[RFC PATCH lttng-modules] Fix: update sched prev_state instrumentation for kernel 4.14.0 and 4.20.0

[Gabriel-Andrew Pollo-Guilbert <gabriel.pollo-guilbert@efficios.com>]

Upstream Linux kernel commit in 4.14.0:

commit efb40f588b4370ffaeffafbd50f6ff213d954254
Author: Peter Zijlstra <peterz@infradead.org>
Date:   Fri Sep 22 18:19:53 2017 +0200

    sched/tracing: Fix trace_sched_switch task-state printing

commit 3f5fe9fef5b2da06b6319fab8123056da5217c3f
Author: Thomas Gleixner <tglx@linutronix.de>
Date:   Wed Nov 22 13:05:48 2017 +0100

    sched/debug: Fix task state recording/printout

Upstream Linux kernel commit in 4.20.0:

commit 3054426dc68e5d63aa6a6e9b91ac4ec78e3f3805
Author: Pavankumar Kondeti <pkondeti@codeaurora.org>
Date:   Tue Oct 30 12:24:33 2018 +0530

    sched, trace: Fix prev_state output in sched_switch tracepoint

Signed-off-by: Gabriel-Andrew Pollo-Guilbert <gabriel.pollo-guilbert@efficios.com>
---
 instrumentation/events/lttng-module/sched.h | 47 ++++++++++++++++++++-
 1 file changed, 46 insertions(+), 1 deletion(-)

diff --git a/instrumentation/events/lttng-module/sched.h b/instrumentation/events/lttng-module/sched.h
index 77d77b2..f27cee5 100644
--- a/instrumentation/events/lttng-module/sched.h
+++ b/instrumentation/events/lttng-module/sched.h
@@ -25,7 +25,52 @@
 #ifndef _TRACE_SCHED_DEF_
 #define _TRACE_SCHED_DEF_
 
-#if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,4,0))
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,20,0))
+
+static inline long __trace_sched_switch_state(bool preempt, struct task_struct *p)
+{
+        unsigned int state;
+
+#ifdef CONFIG_SCHED_DEBUG
+        BUG_ON(p != current);
+#endif /* CONFIG_SCHED_DEBUG */
+
+        /*
+         * Preemption ignores task state, therefore preempted tasks are always
+         * RUNNING (we will not have dequeued if state != RUNNING).
+         */
+        if (preempt)
+                return TASK_REPORT_MAX;
+
+        /*
+         * task_state_index() uses fls() and returns a value from 0-8 range.
+         * Decrement it by 1 (except TASK_RUNNING state i.e 0) before using
+         * it for left shift operation to get the correct task->state
+         * mapping.
+         */
+        state = task_state_index(p);
+
+        return state ? (1 << (state - 1)) : state;
+}
+
+#elif (LINUX_VERSION_CODE >= KERNEL_VERSION(4,14,0))
+
+static inline long __trace_sched_switch_state(bool preempt, struct task_struct *p)
+{
+#ifdef CONFIG_SCHED_DEBUG
+	BUG_ON(p != current);
+#endif /* CONFIG_SCHED_DEBUG */
+	/*
+	 * Preemption ignores task state, therefore preempted tasks are always RUNNING
+	 * (we will not have dequeued if state != RUNNING).
+	 */
+        if (preempt)
+                return TASK_REPORT_MAX;
+
+        return 1 << task_state_index(p);
+}
+
+#elif (LINUX_VERSION_CODE >= KERNEL_VERSION(4,4,0))
 
 static inline long __trace_sched_switch_state(bool preempt, struct task_struct *p)
 {
-- 
2.22.0