Program hangs on panic()

[fuyufjh]

What did you do?

Program hanged when I tried to run this: https://play.golang.org/p/TaFytbEfgu

What version of Go are you using (go version)?

go version go1.7.3 darwin/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/yfu/Workspace/Go"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/1g/8s88wqg92kg6lprg5kr2bgmr5x3513/T/go-build297531774=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"

What did you expect to see?

Panic caused by nil pointer, whatever.

What did you see instead?

Program hanged.

[ALTree]

Interesting.. I can reproduce this on 1.7 on Linux, the process is stuck in a loop of some kind, this is a bt:

#0  0x0000000000409438 in runtime.assertE2I2 (inter=0x45b9e0, e=..., r=0xc4218b6328, ~r3=false)
    at /usr/local/go/src/runtime/iface.go:373
#1  0x000000000042252c in runtime.preprintpanics (p=0xc421f2f1b0) at /usr/local/go/src/runtime/panic.go:358
#2  0x000000000042295d in runtime.gopanic (e=...) at /usr/local/go/src/runtime/panic.go:497
#3  0x000000000042157d in runtime.panicmem () at /usr/local/go/src/runtime/panic.go:62
#4  0x0000000000433904 in runtime.sigpanic () at /usr/local/go/src/runtime/sigpanic_unix.go:24
#5  0x0000000000401005 in main.(*MyError).Error (e=0x0, ~r0=...) at /home/adonizetti/Desktop/prova.go:8
#6  0x000000000042254d in runtime.preprintpanics (p=0xc4220ffe40) at /usr/local/go/src/runtime/panic.go:360
#7  0x000000000042295d in runtime.gopanic (e=...) at /usr/local/go/src/runtime/panic.go:497
#8  0x000000000042157d in runtime.panicmem () at /usr/local/go/src/runtime/panic.go:62
#9  0x0000000000433904 in runtime.sigpanic () at /usr/local/go/src/runtime/sigpanic_unix.go:24
#10 0x0000000000401005 in main.(*MyError).Error (e=0x0, ~r0=...) at /home/adonizetti/Desktop/prova.go:8
#11 0x000000000042254d in runtime.preprintpanics (p=0xc4220ffe40) at /usr/local/go/src/runtime/panic.go:360
#12 0x000000000042295d in runtime.gopanic (e=...) at /usr/local/go/src/runtime/panic.go:497
#13 0x000000000042157d in runtime.panicmem () at /usr/local/go/src/runtime/panic.go:62
#14 0x0000000000433904 in runtime.sigpanic () at /usr/local/go/src/runtime/sigpanic_unix.go:24
#15 0x0000000000401005 in main.(*MyError).Error (e=0x0, ~r0=...) at /home/adonizetti/Desktop/prova.go:8
#16 0x000000000042254d in runtime.preprintpanics (p=0xc4220ffe40) at /usr/local/go/src/runtime/panic.go:360
#17 0x000000000042295d in runtime.gopanic (e=...) at /usr/local/go/src/runtime/panic.go:497
#18 0x000000000042157d in runtime.panicmem () at /usr/local/go/src/runtime/panic.go:62
#19 0x0000000000433904 in runtime.sigpanic () at /usr/local/go/src/runtime/sigpanic_unix.go:24
#20 0x0000000000401005 in main.(*MyError).Error (e=0x0, ~r0=...) at /home/adonizetti/Desktop/prova.go:8
#21 0x000000000042254d in runtime.preprintpanics (p=0xc4220ffe40) at /usr/local/go/src/runtime/panic.go:360
#22 0x000000000042295d in runtime.gopanic (e=...) at /usr/local/go/src/runtime/panic.go:497
#23 0x000000000042157d in runtime.panicmem () at /usr/local/go/src/runtime/panic.go:62
#24 0x0000000000433904 in runtime.sigpanic () at /usr/local/go/src/runtime/sigpanic_unix.go:24
#25 0x0000000000401005 in main.(*MyError).Error (e=0x0, ~r0=...) at /home/adonizetti/Desktop/prova.go:8
#26 0x000000000042254d in runtime.preprintpanics (p=0xc4220ffe40) at /usr/local/go/src/runtime/panic.go:360
#27 0x000000000042295d in runtime.gopanic (e=...) at /usr/local/go/src/runtime/panic.go:497
#28 0x000000000042157d in runtime.panicmem () at /usr/local/go/src/runtime/panic.go:62
#29 0x0000000000433904 in runtime.sigpanic () at /usr/local/go/src/runtime/sigpanic_unix.go:24
... and so on ...

It does not hang on tip; it immediately crashes like this:

fatal error: panic while printing panic value
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x44c765]

goroutine 1 [running]:
runtime.throw(0x46a842, 0x20)
    /home/adonizetti/go/src/runtime/panic.go:596 +0x95 fp=0xc42003bce0 sp=0xc42003bcc0
runtime.preprintpanics.func1()
    /home/adonizetti/go/src/runtime/panic.go:385 +0x58 fp=0xc42003bd08 sp=0xc42003bce0
runtime.call32(0x0, 0x46c140, 0x0, 0x0)
    /home/adonizetti/go/src/runtime/asm_amd64.s:501 +0x48 fp=0xc42003bd38 sp=0xc42003bd08
panic(0x45a5c0, 0x499770)
    /home/adonizetti/go/src/runtime/panic.go:489 +0x2d3 fp=0xc42003bdd0 sp=0xc42003bd38
runtime.panicmem()
    /home/adonizetti/go/src/runtime/panic.go:63 +0x5e fp=0xc42003bdf0 sp=0xc42003bdd0
runtime.sigpanic()
    /home/adonizetti/go/src/runtime/signal_unix.go:269 +0x29f fp=0xc42003be40 sp=0xc42003bdf0
main.(*MyError).Error(0x0, 0x459ce0, 0x0)
    /home/adonizetti/Desktop/prova.go:8 +0x5 fp=0xc42003be48 sp=0xc42003be40
runtime.preprintpanics(0xc42003bf30)
    /home/adonizetti/go/src/runtime/panic.go:391 +0xf8 fp=0xc42003bed0 sp=0xc42003be48
panic(0x459ce0, 0x0)
    /home/adonizetti/go/src/runtime/panic.go:528 +0x1ab fp=0xc42003bf68 sp=0xc42003bed0
main.main()
    /home/adonizetti/Desktop/prova.go:16 +0x36 fp=0xc42003bf88 sp=0xc42003bf68
runtime.main()
    /home/adonizetti/go/src/runtime/proc.go:185 +0x20a fp=0xc42003bfe0 sp=0xc42003bf88
runtime.goexit()
    /home/adonizetti/go/src/runtime/asm_amd64.s:2184 +0x1 fp=0xc42003bfe8 sp=0xc42003bfe0

[davecheney]

Ian recently fixed a bug due to a panic during a panic.

This is probably a duplicate.

[0xmohit]

7faf702 would have fixed it.

[ianlancetaylor]

Yes, this should be fixed on tip.