[PATCH] selftests/cgroup: Decode waitid results correctly in clone_reap

[PATCH] selftests/cgroup: Decode waitid results correctly in clone_reap

[Kanishk Singh]

clone_reap() applies the waitpid() status macros to waitid()'s
si_status. Unlike waitpid()'s encoded status, si_status already holds
the exit code or signal number, and si_code identifies the event.

For example, a child exiting with status 128 is reported as successful,
while a child exiting with status 42 produces -1 rather than 42. Stop
and continuation events are also rejected. With WNOHANG, a live child
can be reported as having exited successfully because the zeroed
si_status passes WIFEXITED().

Check si_code for the requested event and return si_status directly
for exit and stop events. Accept CLD_TRAPPED along with CLD_STOPPED,
as both correspond to stopped children.

Fixes: 27eaaaf3b30e ("selftests/cgroup: add tests for cloning into cgroups")
Signed-off-by: Kanishk Singh <kanishk2607@gmail.com>
---
This patch was prepared with ChatGPT/Codex assistance for code inspection,
implementation, commit-message drafting, and local testing. The task was to
find and reproduce a cgroup selftest helper bug, make a focused fix, and
verify the result against the original helper.

Testing: the cgroup selftest programs build successfully. A standalone
reproducer linked against cgroup_util.c passes all 256 exit codes, SIGSTOP,
SIGCONT, SIGKILL, WNOHANG, ECHILD, and an interrupted wait after this change.
The original helper fails 255 of the 256 exit-code comparisons, the stop
and continuation checks, the WNOHANG check, and the interrupted-wait
exit-code check. No full cgroup runtime suite was run: the environment has
no cgroup mount. A ptrace stop check was skipped because PTRACE_TRACEME
was unavailable.

 tools/testing/selftests/cgroup/lib/cgroup_util.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/cgroup/lib/cgroup_util.c
b/tools/testing/selftests/cgroup/lib/cgroup_util.c
index 823b0312b..4915d80ed 100644
--- a/tools/testing/selftests/cgroup/lib/cgroup_util.c
+++ b/tools/testing/selftests/cgroup/lib/cgroup_util.c
@@ -508,17 +508,17 @@ int clone_reap(pid_t pid, int options)
 	}

 	if (options & WEXITED) {
-		if (WIFEXITED(info.si_status))
-			return WEXITSTATUS(info.si_status);
+		if (info.si_code == CLD_EXITED)
+			return info.si_status;
 	}

 	if (options & WSTOPPED) {
-		if (WIFSTOPPED(info.si_status))
-			return WSTOPSIG(info.si_status);
+		if (info.si_code == CLD_STOPPED || info.si_code == CLD_TRAPPED)
+			return info.si_status;
 	}

 	if (options & WCONTINUED) {
-		if (WIFCONTINUED(info.si_status))
+		if (info.si_code == CLD_CONTINUED)
 			return 0;
 	}


base-commit: 067c5c24cef23d913b67eaaf71ae67e7169a6620
-- 
2.52.0

Re: [PATCH] selftests/cgroup: Decode waitid results correctly in clone_reap

[Tejun Heo]

Applied to cgroup/for-7.5 with the Fixes tag dropped.

Thanks.

--
tejun