Re: [PATCH bpf-next v2] selftests/bpf: Report the real error from libarena parallel workers

[Emil Tsalapatis]

On Thu Jul 23, 2026 at 2:13 AM EDT, Jiayuan Chen wrote:
> Several CI runs failed in the libarena parallel tests with -4 (-EINTR) [1],
> which says nothing about what actually went wrong.
>
> Two workers can fail like this:
>
>   worker 1: gives up, e.g. the rendezvous times out, sets test_abort and
>             returns its own error (-ETIMEDOUT)
>   worker 2: sees test_abort and returns -EINTR
>
> -EINTR only means "someone else already gave up", so it carries no
> information. Which of the two gets reported depends on the order
> pthread_join() collects them, because
>
> 	err = err ?: (long)thread_ret;
>
> keeps the first non-zero value and drops the rest. When the -EINTR worker
> comes first, the error describing the actual failure is lost.
>
> Skip -EINTR entirely: a worker only returns it once another worker has
> already reported the real error, so report and log only the real errors.
>
> It is still unclear whether the timeouts come from CI load or from a
> problem in the test itself. Report the error accurately first, so the next
> failure can be diagnosed.
>
> [1]:
> https://github.com/kernel-patches/bpf/actions/runs/29867905253/job/88764463566
> https://github.com/kernel-patches/bpf/actions/runs/29878191901/job/88794845824
>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>

Reviewed-by: Emil Tsalapatis <emil@xxxxxxxxxxxxxxx>

>
> ---
> v1 -> v2:
> - hoist the worker_err declaration to the top of the function
> - skip -EINTR workers entirely: do not aggregate and do not log them
> - comment/commit message wording fixes
>
> v1: https://lore.kernel.org/bpf/20260722064713.357277-1-jiayuan.chen@xxxxxxxxx/
> ---
>  .../selftests/bpf/prog_tests/libarena.c        | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/libarena.c b/tools/testing/selftests/bpf/prog_tests/libarena.c
> index df7e4b8dc394..daade4150af6 100644
> --- a/tools/testing/selftests/bpf/prog_tests/libarena.c
> +++ b/tools/testing/selftests/bpf/prog_tests/libarena.c
> @@ -73,6 +73,7 @@ static int run_libarena_parallel_test_workers(struct libarena *skel,
>  	uint32_t nthreads;
>  	void *thread_ret;
>  	int ret, err = 0;
> +	int worker_err;
>  	int i;
>  
>  	for (nthreads = 0; nthreads < UINT_MAX; nthreads++) {
> @@ -118,7 +119,22 @@ static int run_libarena_parallel_test_workers(struct libarena *skel,
>  			continue;
>  		}
>  
> -		err = err ?: (long)thread_ret;
> +		worker_err = (long)thread_ret;
> +
> +		/*
> +		 * A worker that bails out because another one already gave up
> +		 * reports -EINTR. It is collateral damage that carries no
> +		 * information, so skip it entirely: never let it become the
> +		 * reported error, and don't log it either.
> +		 */
> +		if (!worker_err || worker_err == -EINTR)
> +			continue;
> +
> +		if (!err)
> +			err = worker_err;
> +
> +		fprintf(stdout, "%.*s__%d returned %d\n", (int)prefixlen, name,
> +			i, worker_err);
>  	}
>  
>  	free(threads);