panic: Incrementing non-positive ref count

goroutine 411934 [running]:
gvisor.googlesource.com/gvisor/pkg/refs.(*AtomicRefCount).IncRef(0xc420c8c840)
	pkg/refs/refcounter.go:211 +0x5a
gvisor.googlesource.com/gvisor/pkg/sentry/mm.vmaSetFunctions.Split(0x20fff000, 0x21003000, 0xc7ce80, 0xc420c8c840, 0x0, 0x101000101000101, 0x1, 0xc80080, 0xc420c8c840, 0x0, ...)
	pkg/sentry/mm/vma.go:388 +0x144
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*vmaSet).SplitUnchecked(0xc4209db970, 0xc4209db970, 0x7, 0x21000000, 0xc4209db970, 0x7, 0xc4209db970, 0x7)
	bazel-out/k8-fastbuild/bin/pkg/sentry/mm/vma_set.go:466 +0x180
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*vmaSet).Isolate(0xc4209db970, 0xc4209db970, 0x7, 0x20ffc000, 0x21000000, 0x7, 0x21000000)
	bazel-out/k8-fastbuild/bin/pkg/sentry/mm/vma_set.go:495 +0xe1
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).removeVMAsLocked(0xc4209db900, 0xc7ffc0, 0xc424ce8000, 0x20ffc000, 0x21000000, 0x67b3cd, 0xc421533af8)
	pkg/sentry/mm/vma.go:331 +0x12d
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).unmapLocked(0xc4209db900, 0xc7ffc0, 0xc424ce8000, 0x20ffc000, 0x21000000, 0x0, 0xab62)
	pkg/sentry/mm/vma.go:310 +0x7e
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).MUnmap(0xc4209db900, 0xc7ffc0, 0xc424ce8000, 0x20ffc000, 0x4000, 0x0, 0x0)
	pkg/sentry/mm/syscalls.go:262 +0xfe
gvisor.googlesource.com/gvisor/pkg/sentry/syscalls/linux.Munmap(0xc424ce8000, 0x20ffc000, 0x4000, 0x0, 0x0, 0x0, 0x0, 0x428854, 0xbe8108, 0xc421533c20, ...)
	pkg/sentry/syscalls/linux/sys_mmap.go:107 +0x5b
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).executeSyscall(0xc424ce8000, 0xb, 0x20ffc000, 0x4000, 0x0, 0x0, 0x0, 0x0, 0xc4202ca1e0, 0xbbf200, ...)
	pkg/sentry/kernel/task_syscall.go:162 +0x307
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallInvoke(0xc424ce8000, 0xb, 0x20ffc000, 0x4000, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0)
	pkg/sentry/kernel/task_syscall.go:278 +0x62
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallEnter(0xc424ce8000, 0xb, 0x20ffc000, 0x4000, 0x0, 0x0, 0x0, 0x0, 0xc730a0, 0xc421533e18)
	pkg/sentry/kernel/task_syscall.go:241 +0x91
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscall(0xc424ce8000, 0x2, 0xc4202907e0)
	pkg/sentry/kernel/task_syscall.go:216 +0x10c
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*runApp).execute(0x0, 0xc424ce8000, 0xc730a0, 0x0)
	pkg/sentry/kernel/task_run.go:217 +0xe56
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).run(0xc424ce8000, 0x30ff)
	pkg/sentry/kernel/task_run.go:95 +0x174
created by gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).Start
	pkg/sentry/kernel/task_start.go:258 +0x100