From: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Date: Wed, 14 Sep 2022 12:37:35 +0000 (+0100)
Subject: Fix: lttng-ust-comm: wait on wrong child process
X-Git-Url: http://git.liburcu.org/?p=lttng-ust.git;a=commitdiff_plain;h=f8efdde9fd8fa32c4313c2848cc6bcb42a3d5871

Fix: lttng-ust-comm: wait on wrong child process

The code currently assumes that the forked process is the only child
process at that point in time. However, there can be unreaped child
processes as reported in the original bug.

From wait(3), as currently used, "status is requested for any child
process."

Using the pid explicitly ensures a wait on the expected child process.

More context is available at:
https://bugs.lttng.org/issues/1359

Fixes #1359
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I8a4621d79c61f7dfefde5c2b94bdee9752e1973d
---

diff --git a/src/lib/lttng-ust/lttng-ust-comm.c b/src/lib/lttng-ust/lttng-ust-comm.c
index 0fe2da46..7903550f 100644
--- a/src/lib/lttng-ust/lttng-ust-comm.c
+++ b/src/lib/lttng-ust/lttng-ust-comm.c
@@ -1584,14 +1584,14 @@ open_write:
 	pid = fork();
 	URCU_TLS(lttng_ust_nest_count)--;
 	if (pid > 0) {
-		int status;
+		int status, wait_ret;
 
 		/*
 		 * Parent: wait for child to return, in which case the
 		 * shared memory map will have been created.
 		 */
-		pid = wait(&status);
-		if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+		wait_ret = waitpid(pid, &status, 0);
+		if (wait_ret < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 			wait_shm_fd = -1;
 			goto end;
 		}