From 5dcedd65504cc9cadc9a5ea8bc3af51a26eec704 Mon Sep 17 00:00:00 2001
From: Damien Neil <dneil@google.com>
Date: Tue, 26 Aug 2025 13:26:57 -0700
Subject: runtime: lock mheap_.speciallock when allocating synctest specials

Avoid racing use of mheap_.specialBubbleAlloc.

Fixes #75134

Change-Id: I0c9140c18d2bca1e1c3387cd81230f0e8c9ac23e
Reviewed-on: https://go-review.googlesource.com/c/go/+/699255
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
---
 src/runtime/synctest.go | 2 ++
 1 file changed, 2 insertions(+)

(limited to 'src/runtime')

diff --git a/src/runtime/synctest.go b/src/runtime/synctest.go
index 16af1209b4..529f69fd93 100644
--- a/src/runtime/synctest.go
+++ b/src/runtime/synctest.go
@@ -410,7 +410,9 @@ func getOrSetBubbleSpecial(p unsafe.Pointer, bubbleid uint64, add bool) (assoc i
 	} else if add {
 		// p is not associated with a bubble,
 		// and we've been asked to add an association.
+		lock(&mheap_.speciallock)
 		s := (*specialBubble)(mheap_.specialBubbleAlloc.alloc())
+		unlock(&mheap_.speciallock)
 		s.bubbleid = bubbleid
 		s.special.kind = _KindSpecialBubble
 		s.special.offset = offset
-- 
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