[lttng-dev] [PATCH lttng-tools] Fix: ignore SIGPIPE

[Mathieu Desnoyers]

Issuing fprintf() to stderr (thus write() to the standard error file
descriptor) within the SIGPIPE signal handler is bad: it can trigger
SIGPIPE repeatedly if the listening end has closed its end of the pipe.

Set the SIGPIPE action to SIG_IGN in relayd, sessiond, and consumerd.

This was affecting sessiond and relayd. The consumerd did not print
anything to stderr.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
---
 src/bin/lttng-consumerd/lttng-consumerd.c | 12 +++---------
 src/bin/lttng-relayd/main.c               | 11 +++++------
 src/bin/lttng-sessiond/main.c             | 11 +++++------
 3 files changed, 13 insertions(+), 21 deletions(-)

diff --git a/src/bin/lttng-consumerd/lttng-consumerd.c b/src/bin/lttng-consumerd/lttng-consumerd.c
index 1636b9c..1373a74 100644
--- a/src/bin/lttng-consumerd/lttng-consumerd.c
+++ b/src/bin/lttng-consumerd/lttng-consumerd.c
@@ -99,14 +99,6 @@ static void sighandler(int sig)
 		return;
 	}
 
-	/*
-	 * Ignore SIGPIPE because it should not stop the consumer whenever a
-	 * SIGPIPE is caught through a FD operation.
-	 */
-	if (sig == SIGPIPE) {
-		return;
-	}
-
 	if (ctx) {
 		lttng_consumer_should_exit(ctx);
 	}
@@ -127,9 +119,10 @@ static int set_signal_handler(void)
 		return ret;
 	}
 
-	sa.sa_handler = sighandler;
 	sa.sa_mask = sigset;
 	sa.sa_flags = 0;
+
+	sa.sa_handler = sighandler;
 	if ((ret = sigaction(SIGTERM, &sa, NULL)) < 0) {
 		PERROR("sigaction");
 		return ret;
@@ -140,6 +133,7 @@ static int set_signal_handler(void)
 		return ret;
 	}
 
+	sa.sa_handler = SIG_IGN;
 	if ((ret = sigaction(SIGPIPE, &sa, NULL)) < 0) {
 		PERROR("sigaction");
 		return ret;
diff --git a/src/bin/lttng-relayd/main.c b/src/bin/lttng-relayd/main.c
index e8f3087..ea46ec7 100644
--- a/src/bin/lttng-relayd/main.c
+++ b/src/bin/lttng-relayd/main.c
@@ -582,9 +582,6 @@ int lttng_relay_stop_threads(void)
 static void sighandler(int sig)
 {
 	switch (sig) {
-	case SIGPIPE:
-		DBG("SIGPIPE caught");
-		return;
 	case SIGINT:
 		DBG("SIGINT caught");
 		if (lttng_relay_stop_threads()) {
@@ -620,9 +617,10 @@ static int set_signal_handler(void)
 		return ret;
 	}
 
-	sa.sa_handler = sighandler;
 	sa.sa_mask = sigset;
 	sa.sa_flags = 0;
+
+	sa.sa_handler = sighandler;
 	if ((ret = sigaction(SIGTERM, &sa, NULL)) < 0) {
 		PERROR("sigaction");
 		return ret;
@@ -633,12 +631,13 @@ static int set_signal_handler(void)
 		return ret;
 	}
 
-	if ((ret = sigaction(SIGPIPE, &sa, NULL)) < 0) {
+	if ((ret = sigaction(SIGUSR1, &sa, NULL)) < 0) {
 		PERROR("sigaction");
 		return ret;
 	}
 
-	if ((ret = sigaction(SIGUSR1, &sa, NULL)) < 0) {
+	sa.sa_handler = SIG_IGN;
+	if ((ret = sigaction(SIGPIPE, &sa, NULL)) < 0) {
 		PERROR("sigaction");
 		return ret;
 	}
diff --git a/src/bin/lttng-sessiond/main.c b/src/bin/lttng-sessiond/main.c
index 1964fe0..a2afb8f 100644
--- a/src/bin/lttng-sessiond/main.c
+++ b/src/bin/lttng-sessiond/main.c
@@ -5370,9 +5370,6 @@ error:
 static void sighandler(int sig)
 {
 	switch (sig) {
-	case SIGPIPE:
-		DBG("SIGPIPE caught");
-		return;
 	case SIGINT:
 		DBG("SIGINT caught");
 		stop_threads();
@@ -5404,9 +5401,10 @@ static int set_signal_handler(void)
 		return ret;
 	}
 
-	sa.sa_handler = sighandler;
 	sa.sa_mask = sigset;
 	sa.sa_flags = 0;
+
+	sa.sa_handler = sighandler;
 	if ((ret = sigaction(SIGTERM, &sa, NULL)) < 0) {
 		PERROR("sigaction");
 		return ret;
@@ -5417,12 +5415,13 @@ static int set_signal_handler(void)
 		return ret;
 	}
 
-	if ((ret = sigaction(SIGPIPE, &sa, NULL)) < 0) {
+	if ((ret = sigaction(SIGUSR1, &sa, NULL)) < 0) {
 		PERROR("sigaction");
 		return ret;
 	}
 
-	if ((ret = sigaction(SIGUSR1, &sa, NULL)) < 0) {
+	sa.sa_handler = SIG_IGN;
+	if ((ret = sigaction(SIGPIPE, &sa, NULL)) < 0) {
 		PERROR("sigaction");
 		return ret;
 	}
-- 
2.1.4