panic: interface conversion: refs.RefCounter is *fs.File, not *fs.Dirent

goroutine 206 [running]:
gvisor.dev/gvisor/pkg/sentry/fs.(*Dirent).walk(0xc00018cd10, 0xef0e60, 0xc00018f500, 0xc0005568f0, 0xc000165202, 0x3, 0xc00108b801, 0x6b7b2f, 0xc000349500, 0xef0e60)
	pkg/sentry/fs/dirent.go:486 +0xaf8
gvisor.dev/gvisor/pkg/sentry/fs.(*Dirent).Walk(0xc00018cd10, 0xef0e60, 0xc00018f500, 0xc0005568f0, 0xc000165202, 0x3, 0xc00018cd10, 0x0, 0x0)
	pkg/sentry/fs/dirent.go:613 +0xd9
gvisor.dev/gvisor/pkg/sentry/fs.(*MountNamespace).FindLink(0xc0005482a0, 0xef0e60, 0xc00018f500, 0xc0005568f0, 0xc00018cd10, 0xc000165200, 0x5, 0xc00108ba18, 0xc00108bf68, 0xc0008c62e8, ...)
	pkg/sentry/fs/mounts.go:522 +0x2d2
gvisor.dev/gvisor/pkg/sentry/fs.(*MountNamespace).FindInode(0xc0005482a0, 0xef0e60, 0xc00018f500, 0xc0005568f0, 0xc00018cd10, 0xc000165200, 0x5, 0xc00108ba18, 0x7f39b9219ac0, 0x1000, ...)
	pkg/sentry/fs/mounts.go:560 +0x71
gvisor.dev/gvisor/pkg/sentry/syscalls/linux.fileOpOn(0xc00018f500, 0xffffff9c, 0xc000165200, 0x5, 0x1, 0xc00108bae8, 0x0, 0x0)
	pkg/sentry/syscalls/linux/sys_file.go:96 +0x10f
gvisor.dev/gvisor/pkg/sentry/syscalls/linux.Umount2(0xc00018f500, 0x7f39b9219ac0, 0x2, 0xc, 0x0, 0xa69940, 0x0, 0x475d61, 0xede5, 0xc00108bb8c, ...)
	pkg/sentry/syscalls/linux/sys_mount.go:151 +0x137
DIAGNOSIS:
I0107 06:12:56.300453   31679 x:0] ***************************
I0107 06:12:56.300564   31679 x:0] Args: [/syzkaller/managers/ptrace-direct-overlay-host/current/image -root /syzkaller/managers/ptrace-direct-overlay-host/workdir/gvisor_root -watchdog-action=panic -network=none -debug -alsologtostderr -platform=ptrace -file-access=shared -network=host debug -stacks --ps ci-gvisor-ptrace-direct-overlay-host-0]
I0107 06:12:56.301050   31679 x:0] Version release-20191213.0-60-g6410387ff9b4
I0107 06:12:56.301091   31679 x:0] PID: 31679
I0107 06:12:56.301146   31679 x:0] UID: 0, GID: 0
I0107 06:12:56.301188   31679 x:0] Configuration:
I0107 06:12:56.301219   31679 x:0] 		RootDir: /syzkaller/managers/ptrace-direct-overlay-host/workdir/gvisor_root
I0107 06:12:56.301248   31679 x:0] 		Platform: ptrace
I0107 06:12:56.301289   31679 x:0] 		FileAccess: shared, overlay: false
I0107 06:12:56.301352   31679 x:0] 		Network: host, logging: false
I0107 06:12:56.301380   31679 x:0] 		Strace: false, max size: 1024, syscalls: []
I0107 06:12:56.301406   31679 x:0] ***************************
D0107 06:12:56.301502   31679 x:0] Load container "/syzkaller/managers/ptrace-direct-overlay-host/workdir/gvisor_root" "ci-gvisor-ptrace-direct-overlay-host-0"
D0107 06:12:56.303968   31679 x:0] Signal container "ci-gvisor-ptrace-direct-overlay-host-0": signal 0
D0107 06:12:56.304049   31679 x:0] Signal sandbox "ci-gvisor-ptrace-direct-overlay-host-0"
D0107 06:12:56.304090   31679 x:0] Connecting to sandbox "ci-gvisor-ptrace-direct-overlay-host-0"
D0107 06:12:56.304355   31679 x:0] urpc: successfully marshalled 118 bytes.
I0107 06:12:56.633492   31679 x:0] Found sandbox "ci-gvisor-ptrace-direct-overlay-host-0", PID: 58770
I0107 06:12:56.633510   31679 x:0] Retrieving sandbox stacks
D0107 06:12:56.633515   31679 x:0] Stacks sandbox "ci-gvisor-ptrace-direct-overlay-host-0"
D0107 06:12:56.633522   31679 x:0] Connecting to sandbox "ci-gvisor-ptrace-direct-overlay-host-0"
D0107 06:12:56.633579   31679 x:0] urpc: successfully marshalled 36 bytes.
W0107 06:12:56.708137   31679 x:0] FATAL ERROR: retrieving stacks: getting sandbox "ci-gvisor-ptrace-direct-overlay-host-0" stacks: urpc method "debug.Stacks" failed: connection reset by peer
retrieving stacks: getting sandbox "ci-gvisor-ptrace-direct-overlay-host-0" stacks: urpc method "debug.Stacks" failed: connection reset by peer
W0107 06:12:56.708239   31679 x:0] Failure to execute command, err: 1