linux-kernel - Re: [PATCH v7 1/7] selftests/proc: add /proc/pid/maps tearing from vma split test

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Message-ID: <f041e611-9d28-4a30-8515-97080f742360@redhat.com>
Date: Wed, 16 Jul 2025 12:44:23 +0200
From: David Hildenbrand <david@...hat.com>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
Cc: Liam.Howlett@...cle.com, lorenzo.stoakes@...cle.com, vbabka@...e.cz,
 peterx@...hat.com, jannh@...gle.com, hannes@...xchg.org, mhocko@...nel.org,
 paulmck@...nel.org, shuah@...nel.org, adobriyan@...il.com,
 brauner@...nel.org, josef@...icpanda.com, yebin10@...wei.com,
 linux@...ssschuh.net, willy@...radead.org, osalvador@...e.de,
 andrii@...nel.org, ryan.roberts@....com, christophe.leroy@...roup.eu,
 tjmercier@...gle.com, kaleshsingh@...gle.com, aha310510@...il.com,
 linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v7 1/7] selftests/proc: add /proc/pid/maps tearing from
 vma split test

On 16.07.25 05:05, Suren Baghdasaryan wrote:
> The /proc/pid/maps file is generated page by page, with the mmap_lock
> released between pages.  This can lead to inconsistent reads if the
> underlying vmas are concurrently modified. For instance, if a vma split
> or merge occurs at a page boundary while /proc/pid/maps is being read,
> the same vma might be seen twice: once before and once after the change.
> This duplication is considered acceptable for userspace handling.
> However, observing a "hole" where a vma should be (e.g., due to a vma
> being replaced and the space temporarily being empty) is unacceptable.
> 
> Implement a test that:
> 1. Forks a child process which continuously modifies its address space,
> specifically targeting a vma at the boundary between two pages.
> 2. The parent process repeatedly reads the child's /proc/pid/maps.
> 3. The parent process checks the last vma of the first page and
> the first vma of the second page for consistency, looking for the
> effects of vma splits or merges.
> 
> The test duration is configurable via the -d command-line parameter
> in seconds to increase the likelihood of catching the race condition.
> The default test duration is 5 seconds.
> 
> Example Command: proc-maps-race -d 10
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>

Why is this selftest not making use of any kselftest framework?

I'm sure there is a very good reason :)

Reading assert() feels very weird compared to other selftests.

-- 
Cheers,

David / dhildenb