From de3a96e3b12a4450c54eda6a81cc8d9afe7a7b8c Mon Sep 17 00:00:00 2001
From: Mark Johnston <markj@FreeBSD.org>
Date: Mon, 15 May 2017 21:44:40 +0000
Subject: [PATCH] Ensure that profile and tick probes provide a non-zero PC
 value.

The idle thread may process callouts while reloading the timer in
cpu_activeclock(). In this case, provide a representative value, &cpu_idle,
instead of 0 for args[0] so that the active thread can be more easily
identified from the probe.

This addresses intermittent failures of the profile-n/tst.argtest.d test.

MFC after:	2 weeks
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D10651
---
 sys/cddl/dev/profile/profile.c | 62 ++++++++++++++--------------------
 1 file changed, 25 insertions(+), 37 deletions(-)

diff --git a/sys/cddl/dev/profile/profile.c b/sys/cddl/dev/profile/profile.c
index 3b584246d14e..55ea9850e26d 100644
--- a/sys/cddl/dev/profile/profile.c
+++ b/sys/cddl/dev/profile/profile.c
@@ -266,37 +266,43 @@ sbt_to_nsec(sbintime_t sbt)
 }
 
 static void
-profile_fire(void *arg)
+profile_probe(profile_probe_t *prof, hrtime_t late)
 {
-	profile_probe_percpu_t *pcpu = arg;
-	profile_probe_t *prof = pcpu->profc_probe;
-	hrtime_t late;
+	struct thread *td;
 	struct trapframe *frame;
 	uintfptr_t pc, upc;
 
-#ifdef illumos
-	late = gethrtime() - pcpu->profc_expected;
-#else
-	late = sbt_to_nsec(sbinuptime() - pcpu->profc_expected);
-#endif
-
-	pc = 0;
-	upc = 0;
+	td = curthread;
+	pc = upc = 0;
 
 	/*
-	 * td_intr_frame can be unset if this is a catch up event
-	 * after waking up from idle sleep.
-	 * This can only happen on a CPU idle thread.
+	 * td_intr_frame can be unset if this is a catch-up event upon waking up
+	 * from idle sleep. This can only happen on a CPU idle thread. Use a
+	 * representative arg0 value in this case so that one of the probe
+	 * arguments is non-zero.
 	 */
-	frame = curthread->td_intr_frame;
+	frame = td->td_intr_frame;
 	if (frame != NULL) {
 		if (TRAPF_USERMODE(frame))
 			upc = TRAPF_PC(frame);
 		else
 			pc = TRAPF_PC(frame);
-	}
-	dtrace_probe(prof->prof_id, pc, upc, late, 0, 0);
+	} else if (TD_IS_IDLETHREAD(td))
+		pc = (uintfptr_t)&cpu_idle;
 
+	dtrace_probe(prof->prof_id, pc, upc, late, 0, 0);
+}
+
+static void
+profile_fire(void *arg)
+{
+	profile_probe_percpu_t *pcpu = arg;
+	profile_probe_t *prof = pcpu->profc_probe;
+	hrtime_t late;
+
+	late = sbt_to_nsec(sbinuptime() - pcpu->profc_expected);
+
+	profile_probe(prof, late);
 	pcpu->profc_expected += pcpu->profc_interval;
 	callout_schedule_sbt_curcpu(&pcpu->profc_cyclic,
 	    pcpu->profc_expected, 0, C_DIRECT_EXEC | C_ABSOLUTE);
@@ -306,26 +312,8 @@ static void
 profile_tick(void *arg)
 {
 	profile_probe_t *prof = arg;
-	struct trapframe *frame;
-	uintfptr_t pc, upc;
-
-	pc = 0;
-	upc = 0;
-
-	/*
-	 * td_intr_frame can be unset if this is a catch up event
-	 * after waking up from idle sleep.
-	 * This can only happen on a CPU idle thread.
-	 */
-	frame = curthread->td_intr_frame;
-	if (frame != NULL) {
-		if (TRAPF_USERMODE(frame))
-			upc = TRAPF_PC(frame);
-		else
-			pc = TRAPF_PC(frame);
-	}
-	dtrace_probe(prof->prof_id, pc, upc, 0, 0, 0);
 
+	profile_probe(prof, 0);
 	prof->prof_expected += prof->prof_interval;
 	callout_schedule_sbt(&prof->prof_cyclic,
 	    prof->prof_expected, 0, C_DIRECT_EXEC | C_ABSOLUTE);