panic: Incrementing non-positive ref count

goroutine 190016 [running]:
gvisor.googlesource.com/gvisor/pkg/refs.(*AtomicRefCount).IncRef(0xc4203e3b00)
	pkg/refs/refcounter.go:211 +0x5a
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).Sync(0xc420d12000, 0xc75800, 0xc420db2900, 0x20ffa000, 0x4000, 0xc420c2db70, 0x40000002)
	pkg/sentry/mm/syscalls.go:768 +0x1fb
gvisor.googlesource.com/gvisor/pkg/sentry/syscalls/linux.Msync(0xc420db2900, 0x20ffa000, 0x4000, 0x4, 0x0, 0x0, 0x0, 0x428854, 0xbde328, 0xc420c2dc08, ...)
	pkg/sentry/syscalls/linux/sys_mmap.go:419 +0x1c4
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).executeSyscall(0xc420db2900, 0x1a, 0x20ffa000, 0x4000, 0x4, 0x0, 0x0, 0x0, 0xc42000a3c0, 0xbb5a60, ...)
	pkg/sentry/kernel/task_syscall.go:162 +0x307
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallInvoke(0xc420db2900, 0x1a, 0x20ffa000, 0x4000, 0x4, 0x0, 0x0, 0x0, 0x0, 0x0)
	pkg/sentry/kernel/task_syscall.go:278 +0x62
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallEnter(0xc420db2900, 0x1a, 0x20ffa000, 0x4000, 0x4, 0x0, 0x0, 0x0, 0xc689e0, 0xc420c2de00)
	pkg/sentry/kernel/task_syscall.go:241 +0x91
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscall(0xc420db2900, 0x2, 0xc4203d46c0)
	pkg/sentry/kernel/task_syscall.go:216 +0x10c
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*runApp).execute(0x0, 0xc420db2900, 0xc689e0, 0x0)
	pkg/sentry/kernel/task_run.go:217 +0xed8
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).run(0xc420db2900, 0x1ab9)
	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