linux-kernel - Re: [PATCH] selftests/sched_ext: Fix exit selftest hang on UP

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Message-ID: <20250701130022.GA26180@pauld.westford.csb>
Date: Tue, 1 Jul 2025 09:00:22 -0400
From: Phil Auld <pauld@...hat.com>
To: Andrea Righi <arighi@...dia.com>
Cc: Tejun Heo <tj@...nel.org>, David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/sched_ext: Fix exit selftest hang on UP

On Tue, Jul 01, 2025 at 08:08:45AM +0200 Andrea Righi wrote:
> On single-CPU systems, ops.select_cpu() is never called, causing the
> EXIT_SELECT_CPU test case to wait indefinitely.
> 
> Avoid the stall by skipping this specific sub-test when only one CPU is
> available.
> 
> Reported-by: Phil Auld <pauld@...hat.com>
> Fixes: a5db7817af780 ("sched_ext: Add selftests")
> Signed-off-by: Andrea Righi <arighi@...dia.com>


Thanks Andrea! You beat me to it. I didn't know that libbpf
call existed :)

Reviewed-by: Phil Auld <pauld@...hat.com>

and

Tested-by: Phil Auld <pauld@...hat.com>


Cheers,
Phil

> ---
>  tools/testing/selftests/sched_ext/exit.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/tools/testing/selftests/sched_ext/exit.c b/tools/testing/selftests/sched_ext/exit.c
> index 9451782689de1..ee25824b1cbe6 100644
> --- a/tools/testing/selftests/sched_ext/exit.c
> +++ b/tools/testing/selftests/sched_ext/exit.c
> @@ -22,6 +22,14 @@ static enum scx_test_status run(void *ctx)
>  		struct bpf_link *link;
>  		char buf[16];
>  
> +		/*
> +		 * On single-CPU systems, ops.select_cpu() is never
> +		 * invoked, so skip this test to avoid getting stuck
> +		 * indefinitely.
> +		 */
> +		if (tc == EXIT_SELECT_CPU && libbpf_num_possible_cpus() == 1)
> +			continue;
> +
>  		skel = exit__open();
>  		SCX_ENUM_INIT(skel);
>  		skel->rodata->exit_point = tc;
> -- 
> 2.50.0
> 

--