linux-kernel - Re: [PATCH v10 04/18] mm: introduce vma_iter_store

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Message-ID: <9854b4f2-3482-415c-8e1b-46cb4a2650b2@suse.cz>
Date: Fri, 21 Feb 2025 12:07:02 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
Cc: peterz@...radead.org, willy@...radead.org, liam.howlett@...cle.com,
 lorenzo.stoakes@...cle.com, david.laight.linux@...il.com, mhocko@...e.com,
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 linux-doc@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH v10 04/18] mm: introduce vma_iter_store_attached() to use
 with attached vmas

On 2/13/25 23:46, Suren Baghdasaryan wrote:
> vma_iter_store() functions can be used both when adding a new vma and
> when updating an existing one. However for existing ones we do not need
> to mark them attached as they are already marked that way. With
> vma->detached being a separate flag, double-marking a vmas as attached
> or detached is not an issue because the flag will simply be overwritten
> with the same value. However once we fold this flag into the refcount
> later in this series, re-attaching or re-detaching a vma becomes an
> issue since these operations will be incrementing/decrementing a
> refcount.
> Introduce vma_iter_store_new() and vma_iter_store_overwrite() to replace
> vma_iter_store() and avoid re-attaching a vma during vma update. Add
> assertions in vma_mark_attached()/vma_mark_detached() to catch invalid
> usage. Update vma tests to check for vma detached state correctness.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

> ---
> Changes since v9 [1]:
> - Change VM_BUG_ON_VMA() to WARN_ON_ONCE() in vma_assert_{attached|detached},
> per Lorenzo Stoakes

Maybe later we can reduce the paranoia to VM_WARN_ON_ONCE()?