linux-kernel - Re: [PATCH v9 05/17] mm: mark vmas detached upon exit

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Message-ID: <5d46531b-570b-4f81-90f3-2fb157664f87@lucifer.local>
Date: Mon, 13 Jan 2025 12:05:26 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: akpm@...ux-foundation.org, peterz@...radead.org, willy@...radead.org,
        liam.howlett@...cle.com, david.laight.linux@...il.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, richard.weiyang@...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 v9 05/17] mm: mark vmas detached upon exit

On Fri, Jan 10, 2025 at 08:25:52PM -0800, Suren Baghdasaryan wrote:
> When exit_mmap() removes vmas belonging to an exiting task, it does not
> mark them as detached since they can't be reached by other tasks and they
> will be freed shortly. Once we introduce vma reuse, all vmas will have to
> be in detached state before they are freed to ensure vma when reused is
> in a consistent state. Add missing vma_mark_detached() before freeing the
> vma.

Hmm this really makes me worry that we'll see bugs from this detached
stuff, do we make this assumption anywhere else I wonder?

>
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

But regardless, prima facie, this looks fine, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  mm/vma.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vma.c b/mm/vma.c
> index b9cf552e120c..93ff42ac2002 100644
> --- a/mm/vma.c
> +++ b/mm/vma.c
> @@ -413,10 +413,12 @@ void remove_vma(struct vm_area_struct *vma, bool unreachable)
>  	if (vma->vm_file)
>  		fput(vma->vm_file);
>  	mpol_put(vma_policy(vma));
> -	if (unreachable)
> +	if (unreachable) {
> +		vma_mark_detached(vma);
>  		__vm_area_free(vma);
> -	else
> +	} else {
>  		vm_area_free(vma);
> +	}
>  }
>
>  /*
> --
> 2.47.1.613.gc27f4b7a9f-goog
>