Subject: [PATCH v3 4/4] daemon: explicitly allow EINTR during poll()

From: "Carlo Marcelo Arenas Belón via GitGitGadget" <[email-masked]>
Date: Thu, 26 Jun 2025 08:53:08 +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 | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/daemon.c b/daemon.c
index 155b2e180167..7e29c03e313f 100644
--- a/daemon.c
+++ b/daemon.c
@@ -1116,6 +1116,25 @@ static void socksetup(struct string_list *listen_addr, int listen_port, struct s
 	}
 }
 
+#ifndef NO_RESTARTABLE_SIGNALS
+
+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_sa_restart(struct sigaction *psa UNUSED, int enable UNUSED)
+{
+}
+
+#endif
+
 static int service_loop(struct socketlist *socklist)
 {
 	struct sigaction sa;
@@ -1136,6 +1155,7 @@ 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",
@@ -1144,6 +1164,7 @@ 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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