panic: munmap(7fb252800000, 200000)) failed: function not implemented

goroutine 4387 [running]:
gvisor.dev/gvisor/pkg/sentry/platform/ptrace.(*subprocess).Unmap(0xc000138180, 0x7fb252800000, 0x200000)
	pkg/sentry/platform/ptrace/subprocess.go:645 +0x3ff
gvisor.dev/gvisor/pkg/sentry/mm.(*MemoryManager).unmapASLocked(0xc00087f000, 0x7fb252800000, 0x7fb252a00000)
	pkg/sentry/mm/address_space.go:215 +0x73
DIAGNOSIS:
I0919 11:55:22.333253   43133 x:0] ***************************
I0919 11:55:22.333332   43133 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 ci-gvisor-ptrace-direct-overlay-host-1]
I0919 11:55:22.333358   43133 x:0] Version release-20190806.1-158-g28f431335b18
I0919 11:55:22.333363   43133 x:0] PID: 43133
I0919 11:55:22.333370   43133 x:0] UID: 0, GID: 0
I0919 11:55:22.333374   43133 x:0] Configuration:
I0919 11:55:22.333377   43133 x:0] 		RootDir: /syzkaller/managers/ptrace-direct-overlay-host/workdir/gvisor_root
I0919 11:55:22.333455   43133 x:0] 		Platform: ptrace
I0919 11:55:22.333459   43133 x:0] 		FileAccess: shared, overlay: false
I0919 11:55:22.333478   43133 x:0] 		Network: host, logging: false
I0919 11:55:22.333484   43133 x:0] 		Strace: false, max size: 1024, syscalls: []
I0919 11:55:22.333488   43133 x:0] ***************************
D0919 11:55:22.333544   43133 x:0] Load container "/syzkaller/managers/ptrace-direct-overlay-host/workdir/gvisor_root" "ci-gvisor-ptrace-direct-overlay-host-1"
D0919 11:55:22.342039   43133 x:0] Signal container "ci-gvisor-ptrace-direct-overlay-host-1": signal 0
D0919 11:55:22.342072   43133 x:0] Signal sandbox "ci-gvisor-ptrace-direct-overlay-host-1"
D0919 11:55:22.342087   43133 x:0] Connecting to sandbox "ci-gvisor-ptrace-direct-overlay-host-1"
D0919 11:55:22.343850   43133 x:0] urpc: successfully marshalled 118 bytes.
I0919 11:55:22.567238   43133 x:0] Found sandbox "ci-gvisor-ptrace-direct-overlay-host-1", PID: 32600
I0919 11:55:22.567260   43133 x:0] Retrieving sandbox stacks
D0919 11:55:22.567265   43133 x:0] Stacks sandbox "ci-gvisor-ptrace-direct-overlay-host-1"
D0919 11:55:22.567272   43133 x:0] Connecting to sandbox "ci-gvisor-ptrace-direct-overlay-host-1"
D0919 11:55:22.567323   43133 x:0] urpc: successfully marshalled 36 bytes.
W0919 11:55:22.619144   43133 x:0] FATAL ERROR: retrieving stacks: getting sandbox "ci-gvisor-ptrace-direct-overlay-host-1" stacks: urpc method "debug.Stacks" failed: connection reset by peer
retrieving stacks: getting sandbox "ci-gvisor-ptrace-direct-overlay-host-1" stacks: urpc method "debug.Stacks" failed: connection reset by peer
W0919 11:55:22.619240   43133 x:0] Failure to execute command, err: 1