panic: Decrementing non-positive ref count

goroutine 3260321 [running]:
gvisor.googlesource.com/gvisor/pkg/refs.(*AtomicRefCount).DecRefWithDestructor(0xc42170c840, 0xc422757d58)
	pkg/refs/refcounter.go:271 +0x162
gvisor.googlesource.com/gvisor/pkg/sentry/kernel/shm.(*Shm).DecRef(0xc42170c840)
	pkg/sentry/kernel/shm/shm.go:373 +0x48
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).removeVMAsLocked(0xc422498000, 0xc82100, 0xc420703680, 0x1000, 0x7ffffffff000, 0x67c91d, 0xc422757e48)
	pkg/sentry/mm/vma.go:338 +0x1a4
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).unmapLocked(0xc422498000, 0xc82100, 0xc420703680, 0x1000, 0x7ffffffff000, 0x18, 0x200)
	pkg/sentry/mm/vma.go:310 +0x7e
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).DecUsers(0xc422498000, 0xc82100, 0xc420703680)
	pkg/sentry/mm/lifecycle.go:220 +0x1dd
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*TaskContext).release(0xc422f12b30)
	pkg/sentry/kernel/task_context.go:62 +0xd6
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*runExitMain).execute(0x0, 0xc422f12400, 0xc74ca0, 0x0)
	pkg/sentry/kernel/task_exit.go:261 +0xc5
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).run(0xc422f12400, 0x7d46)
	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