panic: Decrementing non-positive ref count

goroutine 144 [running]:
gvisor.googlesource.com/gvisor/pkg/refs.(*AtomicRefCount).DecRefWithDestructor(0xc420492480, 0xc420173ca0)
	pkg/refs/refcounter.go:267 +0x1d9
gvisor.googlesource.com/gvisor/pkg/sentry/kernel/shm.(*Shm).DecRef(0xc420492480)
	pkg/sentry/kernel/shm/shm.go:373 +0x7a
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).removeVMAsLocked(0xc420162000, 0x10d7780, 0xc4204631e0, 0x10000, 0x7fffffff0000, 0xc420400070, 0xc42016205c)
	pkg/sentry/mm/vma.go:338 +0x308
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).unmapLocked(0xc420162000, 0x10d7780, 0xc4204631e0, 0x10000, 0x7fffffff0000, 0xc420173e68, 0xc4204631e0)
	pkg/sentry/mm/vma.go:310 +0x8c
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).DecUsers(0xc420162000, 0x10d7780, 0xc4204631e0)
	pkg/sentry/mm/lifecycle.go:220 +0x298
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*TaskContext).release(0xc420495930)
	pkg/sentry/kernel/task_context.go:62 +0xe6
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*runExitMain).execute(0x0, 0xc420495200, 0x10c84e0, 0x0)
	pkg/sentry/kernel/task_exit.go:261 +0x153
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).run(0xc420495200, 0x8)
	pkg/sentry/kernel/task_run.go:95 +0x265
created by gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).Start
	pkg/sentry/kernel/task_start.go:251 +0x194