linux-kernel - Re: [PATCH] selftests/futex: Fix some futex_numa

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Message-ID: <86ace13c-b9fd-42e3-84e5-e3716ca21645@redhat.com>
Date: Mon, 18 Aug 2025 11:54:32 -0400
From: Waiman Long <llong@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Darren Hart <dvhart@...radead.org>,
 Davidlohr Bueso <dave@...olabs.net>, André Almeida
 <andrealmeid@...lia.com>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Shuah Khan <shuah@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
 Colin Ian King <colin.i.king@...il.com>
Subject: Re: [PATCH] selftests/futex: Fix some futex_numa_mpol subtests

On 8/10/25 6:27 PM, Waiman Long wrote:
> The "Memory out of range" subtest of futex_numa_mpol assumes that memory
> access outside of the mmap'ed area is invalid. That may not be the case
> depending on the actual memory layout of the test application. When
> that subtest was run on an x86-64 system with latest upstream kernel,
> the test passed as an error was returned from futex_wake(). On another
> powerpc system, the same subtest failed because futex_wake() returned 0.
>
>    Bail out! futex2_wake(64, 0x86) should fail, but didn't
>
> Looking further into the passed subtest on x86-64, it was found that an
> -EINVAL was returned instead of -EFAULT. The -EINVAL error was returned
> because the node value test with FLAGS_NUMA set failed with a node value
> of 0x7f7f. IOW, the futex memory was accessible and futex_wake() failed
> because the supposed node number wasn't valid. If that memory location
> happens to have a very small value (e.g. 0), the test will pass and no
> error will be returned.
>
> Since this subtest is non-deterministic, it is dropped unless we
> explicitly set a guard page beyond the mmap region.
>
> The other problematic test is the "Memory too small" test. The
> futex_wake() function returns the -EINVAL error code because the given
> futex address isn't 8-byte aligned, not because only 4 of the 8 bytes
> are valid and the other 4 bytes are not. So proper name of this subtest
> is changed to "Mis-aligned futex" to reflect the reality.
>
> Fixes: 3163369407ba ("selftests/futex: Add futex_numa_mpol")
> Signed-off-by: Waiman Long <longman@...hat.com>

Ping! Any comment or suggested change?

-Longman

> ---
>   tools/testing/selftests/futex/functional/futex_numa_mpol.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/futex/functional/futex_numa_mpol.c b/tools/testing/selftests/futex/functional/futex_numa_mpol.c
> index a9ecfb2d3932..802c15c82190 100644
> --- a/tools/testing/selftests/futex/functional/futex_numa_mpol.c
> +++ b/tools/testing/selftests/futex/functional/futex_numa_mpol.c
> @@ -182,12 +182,10 @@ int main(int argc, char *argv[])
>   	if (futex_numa->numa == FUTEX_NO_NODE)
>   		ksft_exit_fail_msg("NUMA node is left uninitialized\n");
>   
> -	ksft_print_msg("Memory too small\n");
> +	/* FUTEX2_NUMA futex must be 8-byte aligned */
> +	ksft_print_msg("Mis-aligned futex\n");
>   	test_futex(futex_ptr + mem_size - 4, 1);
>   
> -	ksft_print_msg("Memory out of range\n");
> -	test_futex(futex_ptr + mem_size, 1);
> -
>   	futex_numa->numa = FUTEX_NO_NODE;
>   	mprotect(futex_ptr, mem_size, PROT_READ);
>   	ksft_print_msg("Memory, RO\n");