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

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Message-ID: <CAC_TJvf84Zerwe7-UiRW3AYnC=_Zu3tVSSWTRcaEyoRGEnBHug@mail.gmail.com>
Date: Wed, 17 Sep 2025 13:31:37 -0700
From: Kalesh Singh <kaleshsingh@...gle.com>
To: David Hildenbrand <david@...hat.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>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Ben Segall <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

On Wed, Sep 17, 2025 at 11:34 AM David Hildenbrand <david@...hat.com> wrote:
>
> >> 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.

Alright I'll drop this in the next revision.

Thanks,
Kalesh

>
> --
> Cheers
>
> David / dhildenb
>