panic: Incrementing non-positive ref count

goroutine 6021041 [running]:
gvisor.googlesource.com/gvisor/pkg/refs.(*AtomicRefCount).IncRef(0xc4204e7c80)
	pkg/refs/refcounter.go:215 +0x5a
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).Fork(0xc4207e4580, 0xc62220, 0xc42264e000, 0x0, 0x0, 0x0)
	pkg/sentry/mm/lifecycle.go:90 +0x471
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*TaskContext).Fork(0xc42264e730, 0xc62220, 0xc42264e000, 0x0, 0x10b7e60, 0x0, 0x0)
	pkg/sentry/kernel/task_context.go:91 +0x16d
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).Clone(0xc42264e000, 0xc422de9ab8, 0x0, 0x0, 0x0, 0x0)
	pkg/sentry/kernel/task_clone.go:203 +0x1b1
gvisor.googlesource.com/gvisor/pkg/sentry/syscalls/linux.clone(0xc42264e000, 0x41200000, 0x20000000, 0x200000c0, 0x20000100, 0x20000140, 0x1c28, 0xc4205e0b88, 0x40000002, 0x0)
	pkg/sentry/syscalls/linux/sys_thread.go:157 +0x21b
gvisor.googlesource.com/gvisor/pkg/sentry/syscalls/linux.Clone(0xc42264e000, 0x41200000, 0x20000000, 0x200000c0, 0x20000100, 0x20000140, 0x0, 0x202, 0xc4205e0c10, 0x428854, ...)
	pkg/sentry/syscalls/linux/sys_thread.go:171 +0x67
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).executeSyscall(0xc42264e000, 0x38, 0x41200000, 0x20000000, 0x200000c0, 0x20000100, 0x20000140, 0x0, 0x0, 0xba1ec0, ...)
	pkg/sentry/kernel/task_syscall.go:162 +0x307
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallInvoke(0xc42264e000, 0x38, 0x41200000, 0x20000000, 0x200000c0, 0x20000100, 0x20000140, 0x0, 0x20000140, 0x0)
	pkg/sentry/kernel/task_syscall.go:280 +0x62
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallEnter(0xc42264e000, 0x38, 0x41200000, 0x20000000, 0x200000c0, 0x20000100, 0x20000140, 0x0, 0xc55020, 0x0)
	pkg/sentry/kernel/task_syscall.go:241 +0x91
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscall(0xc42264e000, 0x2, 0xc420343680)
	pkg/sentry/kernel/task_syscall.go:216 +0x142
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*runApp).execute(0x0, 0xc42264e000, 0xc55020, 0x0)
	pkg/sentry/kernel/task_run.go:219 +0xe56
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).run(0xc42264e000, 0x97a6)
	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