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Date: Mon, 3 Aug 2026 14:09:24 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Hongfu Li <hongfu.li@linux.dev>
Cc: shuah@kernel.org, richard.weiyang@gmail.com,
 reddybalavignesh9979@gmail.com, linux-kselftest@vger.kernel.org,
 linux-kernel@vger.kernel.org, Hongfu Li <lihongfu@kylinos.cn>
Subject: Re: [PATCH] selftests/prctl: Fix non-anonymous VMA mapping in
 set-anon-vma-name test
Message-Id: <20260803140924.31bf563743a73653f65e2258@linux-foundation.org>
In-Reply-To: <20260803103046.14324-1-hongfu.li@linux.dev>
References: <20260803103046.14324-1-hongfu.li@linux.dev>
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On Mon,  3 Aug 2026 18:30:46 +0800 Hongfu Li <hongfu.li@linux.dev> wrote:

> The test creates a non-anonymous VMA (ptr_not_anon) via mmap() with
> MAP_PRIVATE but without MAP_ANONYMOUS, using fd=0 (stdin) as the file
> descriptor.  This always fails because fd=0 is not a regular file,
> and the failure was hidden because ASSERT_NE() incorrectly checked
> for NULL instead of MAP_FAILED.

It's remarkable how often code assumes that mmap(...)==NULL is the
error return.

> Fix by using mkstemp() + ftruncate() to create a real temporary file,
> then mapping it with MAP_PRIVATE to obtain a genuine file-backed VMA.
> Also fix the mmap() error checks to use MAP_FAILED instead of NULL,
> and pass fd=-1 for the anonymous mapping for clarity.  The temp file
> is unlinked immediately so it does not persist on disk.

Thanks.

AI review found one glitch which I don't think we need to care about:
	https://sashiko.dev/#/patchset/20260803103046.14324-1-hongfu.li@linux.dev

and one possible pre-existing issue which is kinda related and which
you may choose to address.  Please take a look and let us know?