runtime: fix iterator returns map entries after clear (pre-swissmap)

Fixes #70189
Fixes #59411

Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest-noswissmap
Change-Id: I4ef7ecd7e996330189309cb2a658cf34bf9e1119
Reviewed-on: https://go-review.googlesource.com/c/go/+/625275
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

2 files changed, 10 insertions, 22 deletions

diff --git a/src/runtime/map_noswiss.go b/src/runtime/map_noswiss.go
index d7b8a5fe11..327f0c81e8 100644
--- a/src/runtime/map_noswiss.go
+++ b/src/runtime/map_noswiss.go
@@ -123,6 +123,7 @@ type hmap struct {
 	buckets    unsafe.Pointer // array of 2^B Buckets. may be nil if count==0.
 	oldbuckets unsafe.Pointer // previous bucket array of half the size, non-nil only when growing
 	nevacuate  uintptr        // progress counter for evacuation (buckets less than this have been evacuated)
+	clearSeq   uint64
 
 	extra *mapextra // optional fields
 }
@@ -176,6 +177,7 @@ type hiter struct {
 	i           uint8
 	bucket      uintptr
 	checkBucket uintptr
+	clearSeq    uint64
 }
 
 // bucketShift returns 1<<b, optimized for code generation.
@@ -887,10 +889,11 @@ func mapiterinit(t *maptype, h *hmap, it *hiter) {
 		return
 	}
 
-	if unsafe.Sizeof(hiter{})/goarch.PtrSize != 12 {
+	if unsafe.Sizeof(hiter{}) != 8+12*goarch.PtrSize {
 		throw("hash_iter size incorrect") // see cmd/compile/internal/reflectdata/reflect.go
 	}
 	it.h = h
+	it.clearSeq = h.clearSeq
 
 	// grab snapshot of bucket state
 	it.B = h.B
@@ -1022,8 +1025,9 @@ next:
 				}
 			}
 		}
-		if (b.tophash[offi] != evacuatedX && b.tophash[offi] != evacuatedY) ||
-			!(t.ReflexiveKey() || t.Key.Equal(k, k)) {
+		if it.clearSeq == h.clearSeq &&
+			((b.tophash[offi] != evacuatedX && b.tophash[offi] != evacuatedY) ||
+				!(t.ReflexiveKey() || t.Key.Equal(k, k))) {
 			// This is the golden data, we can return it.
 			// OR
 			// key!=key, so the entry can't be deleted or updated, so we can just return it.
@@ -1079,28 +1083,12 @@ func mapclear(t *maptype, h *hmap) {
 	}
 
 	h.flags ^= hashWriting
-
-	// Mark buckets empty, so existing iterators can be terminated, see issue #59411.
-	markBucketsEmpty := func(bucket unsafe.Pointer, mask uintptr) {
-		for i := uintptr(0); i <= mask; i++ {
-			b := (*bmap)(add(bucket, i*uintptr(t.BucketSize)))
-			for ; b != nil; b = b.overflow(t) {
-				for i := uintptr(0); i < abi.OldMapBucketCount; i++ {
-					b.tophash[i] = emptyRest
-				}
-			}
-		}
-	}
-	markBucketsEmpty(h.buckets, bucketMask(h.B))
-	if oldBuckets := h.oldbuckets; oldBuckets != nil {
-		markBucketsEmpty(oldBuckets, h.oldbucketmask())
-	}
-
 	h.flags &^= sameSizeGrow
 	h.oldbuckets = nil
 	h.nevacuate = 0
 	h.noverflow = 0
 	h.count = 0
+	h.clearSeq++
 
 	// Reset the hash seed to make it more difficult for attackers to
 	// repeatedly trigger hash collisions. See issue 25237.
diff --git a/src/runtime/map_noswiss_test.go b/src/runtime/map_noswiss_test.go
index bda448471c..5af7b7b8c8 100644
--- a/src/runtime/map_noswiss_test.go
+++ b/src/runtime/map_noswiss_test.go
@@ -17,8 +17,8 @@ import (
 func TestHmapSize(t *testing.T) {
 	// The structure of hmap is defined in runtime/map.go
 	// and in cmd/compile/internal/reflectdata/map.go and must be in sync.
-	// The size of hmap should be 48 bytes on 64 bit and 28 bytes on 32 bit platforms.
-	var hmapSize = uintptr(8 + 5*goarch.PtrSize)
+	// The size of hmap should be 56 bytes on 64 bit and 36 bytes on 32 bit platforms.
+	var hmapSize = uintptr(2*8 + 5*goarch.PtrSize)
 	if runtime.RuntimeHmapSize != hmapSize {
 		t.Errorf("sizeof(runtime.hmap{})==%d, want %d", runtime.RuntimeHmapSize, hmapSize)
 	}