寻求解答go slice 并发append问题

众所周知，go slice append是非线程安全的。写了一下demo：

func main() {
    for {
       var errs []error
       go func() { errs = append(errs, nil) }()
       go func() { errs = append(errs, nil) }()
    }
}

用go1.20.14 darwin/arm64运行下，很快就抛出错误:

panic: runtime error: invalid memory address or nil pointer dereference

在debug模式下运行，panic的线程堆栈：

但是发现同一个栈上竟然有两个growslice。然后看每个growslice的变量值：

看growslice的源码：

func growslice(oldPtr unsafe.Pointer, newLen, oldCap, num int, et *_type) slice {
    oldLen := newLen - num
    if raceenabled {
       callerpc := getcallerpc()
       racereadrangepc(oldPtr, uintptr(oldLen*int(et.size)), callerpc, abi.FuncPCABIInternal(growslice))
    }
    if msanenabled {
       msanread(oldPtr, uintptr(oldLen*int(et.size)))
    }
    if asanenabled {
       asanread(oldPtr, uintptr(oldLen*int(et.size)))
    }

    if newLen < 0 {
       panic(errorString("growslice: len out of range"))
    }

    if et.size == 0 {
       // append should not create a slice with nil pointer but non-zero len.
       // We assume that append doesn't need to preserve oldPtr in this case.
       return slice{unsafe.Pointer(&zerobase), newLen, newLen}
    }

    newcap := oldCap
    doublecap := newcap + newcap
    if newLen > doublecap {
       newcap = newLen
    } else {
       const threshold = 256
       if oldCap < threshold {
          newcap = doublecap
       } else {
          // Check 0 < newcap to detect overflow
          // and prevent an infinite loop.
          for 0 < newcap && newcap < newLen {
             // Transition from growing 2x for small slices
             // to growing 1.25x for large slices. This formula
             // gives a smooth-ish transition between the two.
             newcap += (newcap + 3*threshold) / 4
          }
          // Set newcap to the requested cap when
          // the newcap calculation overflowed.
          if newcap <= 0 {
             newcap = newLen
          }
       }
    }

    var overflow bool
    var lenmem, newlenmem, capmem uintptr
    // Specialize for common values of et.size.
    // For 1 we don't need any division/multiplication.
    // For goarch.PtrSize, compiler will optimize division/multiplication into a shift by a constant.
    // For powers of 2, use a variable shift.
    switch {
    case et.size == 1:
       lenmem = uintptr(oldLen)
       newlenmem = uintptr(newLen)
       capmem = roundupsize(uintptr(newcap))
       overflow = uintptr(newcap) > maxAlloc
       newcap = int(capmem)
    case et.size == goarch.PtrSize:
       lenmem = uintptr(oldLen) * goarch.PtrSize
       newlenmem = uintptr(newLen) * goarch.PtrSize
       capmem = roundupsize(uintptr(newcap) * goarch.PtrSize)
       overflow = uintptr(newcap) > maxAlloc/goarch.PtrSize
       newcap = int(capmem / goarch.PtrSize)
    case isPowerOfTwo(et.size):
       var shift uintptr
       if goarch.PtrSize == 8 {
          // Mask shift for better code generation.
          shift = uintptr(sys.TrailingZeros64(uint64(et.size))) & 63
       } else {
          shift = uintptr(sys.TrailingZeros32(uint32(et.size))) & 31
       }
       lenmem = uintptr(oldLen) << shift
       newlenmem = uintptr(newLen) << shift
       capmem = roundupsize(uintptr(newcap) << shift)
       overflow = uintptr(newcap) > (maxAlloc >> shift)
       newcap = int(capmem >> shift)
       capmem = uintptr(newcap) << shift
    default:
       lenmem = uintptr(oldLen) * et.size
       newlenmem = uintptr(newLen) * et.size
       capmem, overflow = math.MulUintptr(et.size, uintptr(newcap))
       capmem = roundupsize(capmem)
       newcap = int(capmem / et.size)
       capmem = uintptr(newcap) * et.size
    }

    // The check of overflow in addition to capmem > maxAlloc is needed
    // to prevent an overflow which can be used to trigger a segfault
    // on 32bit architectures with this example program:
    //
    // type T [1<<27 + 1]int64
    //
    // var d T
    // var s []T
    //
    // func main() {
    //   s = append(s, d, d, d, d)
    //   print(len(s), "\n")
    // }
    if overflow || capmem > maxAlloc {
       panic(errorString("growslice: len out of range"))
    }

    var p unsafe.Pointer
    if et.ptrdata == 0 {
       p = mallocgc(capmem, nil, false)
       // The append() that calls growslice is going to overwrite from oldLen to newLen.
       // Only clear the part that will not be overwritten.
       // The reflect_growslice() that calls growslice will manually clear
       // the region not cleared here.
       memclrNoHeapPointers(add(p, newlenmem), capmem-newlenmem)
    } else {
       // Note: can't use rawmem (which avoids zeroing of memory), because then GC can scan uninitialized memory.
       p = mallocgc(capmem, et, true)
       if lenmem > 0 && writeBarrier.enabled {
          // Only shade the pointers in oldPtr since we know the destination slice p
          // only contains nil pointers because it has been cleared during alloc.
          bulkBarrierPreWriteSrcOnly(uintptr(p), uintptr(oldPtr), lenmem-et.size+et.ptrdata)
       }
    }
    memmove(p, oldPtr, lenmem)

    return slice{p, newLen, newcap}
}

oldlen是局部变量,然后lenmem是oldlen乘过来的，但是堆栈图里的lenmem和oldlen值却毫无关系。例如下面的growslice中，oldlen=0, 那lenmem结果也应该是0， 却变成了一个大数。

恳请大神帮忙答疑下，谢谢。