Subject: [PATCH v2 3/3] daemon: explicitly allow EINTR during poll()

From: "Carlo Marcelo Arenas Belón via GitGitGadget" <[email-masked]>
Date: Wed, 25 Jun 2025 07:35:28 +0000

From: =?UTF-8?q?Carlo=20Marcelo=20Arenas=20Bel=C3=B3n?= <[email-masked]>

If the setup for the SIGCHLD signal handler sets SA_RESTART, poll()
might not return with -1 and set errno to EINTR when a signal is
received.

Since the logic to reap zombie childs relies on those interruptions
make sure to explicitly disable SA_RESTART around this function.

Signed-off-by: Carlo Marcelo Arenas Belón <[email-masked]>
---
 daemon.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/daemon.c b/daemon.c
index 8133bd902157..01337fcfedab 100644
--- a/daemon.c
+++ b/daemon.c
@@ -1133,6 +1133,15 @@ static void set_signal_handler(struct sigaction *psa)
 	sigaction(SIGCHLD, psa, NULL);
 }
 
+static void set_sa_restart(struct sigaction *psa, int enable)
+{
+	if (enable)
+		psa->sa_flags |= SA_RESTART;
+	else
+		psa->sa_flags &= ~SA_RESTART;
+	sigaction(SIGCHLD, psa, NULL);
+}
+
 #else
 
 static void set_signal_handler(struct sigaction *psa UNUSED)
@@ -1140,6 +1149,12 @@ static void set_signal_handler(struct sigaction *psa UNUSED)
 	signal(SIGCHLD, child_handler);
 }
 
+static void set_sa_restart(struct sigaction *psa UNUSED, int enable UNUSED)
+{
+}
+
+#endif
+
 static int service_loop(struct socketlist *socklist)
 {
 	struct sigaction sa;
@@ -1157,6 +1172,7 @@ static int service_loop(struct socketlist *socklist)
 	for (;;) {
 		check_dead_children();
 
+		set_sa_restart(&sa, 0);
 		if (poll(pfd, socklist->nr, -1) < 0) {
 			if (errno != EINTR) {
 				logerror("Poll failed, resuming: %s",
@@ -1165,6 +1181,7 @@ static int service_loop(struct socketlist *socklist)
 			}
 			continue;
 		}
+		set_sa_restart(&sa, 1);
 
 		for (size_t i = 0; i < socklist->nr; i++) {
 			if (pfd[i].revents & POLLIN) {
-- 
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