linux-kernel - Re: [PATCH v2 6/7] mm: add assertion for VMA count limit

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Message-ID: <322fd5d2-d7f4-40d8-8a06-6e7c5e9ef180@redhat.com>
Date: Wed, 17 Sep 2025 20:34:10 +0200
From: David Hildenbrand <david@...hat.com>
To: Kalesh Singh <kaleshsingh@...gle.com>
Cc: akpm@...ux-foundation.org, minchan@...nel.org,
 lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, rppt@...nel.org,
 pfalcato@...e.de, kernel-team@...roid.com, android-mm@...gle.com,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Kees Cook <kees@...nel.org>, Vlastimil Babka <vbabka@...e.cz>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
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 <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
 Valentin Schneider <vschneid@...hat.com>, Jann Horn <jannh@...gle.com>,
 Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-trace-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 6/7] mm: add assertion for VMA count limit

>> Can't that fire when changing the max count from user space at just the
>> wrong time?
> 
> You are right: technically it's possible if it was raised between the
> time of checking and when the new VMA is added.
> 
>>
>> I assume we'll have to tolerated that and might just want to drop this
>> patch from the series.
>>
> 
> It is compiled out in !CONFIG_VM_DEBUG builds, would we still want to drop it?

Due to the racy nature I think any kinds of assertions would be wrong. 
Without any such races possible I would agree that the checks would be 
nice to have.

-- 
Cheers

David / dhildenb