linux-kernel - Re: [PATCH v6 10/16] mm: replace vm_lock and detached flag with a reference count

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Message-ID: <20241219085515.GB26551@noisy.programming.kicks-ass.net>
Date: Thu, 19 Dec 2024 09:55:15 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>, akpm@...ux-foundation.org,
	willy@...radead.org, lorenzo.stoakes@...cle.com, mhocko@...e.com,
	vbabka@...e.cz, hannes@...xchg.org, mjguzik@...il.com,
	oliver.sang@...el.com, mgorman@...hsingularity.net,
	david@...hat.com, peterx@...hat.com, oleg@...hat.com,
	dave@...olabs.net, paulmck@...nel.org, brauner@...nel.org,
	dhowells@...hat.com, hdanton@...a.com, hughd@...gle.com,
	lokeshgidra@...gle.com, minchan@...gle.com, jannh@...gle.com,
	shakeel.butt@...ux.dev, souravpanda@...gle.com,
	pasha.tatashin@...een.com, klarasmodin@...il.com, corbet@....net,
	linux-doc@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v6 10/16] mm: replace vm_lock and detached flag with a
 reference count

On Wed, Dec 18, 2024 at 11:29:23AM -0800, Suren Baghdasaryan wrote:

> Yeah, I think we can simply do this:
> 
> vms_complete_munmap_vmas
>            vms_clear_ptes
>            remove_vma
>                vma_mark_detached
>            mmap_write_downgrade
> 
> If my assumption is incorrect, assertion inside vma_mark_detached()
> should trigger. I tried a quick test and so far nothing exploded.

I think that would be unfortunate and could cause regressions. I think
we want to keep vms_clear_ptes() under the read-lock.