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/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
index 7b353c8553a0352a85ab4a95c2944752a691cbae..716795e0e818028d1a6fc6fa63374abaaf0ebafa 100644 (file)
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -1293,14 +1293,14 @@ 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;
                }