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runtime: avoid overflow in mutex delay calculation

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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>
This commit is contained in:
Rhys Hiltner 2025-05-08 10:59:18 -07:00 • committed by Gopher Robot
parent 60d3bcdec3
commit ac645eaa0e
1 changed files with 1 additions and 1 deletions
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2
src/runtime/lock_spinbit.go
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@ -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))