linux-kernel - Re: [PATCH v4 09/14] selftests: harness: Move teardown conditional into test metadata

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Message-ID: <20250612145801.GV543171@nvidia.com>
Date: Thu, 12 Jun 2025 11:58:01 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Nicolin Chen <nicolinc@...dia.com>, Shuah Khan <shuah@...nel.org>,
	Shuah Khan <skhan@...uxfoundation.org>, Willy Tarreau <w@....eu>,
	Thomas Weißschuh <linux@...ssschuh.net>,
	Kees Cook <kees@...nel.org>, Andy Lutomirski <luto@...capital.net>,
	Will Drewry <wad@...omium.org>, Mark Brown <broonie@...nel.org>,
	Muhammad Usama Anjum <usama.anjum@...labora.com>,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 09/14] selftests: harness: Move teardown conditional
 into test metadata

On Thu, Jun 12, 2025 at 04:27:41PM +0200, Thomas Weißschuh wrote:

> If the assumption is that this is most likely a kernel bug,
> shouldn't it be fixed properly rather than worked around?
> After all the job of a selftest is to detect bugs to be fixed.

I investigated the history for a bit and it seems likely we cannot
change the kernel here. Call it an undocumented "feature".

MAP_HUGETLBFS rounds up the length to some value, userspace has to
figure that out and not pass incorrect lengths.  The selftest is doing
that wrong.

> If the test is broken on ARM64 64k in general then I am also wondering how
> it didn't fail before my change to the selftest harness.

It got lucky and didn't overmap something important.

Jason