From ac645eaa0efc982eb238188a5f14835d2c1f8d18 Mon Sep 17 00:00:00 2001
From: Rhys Hiltner <rhys.hiltner@gmail.com>
Date: Thu, 8 May 2025 10:59:18 -0700
Subject: [PATCH] runtime: avoid overflow in mutex delay calculation
If cputicks is in the top quarter of the int64's range, adding two
values together will overflow and confuse the subsequent calculations,
leading to zero-duration contention events in the profile.
This fixes the TestRuntimeLockMetricsAndProfile failures on the
linux-s390x builder.
Change-Id: Icb814c39a8702379dfd71c06a53b2618e3589e07
Reviewed-on: https://go-review.googlesource.com/c/go/+/671115
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Rhys Hiltner <rhys.hiltner@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
---
src/runtime/lock_spinbit.go | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/runtime/lock_spinbit.go b/src/runtime/lock_spinbit.go
index c2a6c76629c..f90698a4c94 100644
--- a/src/runtime/lock_spinbit.go
+++ b/src/runtime/lock_spinbit.go
@@ -404,7 +404,7 @@ useStackLock:
n++
next := node.mWaitList.next.ptr()
if next == nil {
- cycles := endTicks - (head.mWaitList.startTicks+node.mWaitList.startTicks)/2
+ cycles := ((endTicks - head.mWaitList.startTicks) + (endTicks - node.mWaitList.startTicks)) / 2
node.mWaitList.startTicks = endTicks
head.mWaitList.startTicks = endTicks
getg().m.mLockProfile.recordUnlock(cycles * int64(n))
--
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