[LTP] thp04: Add ptrace mode and fix tracee stop synchronization

[linuxtestproject.agent@gmail.com]

Hi Jan,

On Thu Jul 9 2026, Jan Polensky wrote:
> thp04: Add ptrace mode and fix tracee stop synchronization

The subject says "fix tracee stop synchronization". The original test
had no tracee or ptrace code at all -- this is entirely new logic.
"fix" suggests something broken was corrected. "add" would be more
accurate here.

> +static void tracee_main(void)
> +{
> ...
> +	/*
> +	 * Run indefinitely - parent controls termination via PTRACE_DETACH.
> +	 */

The actual termination sequence in run_proc_mem_ptrace_serialized() is
PTRACE_DETACH followed by SIGKILL. PTRACE_DETACH alone does not stop
the tracee; the parent then sends SIGKILL explicitly. The comment
should say "via SIGKILL (after PTRACE_DETACH)".

> +		if (*child->read_ptr != 0) {
> +			tst_res(TFAIL, "Huge zero page was polluted");
> +			child_cleanup();
> +			exit(1);
> +		}

> +	if (WEXITSTATUS(status) != 0) {
> +		/* Tracee reported result and exited early - already handled */
> +		tracee_pid = 0;
> +		free_child_state();
> +		return 1;
> +	}

> +		if (WIFEXITED(status)) {
> +			if (WEXITSTATUS(status) == 0)
> +				tst_brk(TBROK, "Tracee exited unexpectedly: %s",
> +						tst_strstatus(status));
> +
> +			/* Tracee reported result and exited, this is expected for TFAIL */
> +			tracee_exited = 1;
> +			break;
> +		}

The exit code is used to convey "tracee reported a failure" (exit 1)
vs "unexpected exit" (exit 0). LTP rule: never encode pass/fail as a
child exit code; use tst_res() only, and let the framework propagate
the result.

A cleaner approach: add a result_reported field (or similar) to
child_state, set it in the tracee before calling exit(0) on the
failure path, and check that flag in the parent after reaping. The
tracee always exits with 0; the parent distinguishes "reported failure"
from "unexpected exit" via the shared flag.

> +	char path[64];
> +	snprintf(path, sizeof(path), "/proc/%d/mem", tracee_pid);

Path buffers must use PATH_MAX, not a fixed-size literal.

Verdict - Needs revision

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