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 <[email protected]>
Link: https://lore.kernel.org/ee657f3fc8e19657cf7aaa366552d6347728f371.1744383419.git.namcao@linutronix.de
Signed-off-by: Christian Brauner <[email protected]>

Author: covanam

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)