From ae65491223a460b0a902993ac81ac91ca69c91fa Mon Sep 17 00:00:00 2001
From: Ophestra <cat@gensokyo.uk>
Date: Wed, 15 Oct 2025 21:35:19 +0900
Subject: [PATCH] container/init: use one channel for wait4

When using two channels it is possible for the other case to be reached before all pending winfo are consumed, causing incorrect reporting.

Signed-off-by: Ophestra <cat@gensokyo.uk>
---
 container/init.go      | 20 +++++++++++++-------
 container/init_test.go | 12 ++++++++++++
 2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/container/init.go b/container/init.go
index ff72c40..e38127f 100644
--- a/container/init.go
+++ b/container/init.go
@@ -353,10 +353,14 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 		wpid    int
 		wstatus WaitStatus
 	}
+
+	// info is closed as the wait4 thread terminates
+	// when there are no longer any processes left to reap
 	info := make(chan winfo, 1)
-	done := make(chan struct{})
 
 	k.new(func(k syscallDispatcher) {
+		k.lockOSThread()
+
 		var (
 			err     error
 			wpid    = -2
@@ -382,7 +386,7 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 			k.printf(msg, "unexpected wait4 response: %v", err)
 		}
 
-		close(done)
+		close(info)
 	})
 
 	// handle signals to dump withheld messages
@@ -411,7 +415,13 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 			msg.BeforeExit()
 			k.exit(0)
 
-		case w := <-info:
+		case w, ok := <-info:
+			if !ok {
+				msg.BeforeExit()
+				k.exit(r)
+				continue // unreachable
+			}
+
 			if w.wpid == cmd.Process.Pid {
 				// initial process exited, output is most likely available again
 				msg.Resume()
@@ -433,10 +443,6 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 				go func() { time.Sleep(params.AdoptWaitDelay); close(timeout) }()
 			}
 
-		case <-done:
-			msg.BeforeExit()
-			k.exit(r)
-
 		case <-timeout:
 			k.printf(msg, "timeout exceeded waiting for lingering processes")
 			msg.BeforeExit()
diff --git a/container/init_test.go b/container/init_test.go
index 4973972..c3f2197 100644
--- a/container/init_test.go
+++ b/container/init_test.go
@@ -2081,6 +2081,8 @@ func TestInitEntrypoint(t *testing.T) {
 
 			/* wait4 */
 			Tracks: []stub.Expect{{Calls: []stub.Call{
+				call("lockOSThread", stub.ExpectArgs{}, nil, nil),
+
 				// magicWait4Signal as args[4] causes this to block until simulated signal is delivered
 				call("wait4", stub.ExpectArgs{-1, syscall.WaitStatus(0xfade01ce), 0, nil, magicWait4Signal}, 0xbad, nil),
 				// this terminates the goroutine at the call, preventing it from leaking while preserving behaviour
@@ -2174,6 +2176,8 @@ func TestInitEntrypoint(t *testing.T) {
 
 			/* wait4 */
 			Tracks: []stub.Expect{{Calls: []stub.Call{
+				call("lockOSThread", stub.ExpectArgs{}, nil, nil),
+
 				// this terminates the goroutine at the call, preventing it from leaking while preserving behaviour
 				call("wait4", stub.ExpectArgs{-1, nil, 0, nil, stub.PanicExit}, 0, syscall.ECHILD),
 			}}},
@@ -2266,6 +2270,8 @@ func TestInitEntrypoint(t *testing.T) {
 
 			/* wait4 */
 			Tracks: []stub.Expect{{Calls: []stub.Call{
+				call("lockOSThread", stub.ExpectArgs{}, nil, nil),
+
 				call("wait4", stub.ExpectArgs{-1, syscall.WaitStatus(0xfade01ce), 0, nil}, 0xbad, nil),
 				// this terminates the goroutine at the call, preventing it from leaking while preserving behaviour
 				call("wait4", stub.ExpectArgs{-1, nil, 0, nil, 0xdeadbeef}, 0, syscall.ECHILD),
@@ -2358,6 +2364,8 @@ func TestInitEntrypoint(t *testing.T) {
 
 			/* wait4 */
 			Tracks: []stub.Expect{{Calls: []stub.Call{
+				call("lockOSThread", stub.ExpectArgs{}, nil, nil),
+
 				call("wait4", stub.ExpectArgs{-1, nil, 0, nil}, 0, syscall.EINTR),
 				call("wait4", stub.ExpectArgs{-1, nil, 0, nil}, 0, syscall.EINTR),
 				call("wait4", stub.ExpectArgs{-1, syscall.WaitStatus(0xdeaf), 0, nil}, 0xbabe, nil),
@@ -2494,6 +2502,8 @@ func TestInitEntrypoint(t *testing.T) {
 
 			/* wait4 */
 			Tracks: []stub.Expect{{Calls: []stub.Call{
+				call("lockOSThread", stub.ExpectArgs{}, nil, nil),
+
 				call("wait4", stub.ExpectArgs{-1, nil, 0, nil}, 0, syscall.EINTR),
 				call("wait4", stub.ExpectArgs{-1, nil, 0, nil}, 0, syscall.EINTR),
 				call("wait4", stub.ExpectArgs{-1, syscall.WaitStatus(0xdeaf), 0, nil}, 0xbabe, nil),
@@ -2634,6 +2644,8 @@ func TestInitEntrypoint(t *testing.T) {
 
 			/* wait4 */
 			Tracks: []stub.Expect{{Calls: []stub.Call{
+				call("lockOSThread", stub.ExpectArgs{}, nil, nil),
+
 				call("wait4", stub.ExpectArgs{-1, nil, 0, nil}, 0, syscall.EINTR),
 				call("wait4", stub.ExpectArgs{-1, nil, 0, nil}, 0, syscall.EINTR),
 				call("wait4", stub.ExpectArgs{-1, syscall.WaitStatus(0xdeaf), 0, nil}, 0xbabe, nil),