Ignore SIGURG signals in signal forwarder

cpuguy83 · cpuguy83 · commit 899b4e3cb55b · 2020-09-04T16:19:31.000-07:00
Starting with go1.14, the go runtime hijacks SIGURG but with no way to
not send to other signal handlers.

In practice, we get this signal frequently.
I found this while testing out go1.15 with ctr and multiple execs with
only `echo hello`. When the process exits quickly, if the previous
commit is not applied, you end up with an error message that it couldn't
forward SIGURG to the container (due to the process being gone).

Signed-off-by: Brian Goff &lt;cpuguy83@gmail.com&gt;
diff --git a/cmd/ctr/commands/signals.go b/cmd/ctr/commands/signals.go
@@ -37,6 +37,10 @@ func ForwardAllSignals(ctx gocontext.Context, task killer) chan os.Signal {
 	signal.Notify(sigc)
 	go func() {
 		for s := range sigc {
+			if canIgnoreSignal(s) {
+				logrus.Debugf("Ignoring signal %s", s)
+				continue
+			}
 			logrus.Debug("forwarding signal ", s)
 			if err := task.Kill(ctx, s.(syscall.Signal)); err != nil {
 				if errdefs.IsNotFound(err) {
diff --git a/cmd/ctr/commands/signals_linux.go b/cmd/ctr/commands/signals_linux.go
@@ -0,0 +1,27 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package commands
+
+import (
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+func canIgnoreSignal(s os.Signal) bool {
+	return s == unix.SIGURG
+}
diff --git a/cmd/ctr/commands/signals_notlinux.go b/cmd/ctr/commands/signals_notlinux.go
@@ -0,0 +1,25 @@
+//+build !linux
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package commands
+
+import "os"
+
+func canIgnoreSignal(_ os.Signal) bool {
+	return false
+}
