panic: munmap(a00000, 200000)) failed: function not implemented

goroutine 231 [running]:
gvisor.dev/gvisor/pkg/sentry/platform/ptrace.(*subprocess).Unmap(0xc00034c0c0, 0xa00000, 0x200000)
	pkg/sentry/platform/ptrace/subprocess.go:658 +0x3ff
gvisor.dev/gvisor/pkg/sentry/mm.(*MemoryManager).unmapASLocked(0xc0009f0000, 0xa00000, 0xc00000)
	pkg/sentry/mm/address_space.go:215 +0x73
gvisor.dev/gvisor/pkg/sentry/mm.(*MemoryManager).getPMAsInternalLocked(0xc0009f0000, 0xee77e0, 0xc000a08000, 0xc0009f0080, 0x4, 0xa67000, 0xa68000, 0x101, 0xee2a40, 0xc0010a3d40, ...)
	pkg/sentry/mm/pma.go:357 +0x12a8
gvisor.dev/gvisor/pkg/sentry/mm.(*MemoryManager).getPMAsLocked(0xc0009f0000, 0xee77e0, 0xc000a08000, 0xc0009f0080, 0x4, 0xa67000, 0xa68000, 0x101, 0xc0009f0080, 0x5, ...)
DIAGNOSIS:
I1210 13:41:24.916816   15454 x:0] ***************************
I1210 13:41:24.916834   15454 x:0] Args: [/syzkaller/managers/main/current/image -root /syzkaller/managers/main/workdir/gvisor_root -watchdog-action=panic -network=none -debug -alsologtostderr -platform=ptrace -file-access=shared -network=none debug -stacks ci-gvisor-main-2]
I1210 13:41:24.916859   15454 x:0] Version release-20191129.0-30-g98aafb1334b8
I1210 13:41:24.916872   15454 x:0] PID: 15454
I1210 13:41:24.916879   15454 x:0] UID: 0, GID: 0
I1210 13:41:24.916883   15454 x:0] Configuration:
I1210 13:41:24.916892   15454 x:0] 		RootDir: /syzkaller/managers/main/workdir/gvisor_root
I1210 13:41:24.916896   15454 x:0] 		Platform: ptrace
I1210 13:41:24.916899   15454 x:0] 		FileAccess: shared, overlay: false
I1210 13:41:24.916915   15454 x:0] 		Network: none, logging: false
I1210 13:41:24.916922   15454 x:0] 		Strace: false, max size: 1024, syscalls: []
I1210 13:41:24.916927   15454 x:0] ***************************
D1210 13:41:24.916959   15454 x:0] Load container "/syzkaller/managers/main/workdir/gvisor_root" "ci-gvisor-main-2"
D1210 13:41:24.918894   15454 x:0] Signal container "ci-gvisor-main-2": signal 0
D1210 13:41:24.918917   15454 x:0] Signal sandbox "ci-gvisor-main-2"
D1210 13:41:24.918923   15454 x:0] Connecting to sandbox "ci-gvisor-main-2"
D1210 13:41:24.919069   15454 x:0] urpc: successfully marshalled 96 bytes.
I1210 13:41:25.282471   15454 x:0] Found sandbox "ci-gvisor-main-2", PID: 21976
I1210 13:41:25.282485   15454 x:0] Retrieving sandbox stacks
D1210 13:41:25.282490   15454 x:0] Stacks sandbox "ci-gvisor-main-2"
D1210 13:41:25.282501   15454 x:0] Connecting to sandbox "ci-gvisor-main-2"
D1210 13:41:25.282545   15454 x:0] urpc: successfully marshalled 36 bytes.
W1210 13:41:25.344498   15454 x:0] FATAL ERROR: retrieving stacks: getting sandbox "ci-gvisor-main-2" stacks: urpc method "debug.Stacks" failed: connection reset by peer
retrieving stacks: getting sandbox "ci-gvisor-main-2" stacks: urpc method "debug.Stacks" failed: connection reset by peer
W1210 13:41:25.344602   15454 x:0] Failure to execute command, err: 1