runtime: crash in GoroutineProfile

[rsc]

This program should run forever. It crashes quickly, because GoroutineProfile is using
the wrong pc/sp combination for the traceback if the corresponding goroutine has just
come out of a system call.

The only workaround is not to call GoroutineProfile. Possible #go121 candidate.

package main

import (
    "runtime"
    "syscall"
)

func main() {
    runtime.GOMAXPROCS(200)
    for i := 0; i < 10; i++ {
        go func() {
            for {
                syscall.Close(-1)
            }
        }()
    }
    stk := make([]runtime.StackRecord, 1000)
    for n := 0;; n++ {
        _, ok := runtime.GoroutineProfile(stk)
        if !ok {
            panic("GoroutineProfile refused")
        }
        if n&(n-1) == 0 {
            println(n)
        }
    }
}

panic: invalid memory address or nil pointer dereference
fatal error: panic during gc
[signal 0xb code=0x1 addr=0x0 pc=0x1a7f5]

goroutine 1 [running]:
runtime.throw(0x6b1ac)
    /Users/rsc/g/go/src/pkg/runtime/panic.c:462 +0x69 fp=0x2210248d40
runtime.panicstring(0x6b5b9)
    /Users/rsc/g/go/src/pkg/runtime/panic.c:477 +0x8d fp=0x2210248d68
runtime.sigpanic()
    /Users/rsc/g/go/src/pkg/runtime/os_darwin.c:450 +0x16a fp=0x2210248d80
runtime.gentraceback(0x7850, 0x0, 0x0, 0x2100d8ea0, 0x0, ...)
    /Users/rsc/g/go/src/pkg/runtime/traceback_x86.c:101 +0x745 fp=0x2210248e40
saveg(0x7850, 0x0, 0x2100d8ea0, 0x210148600)
    /Users/rsc/rscgo/src/pkg/runtime/mprof.goc:531 +0x76 fp=0x2210248ea0
runtime.GoroutineProfile(0x210148000, 0x3e8, 0x3e8, 0xc, 0x301)
    /Users/rsc/rscgo/src/pkg/runtime/mprof.goc:559 +0x148 fp=0x2210248ee8
main.main()
    /Users/rsc/x.go:19 +0xbd fp=0x2210248f48
runtime.main()
    /Users/rsc/g/go/src/pkg/runtime/proc.c:220 +0x11f fp=0x2210248fa0
runtime.goexit()
    /Users/rsc/g/go/src/pkg/runtime/proc.c:1394 fp=0x2210248fa8

[rsc]

Comment 1:

https://golang.org/cl/41640043

[ianlancetaylor]

Comment 2:

This meets the criteria for 1.2.x release: a critical bug with no workaround.  The
#go121 tag in the text isn't sufficient, because we not only need a way to mark issues
as appropriate for 1.2.1, but we also need a way to remove that marking.  So I'm
changing the release tag to Release-Go1.2.1.

Labels changed: added release-go1.2.1, removed release-go1.3.

[rsc]

Comment 3:

This issue was closed by revision bc135f6.

Status changed to Fixed.

[rsc]

Comment 4:

Okay for 1.2.1.

[rsc]

Comment 5:

This issue was closed by revision 7ada9e760ce3.