From: Michael Anthony Knyszek <mknyszek@google.com>
Date: Wed, 9 Oct 2024 17:38:49 +0000 (+0000)
Subject: runtime: execute publicationBarrier in noscan case for delayed zeroing
X-Git-Tag: go1.24rc1~665
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=acd072a0784863dfbdf32da9d770753722270a26;p=gostls13.git

runtime: execute publicationBarrier in noscan case for delayed zeroing

This is a peace-of-mind change to make sure that delayed-zeroed memory
(in the large alloc case) is globally visible from the moment the
allocation is published back to the caller.

The way it's written right now is good enough for the garbage collector
(we already have a publication barrier for a nil span.largeType, so the
GC will ignore the noscan span) but this might matter for user code on
weak memory architectures.

Change-Id: I06ac9b95863074e5f09382629083b19bfa87fdb8
Reviewed-on: https://go-review.googlesource.com/c/go/+/619036
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
---

diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index 3416b599f9..83f7f64f6f 100644
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -1581,14 +1581,13 @@ func mallocgcLarge(size uintptr, typ *_type, needzero bool) (unsafe.Pointer, uin
 		memclrNoHeapPointersChunked(size, x) // This is a possible preemption point: see #47302
 
 		// Finish storing the type information for this case.
+		mp := acquirem()
 		if !noscan {
-			mp := acquirem()
 			getMCache(mp).scanAlloc += heapSetTypeLarge(uintptr(x), size, typ, span)
-
-			// Publish the type information with the zeroed memory.
-			publicationBarrier()
-			releasem(mp)
 		}
+		// Publish the object with the now-zeroed memory.
+		publicationBarrier()
+		releasem(mp)
 	}
 	return x, size
 }