panic: Incrementing non-positive ref count

goroutine 4362674 [running]:
gvisor.googlesource.com/gvisor/pkg/refs.(*AtomicRefCount).IncRef(0xc4210a6c00)
	pkg/refs/refcounter.go:215 +0x5a
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).Fork(0xc42362a000, 0xc7faa0, 0xc424bc2900, 0x0, 0x0, 0x0)
	pkg/sentry/mm/lifecycle.go:90 +0x471
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*TaskContext).Fork(0xc424bc3030, 0xc7faa0, 0xc424bc2900, 0x693400, 0xc42401d2d0, 0xc4200f08f0, 0x427f59)
	pkg/sentry/kernel/task_context.go:89 +0x16d
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).Clone(0xc424bc2900, 0xc4211c3ac8, 0x0, 0x0, 0x0, 0x0)
	pkg/sentry/kernel/task_clone.go:203 +0x1b1
gvisor.googlesource.com/gvisor/pkg/sentry/syscalls/linux.clone(0xc424bc2900, 0x2000, 0x20000000, 0x20000100, 0x20000140, 0x20000180, 0x40000002, 0x0, 0x5fd2, 0x0)
	pkg/sentry/syscalls/linux/sys_thread.go:157 +0x21b
gvisor.googlesource.com/gvisor/pkg/sentry/syscalls/linux.Clone(0xc424bc2900, 0x2000, 0x20000000, 0x20000100, 0x20000140, 0x20000180, 0x0, 0x428854, 0xbe7b58, 0xc4200f0c20, ...)
	pkg/sentry/syscalls/linux/sys_thread.go:171 +0x67
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).executeSyscall(0xc424bc2900, 0x38, 0x2000, 0x20000000, 0x20000100, 0x20000140, 0x20000180, 0x0, 0xc42029c3a0, 0xbbeea0, ...)
	pkg/sentry/kernel/task_syscall.go:162 +0x307
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallInvoke(0xc424bc2900, 0x38, 0x2000, 0x20000000, 0x20000100, 0x20000140, 0x20000180, 0x0, 0x20000180, 0x0)
	pkg/sentry/kernel/task_syscall.go:278 +0x62
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallEnter(0xc424bc2900, 0x38, 0x2000, 0x20000000, 0x20000100, 0x20000140, 0x20000180, 0x0, 0xc72b20, 0xc4200f0e18)
	pkg/sentry/kernel/task_syscall.go:241 +0x91
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscall(0xc424bc2900, 0x2, 0xc42047a6c0)
	pkg/sentry/kernel/task_syscall.go:216 +0x10c
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*runApp).execute(0x0, 0xc424bc2900, 0xc72b20, 0x0)
	pkg/sentry/kernel/task_run.go:217 +0xe56
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).run(0xc424bc2900, 0x77dc)
	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