From ae648bafda2d82a6641e4a28bed34dae40d426ec Mon Sep 17 00:00:00 2001
From: Fabricio Voznika <fvoznika@google.com>
Date: Mon, 27 Aug 2018 20:35:00 -0700
Subject: Add command-line parameter to trigger panic on signal

This is to troubleshoot problems with a hung process that is
not responding to 'runsc debug --stack' command.

PiperOrigin-RevId: 210483513
Change-Id: I4377b210b4e51bc8a281ad34fd94f3df13d9187d
---
 runsc/boot/config.go |  6 ++++++
 runsc/boot/loader.go | 14 +++++++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

(limited to 'runsc/boot')

diff --git a/runsc/boot/config.go b/runsc/boot/config.go
index bc392deb3..efb8563ea 100644
--- a/runsc/boot/config.go
+++ b/runsc/boot/config.go
@@ -204,7 +204,12 @@ type Config struct {
 	// TODO: Remove this when multiple container is fully supported.
 	MultiContainer bool
 
+	// WatchdogAction sets what action the watchdog takes when triggered.
 	WatchdogAction watchdog.Action
+
+	// PanicSignal register signal handling that panics. Usually set to
+	// SIGUSR2(12) to troubleshoot hangs. -1 disables it.
+	PanicSignal int
 }
 
 // ToFlags returns a slice of flags that correspond to the given Config.
@@ -225,5 +230,6 @@ func (c *Config) ToFlags() []string {
 		"--strace-syscalls=" + strings.Join(c.StraceSyscalls, ","),
 		"--strace-log-size=" + strconv.Itoa(int(c.StraceLogSize)),
 		"--watchdog-action=" + c.WatchdogAction.String(),
+		"--panic-signal=" + strconv.Itoa(c.PanicSignal),
 	}
 }
diff --git a/runsc/boot/loader.go b/runsc/boot/loader.go
index 3963ed55d..0ad830a6b 100644
--- a/runsc/boot/loader.go
+++ b/runsc/boot/loader.go
@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"math/rand"
 	"os"
+	"os/signal"
 	"runtime"
 	"sync"
 	"sync/atomic"
@@ -229,7 +230,18 @@ func New(spec *specs.Spec, conf *Config, controllerFD int, ioFDs []int, console
 		return nil, fmt.Errorf("failed to ignore child stop signals: %v", err)
 	}
 	// Ensure that signals received are forwarded to the emulated kernel.
-	stopSignalForwarding := sighandling.PrepareForwarding(k, false)()
+	ps := syscall.Signal(conf.PanicSignal)
+	stopSignalForwarding := sighandling.PrepareForwarding(k, ps)()
+	if conf.PanicSignal != -1 {
+		// Panics if the sentry receives 'conf.PanicSignal'.
+		panicChan := make(chan os.Signal, 1)
+		signal.Notify(panicChan, ps)
+		go func() { // S/R-SAFE: causes sentry panic.
+			<-panicChan
+			panic("Signal-induced panic")
+		}()
+		log.Infof("Panic signal set to %v(%d)", ps, conf.PanicSignal)
+	}
 
 	procArgs, err := newProcess(spec, creds, utsns, ipcns, k)
 	if err != nil {
-- 
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