linux-kernel - Re: [PATCH mm-unstable v14 03/16] introduce collapse_single_pmd to unify khugepaged and madvise

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Message-ID: <7e666361-24cd-4eb4-a591-73a8900bdb5c@lucifer.local>
Date: Mon, 26 Jan 2026 12:25:41 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: Lance Yang <lance.yang@...ux.dev>, Nico Pache <npache@...hat.com>,
        akpm@...ux-foundation.org, david@...nel.org, ziy@...dia.com,
        Liam.Howlett@...cle.com, ryan.roberts@....com, dev.jain@....com,
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        richard.weiyang@...il.com, David Hildenbrand <david@...hat.com>,
        linux-mm@...ck.org
Subject: Re: [PATCH mm-unstable v14 03/16] introduce collapse_single_pmd to
 unify khugepaged and madvise_collapse

On Fri, Jan 23, 2026 at 05:31:17PM +0800, Baolin Wang wrote:
>
>
> On 1/23/26 1:07 PM, Lance Yang wrote:
> >
> >
> > After collapse_single_pmd() returns, mmap_lock might have been released.
> > Between
> > that unlock and here, another thread could unmap/remap the VMA, making
> > the vma
> > pointer stale when we access vma->vm_file?
> >
> > Would it be safer to get the file reference before calling
> > collapse_single_pmd()?
> > Or we need to revalidate the VMA after getting the lock back?
> Good catch. I think we can move the filemap_write_and_wait_range() related
> logic into collapse_single_pmd(), after we get a file reference.

Good suggestion, is what Nico did in the suggested patch :) Agreed better there.

Thanks, Lorenzo