fatal error: unknown caller pc

runtime stack:
runtime.throw({0x11d0713?, 0x1d50ae0?})
	GOROOT/src/runtime/panic.go:992 +0x71 fp=0xc000d25bf0 sp=0xc000d25bc0 pc=0x435c91
runtime.gentraceback(0xc000102d00?, 0xc000d25f80?, 0xc000b0aea0?, 0xc0008fd380?, 0x0, 0x0, 0x7fffffff, 0xc000d25fa0, 0x400000002?, 0x0)
	GOROOT/src/runtime/traceback.go:254 +0x1a36 fp=0xc000d25f50 sp=0xc000d25bf0 pc=0x45c4b6
runtime.addOneOpenDeferFrame.func1()
	GOROOT/src/runtime/panic.go:599 +0x6b fp=0xc000d25fc8 sp=0xc000d25f50 pc=0x434e4b
runtime.systemstack()
	src/runtime/asm_amd64.s:469 +0x49 fp=0xc000d25fd0 sp=0xc000d25fc8 pc=0x4672a9