runtime: fix off-by-1 error on address ranges

When growing the address ranges, the new length is the old length + 1.

Fixes #36113.

Change-Id: I1b425f78e473cfa3cbdfe6113e166663f41fc9f3
Reviewed-on: https://go-review.googlesource.com/c/go/+/211157
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

src/runtime/mpagealloc_test.go

@@ -112,6 +112,55 @@ func TestPageAllocGrow(t *testing.T) {
 				{PageBase(BaseChunkIdx+0x21, 0), PageBase(BaseChunkIdx+0x22, 0)},
 			},
 		},
+		"ManyDiscontiguous": {
+			// The initial cap is 16. Test 33 ranges, to exercise the growth path (twice).
+			chunks: []ChunkIdx{
+				BaseChunkIdx, BaseChunkIdx + 2, BaseChunkIdx + 4, BaseChunkIdx + 6,
+				BaseChunkIdx + 8, BaseChunkIdx + 10, BaseChunkIdx + 12, BaseChunkIdx + 14,
+				BaseChunkIdx + 16, BaseChunkIdx + 18, BaseChunkIdx + 20, BaseChunkIdx + 22,
+				BaseChunkIdx + 24, BaseChunkIdx + 26, BaseChunkIdx + 28, BaseChunkIdx + 30,
+				BaseChunkIdx + 32, BaseChunkIdx + 34, BaseChunkIdx + 36, BaseChunkIdx + 38,
+				BaseChunkIdx + 40, BaseChunkIdx + 42, BaseChunkIdx + 44, BaseChunkIdx + 46,
+				BaseChunkIdx + 48, BaseChunkIdx + 50, BaseChunkIdx + 52, BaseChunkIdx + 54,
+				BaseChunkIdx + 56, BaseChunkIdx + 58, BaseChunkIdx + 60, BaseChunkIdx + 62,
+				BaseChunkIdx + 64,
+			},
+			inUse: []AddrRange{
+				{PageBase(BaseChunkIdx, 0), PageBase(BaseChunkIdx+1, 0)},
+				{PageBase(BaseChunkIdx+2, 0), PageBase(BaseChunkIdx+3, 0)},
+				{PageBase(BaseChunkIdx+4, 0), PageBase(BaseChunkIdx+5, 0)},
+				{PageBase(BaseChunkIdx+6, 0), PageBase(BaseChunkIdx+7, 0)},
+				{PageBase(BaseChunkIdx+8, 0), PageBase(BaseChunkIdx+9, 0)},
+				{PageBase(BaseChunkIdx+10, 0), PageBase(BaseChunkIdx+11, 0)},
+				{PageBase(BaseChunkIdx+12, 0), PageBase(BaseChunkIdx+13, 0)},
+				{PageBase(BaseChunkIdx+14, 0), PageBase(BaseChunkIdx+15, 0)},
+				{PageBase(BaseChunkIdx+16, 0), PageBase(BaseChunkIdx+17, 0)},
+				{PageBase(BaseChunkIdx+18, 0), PageBase(BaseChunkIdx+19, 0)},
+				{PageBase(BaseChunkIdx+20, 0), PageBase(BaseChunkIdx+21, 0)},
+				{PageBase(BaseChunkIdx+22, 0), PageBase(BaseChunkIdx+23, 0)},
+				{PageBase(BaseChunkIdx+24, 0), PageBase(BaseChunkIdx+25, 0)},
+				{PageBase(BaseChunkIdx+26, 0), PageBase(BaseChunkIdx+27, 0)},
+				{PageBase(BaseChunkIdx+28, 0), PageBase(BaseChunkIdx+29, 0)},
+				{PageBase(BaseChunkIdx+30, 0), PageBase(BaseChunkIdx+31, 0)},
+				{PageBase(BaseChunkIdx+32, 0), PageBase(BaseChunkIdx+33, 0)},
+				{PageBase(BaseChunkIdx+34, 0), PageBase(BaseChunkIdx+35, 0)},
+				{PageBase(BaseChunkIdx+36, 0), PageBase(BaseChunkIdx+37, 0)},
+				{PageBase(BaseChunkIdx+38, 0), PageBase(BaseChunkIdx+39, 0)},
+				{PageBase(BaseChunkIdx+40, 0), PageBase(BaseChunkIdx+41, 0)},
+				{PageBase(BaseChunkIdx+42, 0), PageBase(BaseChunkIdx+43, 0)},
+				{PageBase(BaseChunkIdx+44, 0), PageBase(BaseChunkIdx+45, 0)},
+				{PageBase(BaseChunkIdx+46, 0), PageBase(BaseChunkIdx+47, 0)},
+				{PageBase(BaseChunkIdx+48, 0), PageBase(BaseChunkIdx+49, 0)},
+				{PageBase(BaseChunkIdx+50, 0), PageBase(BaseChunkIdx+51, 0)},
+				{PageBase(BaseChunkIdx+52, 0), PageBase(BaseChunkIdx+53, 0)},
+				{PageBase(BaseChunkIdx+54, 0), PageBase(BaseChunkIdx+55, 0)},
+				{PageBase(BaseChunkIdx+56, 0), PageBase(BaseChunkIdx+57, 0)},
+				{PageBase(BaseChunkIdx+58, 0), PageBase(BaseChunkIdx+59, 0)},
+				{PageBase(BaseChunkIdx+60, 0), PageBase(BaseChunkIdx+61, 0)},
+				{PageBase(BaseChunkIdx+62, 0), PageBase(BaseChunkIdx+63, 0)},
+				{PageBase(BaseChunkIdx+64, 0), PageBase(BaseChunkIdx+65, 0)},
+			},
+		},
 	}
 	if PageAlloc64Bit != 0 {
 		tests["ExtremelyDiscontiguous"] = test{

src/runtime/mranges.go

@@ -131,7 +131,7 @@ func (a *addrRanges) add(r addrRange) {
 			// assumptions), this would waste at most 4 MiB of memory.
 			oldRanges := a.ranges
 			ranges := (*notInHeapSlice)(unsafe.Pointer(&a.ranges))
-			ranges.len = len(oldRanges)
+			ranges.len = len(oldRanges) + 1
 			ranges.cap = cap(oldRanges) * 2
 			ranges.array = (*notInHeap)(persistentalloc(unsafe.Sizeof(addrRange{})*uintptr(ranges.cap), sys.PtrSize, a.sysStat))