linux-kernel - Re: [PATCH v2] mm/swapfile: unuse_pte can map random data if swap read fails

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Message-ID: <e2352989-959d-2969-40e4-2d92eb8a5f9b@redhat.com>
Date:   Wed, 20 Apr 2022 09:07:46 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Miaohe Lin <linmiaohe@...wei.com>,
        Alistair Popple <apopple@...dia.com>
Cc:     akpm@...ux-foundation.org, willy@...radead.org, vbabka@...e.cz,
        dhowells@...hat.com, neilb@...e.de, surenb@...gle.com,
        minchan@...nel.org, peterx@...hat.com, sfr@...b.auug.org.au,
        rcampbell@...dia.com, naoya.horiguchi@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/swapfile: unuse_pte can map random data if swap
 read fails

On 20.04.22 08:15, Miaohe Lin wrote:
> On 2022/4/20 8:25, Alistair Popple wrote:
>> Miaohe Lin <linmiaohe@...wei.com> writes:
>>
>>> On 2022/4/19 15:53, Alistair Popple wrote:
>>>> Also in madvise_free_pte_range() you could just remove the swap entry as it's no
>>>> longer needed.
>>>>
>>>
>>> This swap entry will be removed in madvise_dontneed_single_vma().
>>> And in madvise_free_pte_range(), we may need to keep it as same as
>>> hwpoison entry. Or am I supposed to remove it even if hwpoison entry
>>> is reused later?
>>
>> Why would we need to keep it for MADV_FREE though? It only works on private
>> anonymous memory, and once the MADV_FREE operation has succeeded callers can
>> expect they might get zero-fill pages if accessing the memory again. Therefore
>> it should be safe to delete the entry. I think that applies equally to a
>> hwpoison entry too - there's no reason to kill the process if it has called
>> MADV_FREE on the range.
> 
> I tend to agree. We can drop the swapin error entry and hwpoison entry when MADV_FREE
> is called. Should I squash these into the current patch or a separate one is preferred?
> 

That should go into a separate patch.

-- 
Thanks,

David / dhildenb