panic: kernfs.Dentry.DecRef() called without holding a reference

goroutine 251 [running]:
panic({0xf82ce0, 0x1368f68})
	GOROOT/src/runtime/panic.go:941 +0x397 fp=0xc002713198 sp=0xc0027130d8 pc=0x4358b7
gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs.(*Dentry).decRefLocked(0x967765?, {0x13831b0?, 0xc000a5b500?})
	pkg/sentry/fsimpl/kernfs/kernfs.go:302 +0xac fp=0xc0027131c0 sp=0xc002713198 pc=0x7dc26c
gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs.(*Dentry).releaseKeptDentriesLocked(0xc000d2f0e0, {0x13831b0, 0xc000a5b500})
	pkg/sentry/fsimpl/kernfs/filesystem.go:282 +0x98 fp=0xc0027132a0 sp=0xc0027131c0 pc=0x7cdb38
gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs.(*Dentry).releaseKeptDentriesLocked(0xc00219afc0, {0x13831b0, 0xc000a5b500})
	pkg/sentry/fsimpl/kernfs/filesystem.go:293 +0x245 fp=0xc002713380 sp=0xc0027132a0 pc=0x7cdce5
gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs.(*Filesystem).Release(0xc002968120, {0x13831b0, 0xc000a5b500})
	pkg/sentry/fsimpl/kernfs/filesystem.go:267 +0x7b fp=0xc0027133b8 sp=0xc002713380 pc=0x7cd9db
gvisor.dev/gvisor/pkg/sentry/fsimpl/cgroupfs.(*filesystem).Release(0xc002968120, {0x13831b0, 0xc000a5b500})
	pkg/sentry/fsimpl/cgroupfs/cgroupfs.go:474 +0x110 fp=0xc0027133e8 sp=0xc0027133b8 pc=0xc8f150
gvisor.dev/gvisor/pkg/sentry/vfs.(*Filesystem).DecRef.func1()
	pkg/sentry/vfs/filesystem.go:81 +0xbd fp=0xc002713428 sp=0xc0027133e8 pc=0x74eedd
gvisor.dev/gvisor/pkg/sentry/vfs.(*FilesystemRefs).DecRef(0xc000325501?, 0xc0027134a0)
	bazel-out/k8-fastbuild-ST-246649c541f7/bin/pkg/sentry/vfs/filesystem_refs.go:131 +0x7e fp=0xc002713490 sp=0xc002713428 pc=0x74f79e
gvisor.dev/gvisor/pkg/sentry/vfs.(*Filesystem).DecRef(0x0?, {0x13831b0?, 0xc000a5b500?})
	pkg/sentry/vfs/filesystem.go:77 +0x5b fp=0xc0027134d0 sp=0xc002713490 pc=0x74eddb
gvisor.dev/gvisor/pkg/sentry/vfs.(*Mount).destroy(0xc000532e00, {0x13831b0, 0xc000a5b500})
	pkg/sentry/vfs/mount.go:926 +0x16d fp=0xc002713520 sp=0xc0027134d0 pc=0x75936d
gvisor.dev/gvisor/pkg/sentry/vfs.(*Mount).DecRef(0xc000532e00, {0x13831b0, 0xc000a5b500})
	pkg/sentry/vfs/mount.go:910 +0xa5 fp=0xc002713548 sp=0xc002713520 pc=0x7591c5
gvisor.dev/gvisor/pkg/sentry/vfs.VirtualDentry.DecRef({0xc000532e00?, 0xc00219afc0?}, {0x13831b0, 0xc000a5b500})
	pkg/sentry/vfs/vfs.go:927 +0x6d fp=0xc002713578 sp=0xc002713548 pc=0x7686ad
