linux-kernel - Re: [PATCH v5 3/6] mm: mark vma as detached until it's added into vma tree

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Message-ID: <aafe0538-0c56-469e-b23b-3f22cb8186a0@suse.cz>
Date: Tue, 10 Dec 2024 12:36:16 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
Cc: willy@...radead.org, liam.howlett@...cle.com, lorenzo.stoakes@...cle.com,
 mhocko@...e.com, 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,
 minchan@...gle.com, jannh@...gle.com, shakeel.butt@...ux.dev,
 souravpanda@...gle.com, pasha.tatashin@...een.com, corbet@....net,
 linux-doc@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 kernel-team@...roid.com
Subject: Re: [PATCH v5 3/6] mm: mark vma as detached until it's added into vma
 tree

On 12/6/24 23:52, Suren Baghdasaryan wrote:
> Current implementation does not set detached flag when a VMA is first
> allocated. This does not represent the real state of the VMA, which is
> detached until it is added into mm's VMA tree. Fix this by marking new
> VMAs as detached and resetting detached flag only after VMA is added
> into a tree.
> Introduce vma_mark_attached() to make the API more readable and to
> simplify possible future cleanup when vma->vm_mm might be used to
> indicate detached vma and vma_mark_attached() will need an additional
> mm parameter.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> Reviewed-by: Shakeel Butt <shakeel.butt@...ux.dev>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> diff --git a/kernel/fork.c b/kernel/fork.c
> index 21660a9ad97a..71990f46aa4e 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -465,6 +465,10 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
>  	data_race(memcpy(new, orig, sizeof(*new)));
>  	vma_lock_init(new);
>  	INIT_LIST_HEAD(&new->anon_vma_chain);
> +#ifdef CONFIG_PER_VMA_LOCK
> +	/* vma is not locked, can't use vma_mark_detached() */
> +	new->detached = true;
> +#endif

It occured me we could probably move the detached setting to vma_lock_init()
to avoid the #ifdef (also in the ctor in next patch)?

>  	vma_numab_state_init(new);
>  	dup_anon_vma_name(orig, new);
>