_bit(S3, next);
+               if (val9)
+                       __set_bit(S4, next);
+               break;
+       case S2:
+               if (val6)
+                       __set_bit(S1, next);
+               if (val1 && val6)
+                       __set_bit(S2, next);
+               if (val1 && val9)
+                       __set_bit(S3, next);
+               if (val9)
+                       __set_bit(S4, next);
+               break;
+       case S3:
+               if (val1)
+                       __set_bit(S0, next);
+               if (val6)
+                       __set_bit(S1, next);
+               if (val9)
+                       __set_bit(S4, next);
+               break;
+       case S4:
+               if (val1)
+                       __set_bit(S0, next);
+               if (val6)
+                       __set_bit(S1, next);
+               if (val9)
+                       __set_bit(S4, next);
+               break;
+       }
+}
diff --git a/kernel/trace/rv/monitors/rts/rts_trace.h 
b/kernel/trace/rv/monitors/rts/rts_trace.h
new file mode 100644
index 000000000000..ac4ea84162f7
--- /dev/null
+++ b/kernel/trace/rv/monitors/rts/rts_trace.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Snippet to be included in rv_trace.h
+ */
+
+#ifdef CONFIG_RV_MON_RTS
+DEFINE_EVENT(event_ltl_monitor_cpu, event_rts,
+       TP_PROTO(unsigned int cpu, char *states, char *atoms, char *next),
+       TP_ARGS(cpu, states, atoms, next));
+
+DEFINE_EVENT(error_ltl_monitor_cpu, error_rts,
+       TP_PROTO(unsigned int cpu),
+       TP_ARGS(cpu));
+#endif /* CONFIG_RV_MON_RTS */
diff --git a/kernel/trace/rv/rv_trace.h b/kernel/trace/rv/rv_trace.h
index bf7cca6579ec..7b3a6fb8ca6f 100644
--- a/kernel/trace/rv/rv_trace.h
+++ b/kernel/trace/rv/rv_trace.h
@@ -221,6 +221,7 @@ DECLARE_EVENT_CLASS(error_ltl_monitor_cpu,
 
        TP_printk("cpu%u: violation detected", __entry->cpu)
 );
+#include <monitors/rts/rts_trace.h>
 // Add new monitors based on CONFIG_LTL_MON_EVENTS_CPU here
 
 #endif /* CONFIG_LTL_MON_EVENTS_CPU */
diff --git a/tools/verification/models/rtapp/rts.ltl 
b/tools/verification/models/rtapp/rts.ltl
new file mode 100644
index 000000000000..90872bca46b1
--- /dev/null
+++ b/tools/verification/models/rtapp/rts.ltl
@@ -0,0 +1,5 @@
+RULE = always (RT_TASK_ENQUEUED imply SCHEDULE_RT_NEXT)
+
+SCHEDULE_RT_NEXT = (not SCHED_SWITCH) until (SCHED_SWITCH_RT or EXCEPTIONS)
+
+EXCEPTIONS = SCHED_SWITCH_DL or not RT_TASK_ENQUEUED
-- 
2.39.5


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