[PATCH 2/3] selftests: coredump: Use waitpid() instead of busy-wait

[Nam Cao]

The test waits for coredump to finish by busy-waiting for the
stackdump_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.

Switch to use waitpid().

With this, the stack_values file doesn't need to be atomically written by
coredump anymore, therefore simplify the stackdump script.

Fixes: 15858da53542 ("selftests: coredump: Add stackdump test")
Signed-off-by: Nam Cao <namcao@xxxxxxxxxxxxx>
---
 tools/testing/selftests/coredump/stackdump        |  6 +-----
 tools/testing/selftests/coredump/stackdump_test.c | 13 ++++++-------
 2 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/tools/testing/selftests/coredump/stackdump b/tools/testing/selftests/coredump/stackdump
index 96714ce42d12..ad487fd5ff15 100755
--- a/tools/testing/selftests/coredump/stackdump
+++ b/tools/testing/selftests/coredump/stackdump
@@ -4,11 +4,7 @@
 CRASH_PROGRAM_ID=$1
 STACKDUMP_FILE=$2
 
-TMP=$(mktemp)
-
 for t in /proc/$CRASH_PROGRAM_ID/task/*; do
 	tid=$(basename $t)
-	cat /proc/$tid/stat | awk '{print $29}' >> $TMP
+	cat /proc/$tid/stat | awk '{print $29}' >> $STACKDUMP_FILE
 done
-
-mv $TMP $STACKDUMP_FILE
diff --git a/tools/testing/selftests/coredump/stackdump_test.c b/tools/testing/selftests/coredump/stackdump_test.c
index 1dc54e128586..733feaa0f895 100644
--- a/tools/testing/selftests/coredump/stackdump_test.c
+++ b/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;
 
@@ -131,12 +131,11 @@ TEST_F(coredump, stackdump)
 	/*
 	 * Step 3: Wait for the stackdump script to write the stack pointers to the stackdump file
 	 */
-	for (i = 0; i < 10; ++i) {
-		file = fopen(STACKDUMP_FILE, "r");
-		if (file)
-			break;
-		sleep(1);
-	}
+	waitpid(pid, &status, 0);
+	ASSERT_TRUE(WIFSIGNALED(status));
+	ASSERT_TRUE(WCOREDUMP(status));
+
+	file = fopen(STACKDUMP_FILE, "r");
 	ASSERT_NE(file, NULL);
 
 	/* Step 4: Make sure all stack pointer values are non-zero */
-- 
2.39.5