rv: Replace tss and sncid monitors with more complete sts

The tss monitor currently guarantees task switches can happen only while
scheduling, whereas the sncid monitor enforces scheduling occurs with
interrupt disabled.

Replace the monitors with a more comprehensive specification which
implies both but also ensures that:
* each scheduler call disable interrupts to switch
* each task switch happens with interrupts disabled

Cc: Ingo Molnar <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Nam Cao <[email protected]>
Cc: Tomas Glozar <[email protected]>
Cc: Juri Lelli <[email protected]>
Cc: Clark Williams <[email protected]>
Cc: John Kacur <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Gabriele Monaco <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

Author: glemco

Documentation/trace/rv/monitor_sched.rst

@@ -40,26 +40,6 @@ defined in by Daniel Bristot in [1].
 
 Currently we included the following:
 
-Monitor tss
-~~~~~~~~~~~
-
-The task switch while scheduling (tss) monitor ensures a task switch happens
-only in scheduling context, that is inside a call to `__schedule`::
-
-                     |
-                     |
-                     v
-                   +-----------------+
-                   |     thread      | <+
-                   +-----------------+  |
-                     |                  |
-                     | schedule_entry   | schedule_exit
-                     v                  |
-    sched_switch                        |
-  +---------------                      |
-  |                       sched         |
-  +-------------->                     -+
-
 Monitor sco
 ~~~~~~~~~~~
 
@@ -144,26 +124,55 @@ does not enable preemption::
                                                   |
                           scheduling_contex      -+
 
-Monitor sncid
-~~~~~~~~~~~~~
-
-The schedule not called with interrupt disabled (sncid) monitor ensures
-schedule is not called with interrupt disabled::
+Monitor sts
+~~~~~~~~~~~
 
-                       |
-                       |
-                       v
-    schedule_entry   +--------------+
-    schedule_exit    |              |
-  +----------------- |  can_sched   |
-  |                  |              |
-  +----------------> |              | <+
-                     +--------------+  |
-                       |               |
-                       | irq_disable   | irq_enable
-                       v               |
-                                       |
-                        cant_sched    -+
+The schedule implies task switch (sts) monitor ensures a task switch happens
+only in scheduling context and up to once, as well as scheduling occurs with
+interrupts enabled but no task switch can happen before interrupts are
+disabled. When the next task picked for execution is the same as the previously
+running one, no real task switch occurs but interrupts are disabled nonetheless::
+
+    irq_entry                      |
+     +----+                        |
+     v    |                        v
+ +------------+ irq_enable    #===================#   irq_disable
+ |            | ------------> H                   H   irq_entry
+ | cant_sched | <------------ H                   H   irq_enable
+ |            | irq_disable   H     can_sched     H --------------+
+ +------------+               H                   H               |
+                              H                   H               |
+            +---------------> H                   H <-------------+
+            |                 #===================#
+            |                   |
+      schedule_exit             | schedule_entry
+            |                   v
+            |   +-------------------+     irq_enable
+            |   |    scheduling     | <---------------+
+            |   +-------------------+                 |
+            |     |                                   |
+            |     | irq_disable                    +--------+  irq_entry
+            |     v                                |        | --------+
+            |   +-------------------+  irq_entry   | in_irq |         |
+            |   |                   | -----------> |        | <-------+
+            |   | disable_to_switch |              +--------+
+            |   |                   | --+
+            |   +-------------------+   |
+            |     |                     |
+            |     | sched_switch        |
+            |     v                     |
+            |   +-------------------+   |
+            |   |     switching     |   | irq_enable
+            |   +-------------------+   |
+            |     |                     |
+            |     | irq_enable          |
+            |     v                     |
+            |   +-------------------+   |
+            +-- |  enable_to_exit   | <-+
+                +-------------------+
+                  ^               | irq_disable
+                  |               | irq_entry
+                  +---------------+ irq_enable
 
 References
 ----------

kernel/trace/rv/Kconfig

@@ -50,12 +50,11 @@ source "kernel/trace/rv/monitors/wip/Kconfig"
 source "kernel/trace/rv/monitors/wwnr/Kconfig"
 
 source "kernel/trace/rv/monitors/sched/Kconfig"
-source "kernel/trace/rv/monitors/tss/Kconfig"
 source "kernel/trace/rv/monitors/sco/Kconfig"
 source "kernel/trace/rv/monitors/snroc/Kconfig"
 source "kernel/trace/rv/monitors/scpd/Kconfig"
 source "kernel/trace/rv/monitors/snep/Kconfig"
-source "kernel/trace/rv/monitors/sncid/Kconfig"
+source "kernel/trace/rv/monitors/sts/Kconfig"
 # Add new sched monitors here
 
 source "kernel/trace/rv/monitors/rtapp/Kconfig"

kernel/trace/rv/Makefile

@@ -6,15 +6,14 @@ obj-$(CONFIG_RV) += rv.o
 obj-$(CONFIG_RV_MON_WIP) += monitors/wip/wip.o
 obj-$(CONFIG_RV_MON_WWNR) += monitors/wwnr/wwnr.o
 obj-$(CONFIG_RV_MON_SCHED) += monitors/sched/sched.o
-obj-$(CONFIG_RV_MON_TSS) += monitors/tss/tss.o
 obj-$(CONFIG_RV_MON_SCO) += monitors/sco/sco.o
 obj-$(CONFIG_RV_MON_SNROC) += monitors/snroc/snroc.o
 obj-$(CONFIG_RV_MON_SCPD) += monitors/scpd/scpd.o
 obj-$(CONFIG_RV_MON_SNEP) += monitors/snep/snep.o
-obj-$(CONFIG_RV_MON_SNCID) += monitors/sncid/sncid.o
 obj-$(CONFIG_RV_MON_RTAPP) += monitors/rtapp/rtapp.o
 obj-$(CONFIG_RV_MON_PAGEFAULT) += monitors/pagefault/pagefault.o
 obj-$(CONFIG_RV_MON_SLEEP) += monitors/sleep/sleep.o
+obj-$(CONFIG_RV_MON_STS) += monitors/sts/sts.o
 # Add new monitors here
 obj-$(CONFIG_RV_REACTORS) += rv_reactors.o
 obj-$(CONFIG_RV_REACT_PRINTK) += reactor_printk.o

kernel/trace/rv/monitors/sncid/Kconfig

@@ -0,0 +1,19 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+config RV_MON_STS
+	depends on RV
+	depends on TRACE_IRQFLAGS
+	depends on RV_MON_SCHED
+	default y
+	select DA_MON_EVENTS_IMPLICIT
+	bool "sts monitor"
+	help
+	  Monitor to ensure relationships between scheduler and task switches
+	   * the scheduler is called and returns with interrupts disabled
+	   * each call to the scheduler has up to one switch
+	   * switches only happen inside the scheduler
+	   * each call to the scheduler disables interrupts to switch
+	  This monitor is part of the sched monitors collection.
+
+	  For further information, see:
+	    Documentation/trace/rv/monitor_sched.rst