runtime: fatal error: stack growth after fork

[honsunrise]

go/src/runtime/runtime2.go

Lines 211 to 215 in 2feb2cc

	func efaceOf(ep *interface{}) *eface {
	return (*eface)(unsafe.Pointer(ep))
	}

Why this func not have //go:nosplit?

go/src/runtime/proc.go

Lines 446 to 449 in c580180

	//go:nosplit
	func funcPC(f interface{}) uintptr {
	return *(*uintptr)(efaceOf(&f).data)
	}

When setsig call funcPC, there will be panic!

fatal error: stack growth after fork

runtime stack:
runtime.throw(0x8afa736, 0x17)
	/usr/local/go/src/runtime/panic.go:1117 +0x6a
runtime.newstack()
	/usr/local/go/src/runtime/stack.go:942 +0xc58
runtime.morestack()
	/usr/local/go/src/runtime/asm_386.s:471 +0x7f

goroutine 50 [running, locked to thread]:
runtime.efaceOf(0xaa23554, 0xa51c72c0)
	/usr/local/go/src/runtime/runtime2.go:213 +0x20 fp=0xaa23548 sp=0xaa23544 pc=0x8091a20
runtime.funcPC(0x89fea00, 0x8b2e9dc, 0x0)
	/usr/local/go/src/runtime/proc.go:448 +0xf fp=0xaa23554 sp=0xaa23548 pc=0x808322f
runtime.setsig(0x1, 0x0)
	/usr/local/go/src/runtime/os_linux.go:427 +0x3a fp=0xaa23578 sp=0xaa23554 pc=0x807d13a
runtime.clearSignalHandlers()
	/usr/local/go/src/runtime/signal_unix.go:259 +0x44 fp=0xaa23588 sp=0xaa23578 pc=0x80950d4
syscall.runtime_AfterForkInChild()
	/usr/local/go/src/runtime/proc.go:3951 +0xf fp=0xaa2359c sp=0xaa23588 pc=0x80ae48f
syscall.forkAndExecInChild1(0xaa26730, 0xaa10168, 0x5, 0x5, 0xaa341c0, 0x1a, 0x1a, 0x0, 0x0, 0xaa23a28, ...)
	/usr/local/go/src/syscall/exec_linux.go:240 +0x6e0 fp=0xaa23794 sp=0xaa2359c pc=0x80c0640
syscall.forkAndExecInChild(0xaa26730, 0xaa10168, 0x5, 0x5, 0xaa341c0, 0x1a, 0x1a, 0x0, 0x0, 0xaa23a28, ...)
	/usr/local/go/src/syscall/exec_linux.go:83 +0xf8 fp=0xaa23830 sp=0xaa23794 pc=0x80bfcd8
syscall.forkExec(0xa89e190, 0x45, 0xaa4a1c0, 0x4, 0x4, 0xaa23a28, 0x0, 0x0, 0x0)
	/usr/local/go/src/syscall/exec_unix.go:211 +0x791 fp=0xaa23930 sp=0xaa23830 pc=0x80c3ad1
syscall.StartProcess(0xa89e190, 0x45, 0xaa4a1c0, 0x4, 0x4, 0xaa23a28, 0x0, 0x0, 0x0, 0x0)
	/usr/local/go/src/syscall/exec_unix.go:263 +0x7d fp=0xaa23964 sp=0xaa23930 pc=0x80c3efd
os.startProcess(0xa89e190, 0x45, 0xaa4a1c0, 0x4, 0x4, 0xaa28600, 0x0, 0x0, 0x0)
	/usr/local/go/src/os/exec_posix.go:53 +0x432 fp=0xaa23a50 sp=0xaa23964 pc=0x815ad42
os.StartProcess(0xa89e190, 0x45, 0xaa4a1c0, 0x4, 0x4, 0xaa28600, 0x0, 0x0, 0x0)
	/usr/local/go/src/os/exec.go:106 +0x91 fp=0xaa23a90 sp=0xaa23a50 pc=0x815a4d1
...
...

[gopherbot]

Change https://golang.org/cl/356109 mentions this issue: runtime: add missing //go:nosplit for efaceOf

[mknyszek]

What version of Go are you using? setsig doesn't seem to call through funcPC at present (replaced with the new intrinsics in 1.17: https://cs.opensource.google/go/go/+/master:src/runtime/os_linux.go;l=445;drc=master;bpv=1;bpt=1).

We should maybe backport this though? A stack growth during a vfork or something sounds pretty bad.

[honsunrise]

I'm using go1.17.2 and have also tested it on 1.16.9.

Yes we should be backport this, the master branch does not need this patch.