linux-kernel - Re: [PATCH] mm/page_isolation: fix potential missing call to unset_migratetype

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Date:   Mon, 6 Sep 2021 11:46:49 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     mhocko@...e.com, vbabka@...e.cz, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_isolation: fix potential missing call to
 unset_migratetype_isolate()

On 06.09.21 11:38, Miaohe Lin wrote:
> On 2021/9/6 17:27, David Hildenbrand wrote:
>> On 04.09.21 11:20, Miaohe Lin wrote:
>>> In start_isolate_page_range() undo path, pfn_to_online_page() just checks
>>> the first pfn in a pageblock while __first_valid_page() will traverse the
>>> pageblock until the first online pfn is found. So we may miss the call to
>>> unset_migratetype_isolate() in undo path and pages will remain isolated
>>> unexpectedly. Fix this by calling undo_isolate_page_range() and this will
>>> also help to remove some duplicated codes.
>>>
>>> Fixes: 2ce13640b3f4 ("mm: __first_valid_page skip over offline pages")
>>
>> While that is true, we shouldn't ever trigger, neither via cma, virtio-mem nor memory offlining, because essentially all operate on MAX_ORDER -1 -aligned ranges without memory holes.
> 
> I think this should never trigger too. It's a theoretical issue. So is the Fixes tag necessary ?
> 

I think it's one of these "let's add Fixes: but no need for Cc: stable".

BUT in older kernels we could have triggered this via memory offlining 
eventually ... before c5e79ef561b0 ("mm/memory_hotplug.c: don't allow to 
online/offline memory blocks with holes") ... so maybe even a Cc: stable?

-- 
Thanks,

David / dhildenb