[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 <nam...@linutronix.de>
---
 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