From ee92daae25029882979eb694bd7246491e364d3c Mon Sep 17 00:00:00 2001
From: Meng Zhuo <mzh@golangcn.org>
Date: Mon, 20 Sep 2021 20:44:50 +0800
Subject: [PATCH] runtime: ensure at least 1 tick between events

ticks might be same after tick division, although the real cputicks
is linear growth

Fixes #46737

Change-Id: I1d98866fbf21b426c6c1c96cc9cf802d7f440f18
Reviewed-on: https://go-review.googlesource.com/c/go/+/330849
Trust: Meng Zhuo <mzh@golangcn.org>
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Meng Zhuo <mzh@golangcn.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
---
 src/runtime/trace.go | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/runtime/trace.go b/src/runtime/trace.go
index 00544e4283c..5b14a5f5539 100644
--- a/src/runtime/trace.go
+++ b/src/runtime/trace.go
@@ -551,8 +551,15 @@ func traceEventLocked(extraBytes int, mp *m, pid int32, bufp *traceBufPtr, ev by
 		bufp.set(buf)
 	}
 
+	// NOTE: ticks might be same after tick division, although the real cputicks is
+	// linear growth.
 	ticks := uint64(cputicks()) / traceTickDiv
 	tickDiff := ticks - buf.lastTicks
+	if tickDiff == 0 {
+		ticks = buf.lastTicks + 1
+		tickDiff = 1
+	}
+
 	buf.lastTicks = ticks
 	narg := byte(len(args))
 	if skip >= 0 {
@@ -653,6 +660,9 @@ func traceFlush(buf traceBufPtr, pid int32) traceBufPtr {
 
 	// initialize the buffer for a new batch
 	ticks := uint64(cputicks()) / traceTickDiv
+	if ticks == bufp.lastTicks {
+		ticks = bufp.lastTicks + 1
+	}
 	bufp.lastTicks = ticks
 	bufp.byte(traceEvBatch | 1<<traceArgCountShift)
 	bufp.varint(uint64(pid))