fatal error: unknown caller pc
DIAGNOSIS:
I0229 00:55:07.183700   53515 main.go:305] ***************************
I0229 00:55:07.183751   53515 main.go:306] 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-1]
I0229 00:55:07.183799   53515 main.go:307] Version release-20200219.0-72-gce4d1e45bb88
I0229 00:55:07.183817   53515 main.go:308] PID: 53515
I0229 00:55:07.183836   53515 main.go:309] UID: 0, GID: 0
I0229 00:55:07.183855   53515 main.go:310] Configuration:
I0229 00:55:07.183871   53515 main.go:311] 		RootDir: /syzkaller/managers/ptrace-direct-overlay-host/workdir/gvisor_root
I0229 00:55:07.183924   53515 main.go:312] 		Platform: ptrace
I0229 00:55:07.183956   53515 main.go:313] 		FileAccess: shared, overlay: false
I0229 00:55:07.183981   53515 main.go:314] 		Network: host, logging: false
I0229 00:55:07.184000   53515 main.go:315] 		Strace: false, max size: 1024, syscalls: []
I0229 00:55:07.184030   53515 main.go:316] ***************************
D0229 00:55:07.184075   53515 container.go:159] Load container "/syzkaller/managers/ptrace-direct-overlay-host/workdir/gvisor_root" "ci-gvisor-ptrace-direct-overlay-host-1"
D0229 00:55:07.185349   53515 container.go:592] Signal container "ci-gvisor-ptrace-direct-overlay-host-1": signal 0
D0229 00:55:07.185384   53515 sandbox.go:806] Signal sandbox "ci-gvisor-ptrace-direct-overlay-host-1"
D0229 00:55:07.185399   53515 sandbox.go:318] Connecting to sandbox "ci-gvisor-ptrace-direct-overlay-host-1"
D0229 00:55:07.185556   53515 urpc.go:534] urpc: successfully marshalled 118 bytes.
I0229 00:55:07.443657   53515 debug.go:122] Found sandbox "ci-gvisor-ptrace-direct-overlay-host-1", PID: 45362
I0229 00:55:07.443749   53515 debug.go:131] Retrieving sandbox stacks
D0229 00:55:07.443776   53515 sandbox.go:924] Stacks sandbox "ci-gvisor-ptrace-direct-overlay-host-1"
D0229 00:55:07.443792   53515 sandbox.go:318] Connecting to sandbox "ci-gvisor-ptrace-direct-overlay-host-1"
W0229 00:55:07.443840   53515 error.go:48] FATAL ERROR: retrieving stacks: connecting to control server at PID 45362: connection refused
retrieving stacks: connecting to control server at PID 45362: connection refused
W0229 00:55:07.444073   53515 main.go:338] Failure to execute command, err: 1