linux-kernel - Re: [PATCH v2] mm/page_isolation: don't putback unisolated page

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Message-ID: <bcba5a70-369b-ce8a-ca83-968ab3c14969@huawei.com>
Date:   Mon, 13 Sep 2021 20:37:21 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     David Hildenbrand <david@...hat.com>, <akpm@...ux-foundation.org>
CC:     <jhubbard@...dia.com>, <vbabka@...e.cz>, <iamjoonsoo.kim@....com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm/page_isolation: don't putback unisolated page

On 2021/9/13 20:15, David Hildenbrand wrote:
> On 13.09.21 13:50, Miaohe Lin wrote:
>> If __isolate_free_page() failed, due to zone watermark check, the page is
>> still on the free list. But this page will be put back to free list again
>> via __putback_isolated_page() now. This may trigger page->flags checks in
>> __free_one_page() if PageReported is set. Or we will corrupt the free list
>> because list_add() will be called for pages already on another list.
>>
>> Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock")
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>> ---
>> v1->v2:
>>    Add VM_WARN_ON to catch unexpected isolating failure.
>> ---
>>   mm/page_isolation.c | 9 +++++++--
>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>> index f93cc63d8fa1..f67c4c70f17f 100644
>> --- a/mm/page_isolation.c
>> +++ b/mm/page_isolation.c
>> @@ -94,8 +94,13 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
>>               buddy = page + (buddy_pfn - pfn);
>>                 if (!is_migrate_isolate_page(buddy)) {
>> -                __isolate_free_page(page, order);
>> -                isolated_page = true;
>> +                isolated_page = !!__isolate_free_page(page, order);
>> +                /*
>> +                 * Isolating a free page in an isolated pageblock
>> +                 * is expected to always work as watermarks don't
>> +                 * apply here.
>> +                 */
>> +                VM_WARN_ON(!isolated_page);
> 
> 
> Didn't we discuss that this can never happen?
> 
> In that case, the patch description+subject needs updating and the "Fixes" line would be wrong.
> 

I thought this might need a Fixes tag... Will change all of these. Many thanks.

>>               }
>>           }
>>       }
>>
> 
>