panic: Decrementing non-positive ref count

goroutine 1992448 [running]:
gvisor.googlesource.com/gvisor/pkg/refs.(*AtomicRefCount).DecRefWithDestructor(0xc4202a5680, 0xc420939d58)
	pkg/refs/refcounter.go:271 +0x162
gvisor.googlesource.com/gvisor/pkg/sentry/kernel/shm.(*Shm).DecRef(0xc4202a5680)
	pkg/sentry/kernel/shm/shm.go:377 +0x48
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).removeVMAsLocked(0xc420d86000, 0xc63900, 0xc42037b0c0, 0x10000, 0x7fffffff0000, 0x66d0fd, 0xc420939e48)
	pkg/sentry/mm/vma.go:338 +0x1a4
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).unmapLocked(0xc420d86000, 0xc63900, 0xc42037b0c0, 0x10000, 0x7fffffff0000, 0x18, 0xc4213b67c8)
	pkg/sentry/mm/vma.go:310 +0x7e
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).DecUsers(0xc420d86000, 0xc63900, 0xc42037b0c0)
	pkg/sentry/mm/lifecycle.go:220 +0x1dd
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*TaskContext).release(0xc420647430)
	pkg/sentry/kernel/task_context.go:64 +0xd6
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*runExitMain).execute(0x0, 0xc420646d00, 0xc56320, 0x0)
	pkg/sentry/kernel/task_exit.go:266 +0xc5
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).run(0xc420646d00, 0x3bb4)
	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