selftests: coredump: Fix test failure for slow machines

JIRA: https://issues.redhat.com/browse/RHEL-113598

commit 6f5bf9f
Author: Nam Cao <namcao@linutronix.de>
Date:   Fri, 11 Apr 2025 17:09:42 +0200

    selftests: coredump: Fix test failure for slow machines

    The test waits for coredump to finish by busy-waiting for the stack_values
    file to be created. The maximum wait time is 10 seconds.

    This doesn't work for slow machine (qemu-system-riscv64), because coredump
    takes longer.

    Fix it by waiting for the crashing child process to finish first.

    Fixes: 15858da ("selftests: coredump: Add stackdump test")
    Signed-off-by: Nam Cao <namcao@linutronix.de>
    Link: https://lore.kernel.org/ee657f3fc8e19657cf7aaa366552d6347728f371.1744383419.git.namcao@linutronix.de
    Signed-off-by: Christian Brauner <brauner@kernel.org>

Signed-off-by: Waiman Long <longman@redhat.com>

Author: Waiman-Long

tools/testing/selftests/coredump/stackdump_test.c

@@ -96,7 +96,7 @@ TEST_F(coredump, stackdump)
 	char *test_dir, *line;
 	size_t line_length;
 	char buf[PATH_MAX];
-	int ret, i;
+	int ret, i, status;
 	FILE *file;
 	pid_t pid;
 
@@ -129,6 +129,10 @@ TEST_F(coredump, stackdump)
 	/*
 	 * Step 3: Wait for the stackdump script to write the stack pointers to the stackdump file
 	 */
+	waitpid(pid, &status, 0);
+	ASSERT_TRUE(WIFSIGNALED(status));
+	ASSERT_TRUE(WCOREDUMP(status));
+
 	for (i = 0; i < 10; ++i) {
 		file = fopen(STACKDUMP_FILE, "r");
 		if (file)