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

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Message-ID: <20250819073230.9YxJoQY3@linutronix.de>
Date: Tue, 19 Aug 2025 09:32:30 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Waiman Long <longman@...hat.com>
Cc: 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>,
	Shuah Khan <shuah@...nel.org>, 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 2025-08-10 18:27:42 [-0400], 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>

This makes sense.
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Sebastian