panic: Incrementing non-positive ref count

goroutine 60435 [running]:
gvisor.googlesource.com/gvisor/pkg/refs.(*AtomicRefCount).IncRef(0xc420fea480)
	pkg/refs/refcounter.go:211 +0x5a
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).Fork(0xc420bcc000, 0xc7a780, 0xc420dd4000, 0x0, 0x0, 0x0)
	pkg/sentry/mm/lifecycle.go:90 +0x471
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*TaskContext).Fork(0xc420dd4730, 0xc7a780, 0xc420dd4000, 0x0, 0x0, 0x0, 0x0)
	pkg/sentry/kernel/task_context.go:89 +0x16d
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).Clone(0xc420dd4000, 0xc420e8bab0, 0x0, 0x0, 0x0, 0x0)
	pkg/sentry/kernel/task_clone.go:203 +0x1cc
gvisor.googlesource.com/gvisor/pkg/sentry/syscalls/linux.clone(0xc420dd4000, 0x24a000, 0x20000680, 0x20000780, 0x200007c0, 0x20000800, 0x40000002, 0x0, 0x997, 0x0)
	pkg/sentry/syscalls/linux/sys_thread.go:157 +0x21b
gvisor.googlesource.com/gvisor/pkg/sentry/syscalls/linux.Clone(0xc420dd4000, 0x24a000, 0x20000680, 0x20000780, 0x200007c0, 0x20000800, 0x0, 0x428854, 0xbe2cc0, 0xc420e8bc08, ...)
	pkg/sentry/syscalls/linux/sys_thread.go:171 +0x67
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).executeSyscall(0xc420dd4000, 0x38, 0x24a000, 0x20000680, 0x20000780, 0x200007c0, 0x20000800, 0x0, 0xc4202c21a0, 0xbb9f40, ...)
	pkg/sentry/kernel/task_syscall.go:162 +0x307
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallInvoke(0xc420dd4000, 0x38, 0x24a000, 0x20000680, 0x20000780, 0x200007c0, 0x20000800, 0x0, 0x20000800, 0x0)
	pkg/sentry/kernel/task_syscall.go:278 +0x62
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallEnter(0xc420dd4000, 0x38, 0x24a000, 0x20000680, 0x20000780, 0x200007c0, 0x20000800, 0x0, 0xc6d860, 0xc420e8be00)
	pkg/sentry/kernel/task_syscall.go:241 +0x91
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscall(0xc420dd4000, 0x2, 0xc4201217a0)
	pkg/sentry/kernel/task_syscall.go:216 +0x10c
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*runApp).execute(0x0, 0xc420dd4000, 0xc6d860, 0x0)
	pkg/sentry/kernel/task_run.go:217 +0xed8
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).run(0xc420dd4000, 0x81a)
	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:251 +0x100