linux-kernel - Re: [PATCH] mm: swap: check for xa_zero

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Message-ID: <c63b9a78-6a39-42e1-8a72-b4ce4a7025b1@redhat.com>
Date: Mon, 11 Aug 2025 17:51:11 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Charan Teja Kalla <quic_charante@...cinc.com>, akpm@...ux-foundation.org,
 shikemeng@...weicloud.com, kasong@...cent.com, nphamcs@...il.com,
 bhe@...hat.com, baohua@...nel.org, chrisl@...nel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] mm: swap: check for xa_zero_entry() on vma in swapoff
 path

On 11.08.25 17:48, Lorenzo Stoakes wrote:
> On Mon, Aug 11, 2025 at 05:39:32PM +0200, David Hildenbrand wrote:
>>
>>>
>>> I could make a function that frees all new vmas and destroys the tree
>>> specifically for this failure state?
>>
>> I think the problem is that some page tables were already copied, so we
>> would have to zap them as well.
> 
> This shouldn't be too much more egregious?
> 
> The issues arise when it might be an OOM issue, but if it's a fatal signal we
> can take the time to clean up.
> 
>>
>> Maybe just factoring stuff from the exit_mmap() function could be one way to
>> do it.
> 
> Is exit_mmap() a problem here? Or maybe I don't understand what you're getting
> at.

We are dropping the write lock in between, allowing for these races.

-- 
Cheers,

David / dhildenb