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Subject: Re: [PATCH STABLE 4.4 5/8] mm: prevent get_user_pages() from
 overflowing page refcount
To:     Ajay Kaher <akaher@vmware.com>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Cc:     "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jann Horn <jannh@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        "stable@kernel.org" <stable@kernel.org>,
        Srivatsa Bhat <srivatsab@vmware.com>,
        "srivatsa@csail.mit.edu" <srivatsa@csail.mit.edu>,
        Vasavi Sirnapalli <vsirnapalli@vmware.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
References: <20191108093814.16032-1-vbabka@suse.cz>
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From:   Vlastimil Babka <vbabka@suse.cz>
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Message-ID: <ac76f388-9a73-b055-419a-37f182211343@suse.cz>
Date:   Mon, 9 Dec 2019 10:10:01 +0100
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Sender: linux-kernel-owner@vger.kernel.org
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On 12/9/19 9:54 AM, Ajay Kaher wrote:
> 
> 
> ﻿On 06/12/19, 8:02 PM, "Vlastimil Babka" <vbabka@suse.cz> wrote:
> 
>> On 12/6/19 5:15 AM, Ajay Kaher wrote:
>>>
>>>
>>> On 03/12/19, 6:28 PM, "Vlastimil Babka" <vbabka@suse.cz> wrote:
>>>>>>    
>>>>>> [ 4.4 backport: there's get_page_foll(), so add try_get_page()-like checks
>>>>>>                 in there, enabled by a new parameter, which is false where
>>>>>>                 upstream patch doesn't replace get_page() with try_get_page()
>>>>>>                 (the THP and hugetlb callers).
>>>>>
>>>>> Could we have try_get_page_foll(), as in:
>>>>> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fstable%2F1570581863-12090-3-git-send-email-akaher%40vmware.com%2F&amp;data=02%7C01%7Cakaher%40vmware.com%7Cb65cf5622ca8401fd2ba08d77a5914e8%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637112395344338606&amp;sdata=sLbw%2BQWu0%2BB0y2OpfaQS%2FxXX6Z9jNB3wPeTcPsawNJA%3D&amp;reserved=0
>>>>>
>>>>> + Code will be in sync as we have try_get_page()
>>>>> + No need to add extra argument to try_get_page()
>>>>> + No need to modify the callers of try_get_page()
>>>
>>> Any reason for not using try_get_page_foll().
>>    
>> Ah, sorry, I missed that previously. It's certainly possible to do it
>> that way, I just didn't care so strongly to rewrite the existing SLES
>> patch. It's a stable backport for a rather old LTS, not a codebase for
>> further development.
>  
> Thanks for your response.
> 
> I would appreciate if you would like to include try_get_page_foll(),
> and resend this patch series again.

I won't have time for that now, but I don't mind if you do that, or
resend your version with the missing x86 and s390 gup.c parts and
preferably without 7aef4172c795.