runtime: memlock not unlocked in all control flow paths in sysReserveAlignedSbrk

[tschneidereit]

Go version

go version go1.24.4 darwin/arm64

Output of go env in your module/workspace:

N/A

What did you do?

While I ran into the issue in real code, it's somewhat obscure and impossible to reproduce using https://go.dev/play, since it requires passing -ldflags=-checklinkname=0 to go build.

In short, I called sysReserveAlignedSbrk(65536, 0) twice.

What did you see happen?

The lock taken here wasn't released during the first call, because this return is hit, leading to a panic in the second call.

What did you expect to see?

The lock to always be released, presumably by adding unlock(&memlock) before each return.

It's not clear to me whether this is reachable without pull-mode linking of sysReserveAlignedSbrk or sysReserveAligned, since the former is only called by the latter, and the latter seems unused—but I might certainly be missing usages of either or both.

[gabyhelp]

Related Code Changes

• runtime: add missing unlock in sysReserveAlignedSbrk

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[gopherbot]

Change https://go.dev/cl/683295 mentions this issue: runtime: add missing unlock in sysReserveAlignedSbrk

[cherrymui]

@gopherbot please backport this to Go 1.24. This could potentially cause a deadlock. The fix is obviously safe. Thanks.

(1.24 only as sysReserveAlignedSbrk is new code in 1.24.)

[gopherbot]

Backport issue(s) opened: #74346 (for 1.24).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.