panic: Incrementing non-positive ref count

goroutine 1674495 [running]:
gvisor.googlesource.com/gvisor/pkg/refs.(*AtomicRefCount).IncRef(0xc4201e8a80)
	pkg/refs/refcounter.go:215 +0x5a
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).Fork(0xc420156580, 0xc7e8a0, 0xc420f82000, 0x0, 0x0, 0x0)
	pkg/sentry/mm/lifecycle.go:90 +0x471
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*TaskContext).Fork(0xc420f82730, 0xc7e8a0, 0xc420f82000, 0x0, 0xc4205c2910, 0x713df5, 0xc420156580)
	pkg/sentry/kernel/task_context.go:89 +0x16d
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).Clone(0xc420f82000, 0xc420973ac8, 0x0, 0x0, 0x0, 0x0)
	pkg/sentry/kernel/task_clone.go:203 +0x1b1
gvisor.googlesource.com/gvisor/pkg/sentry/syscalls/linux.clone(0xc420f82000, 0x400, 0x20001600, 0x20001700, 0x20001740, 0x20001780, 0x40000002, 0x0, 0x1d7e, 0x0)
	pkg/sentry/syscalls/linux/sys_thread.go:157 +0x21b
gvisor.googlesource.com/gvisor/pkg/sentry/syscalls/linux.Clone(0xc420f82000, 0x400, 0x20001600, 0x20001700, 0x20001740, 0x20001780, 0x0, 0x428854, 0xbe69d8, 0xc4205c2c20, ...)
	pkg/sentry/syscalls/linux/sys_thread.go:171 +0x67
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).executeSyscall(0xc420f82000, 0x38, 0x400, 0x20001600, 0x20001700, 0x20001740, 0x20001780, 0x0, 0xc4202ca200, 0xbbdd80, ...)
	pkg/sentry/kernel/task_syscall.go:162 +0x307
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallInvoke(0xc420f82000, 0x38, 0x400, 0x20001600, 0x20001700, 0x20001740, 0x20001780, 0x0, 0x20001780, 0x0)
	pkg/sentry/kernel/task_syscall.go:278 +0x62
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallEnter(0xc420f82000, 0x38, 0x400, 0x20001600, 0x20001700, 0x20001740, 0x20001780, 0x0, 0xc71920, 0xc4205c2e18)
	pkg/sentry/kernel/task_syscall.go:241 +0x91
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscall(0xc420f82000, 0x2, 0xc4202907e0)
	pkg/sentry/kernel/task_syscall.go:216 +0x10c
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*runApp).execute(0x0, 0xc420f82000, 0xc71920, 0x0)
	pkg/sentry/kernel/task_run.go:217 +0xe56
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).run(0xc420f82000, 0x1e60)
	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