gvisor.dev/gvisor/pkg/sentry/vfs.(*VirtualFilesystem).UmountAt.func1()
	pkg/sentry/vfs/mount.go:653 +0x36 fp=0xc0027135a8 sp=0xc002713578 pc=0x7586f6
runtime.deferreturn()
	GOROOT/src/runtime/panic.go:436 +0x33 fp=0xc0027135e8 sp=0xc0027135a8 pc=0x4349d3
gvisor.dev/gvisor/pkg/sentry/vfs.(*VirtualFilesystem).UmountAt(0xc0001641d0, {0x13831b0, 0xc000a5b500}, 0xc000646800?, 0xc0019a1700?, 0xc00271384c)
	pkg/sentry/vfs/mount.go:739 +0x945 fp=0xc0027137c0 sp=0xc0027135e8 pc=0x758305
gvisor.dev/gvisor/pkg/sentry/syscalls/linux.Umount2(0xc000a5b500, {{0x7f3ad1d8b580}, {0xa}, {0x7f3ad1d8b58b}, {0x55e5622fd7e3}, {0xffffffff}, {0x7f3ad1d8b350}})
	pkg/sentry/syscalls/linux/sys_mount.go:171 +0x326 fp=0xc002713958 sp=0xc0027137c0 pc=0xac72a6
gvisor.dev/gvisor/pkg/sentry/kernel.(*Task).executeSyscall(0xc000a5b500, 0xa6, {{0x7f3ad1d8b580}, {0xa}, {0x7f3ad1d8b58b}, {0x55e5622fd7e3}, {0xffffffff}, {0x7f3ad1d8b350}})
	pkg/sentry/kernel/task_syscall.go:142 +0x80b fp=0xc002713c98 sp=0xc002713958 pc=0x9766ab
gvisor.dev/gvisor/pkg/sentry/kernel.(*Task).doSyscallInvoke(0xc000a5b500, 0xc000c6c820?, {{0x7f3ad1d8b580}, {0xa}, {0x7f3ad1d8b58b}, {0x55e5622fd7e3}, {0xffffffff}, {0x7f3ad1d8b350}})
	pkg/sentry/kernel/task_syscall.go:322 +0x54 fp=0xc002713cf8 sp=0xc002713c98 pc=0x977c94
gvisor.dev/gvisor/pkg/sentry/kernel.(*Task).doSyscallEnter(0xc0002fc400?, 0xc002713e40?, {{0x7f3ad1d8b580}, {0xa}, {0x7f3ad1d8b58b}, {0x55e5622fd7e3}, {0xffffffff}, {0x7f3ad1d8b350}})
	pkg/sentry/kernel/task_syscall.go:282 +0x85 fp=0xc002713d58 sp=0xc002713cf8 pc=0x977885
gvisor.dev/gvisor/pkg/sentry/kernel.(*Task).doSyscall(0xc00083a2c0?)
	pkg/sentry/kernel/task_syscall.go:257 +0x3ac fp=0xc002713e50 sp=0xc002713d58 pc=0x97754c
gvisor.dev/gvisor/pkg/sentry/kernel.(*runApp).execute(0xc000a5b500?, 0xc000a5b500)
	pkg/sentry/kernel/task_run.go:253 +0x1125 fp=0xc002713f60 sp=0xc002713e50 pc=0x969465
gvisor.dev/gvisor/pkg/sentry/kernel.(*Task).run(0xc000a5b500, 0x33)
	pkg/sentry/kernel/task_run.go:94 +0x1ec fp=0xc002713fc0 sp=0xc002713f60 pc=0x967cac
gvisor.dev/gvisor/pkg/sentry/kernel.(*Task).Start.func1()
	pkg/sentry/kernel/task_start.go:378 +0x2a fp=0xc002713fe0 sp=0xc002713fc0 pc=0x974b4a
runtime.goexit()
	src/runtime/asm_amd64.s:1571 +0x1 fp=0xc002713fe8 sp=0xc002713fe0 pc=0x4695c1
created by gvisor.dev/gvisor/pkg/sentry/kernel.(*Task).Start
	pkg/sentry/kernel/task_start.go:378 +0x105