linux-kernel - Re: [PATCH v2 6/8] mm: prevent get_user_pages() from overflowing page refcount

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Date:   Fri, 29 Nov 2019 10:08:57 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Ajay Kaher <akaher@...are.com>
Cc:     "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "punit.agrawal@....com" <punit.agrawal@....com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "will.deacon@....com" <will.deacon@....com>,
        "mszeredi@...hat.com" <mszeredi@...hat.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Srivatsa Bhat <srivatsab@...are.com>,
        "srivatsa@...il.mit.edu" <srivatsa@...il.mit.edu>,
        Alexey Makhalov <amakhalov@...are.com>,
        Srinidhi Rao <srinidhir@...are.com>,
        Vikash Bansal <bvikas@...are.com>,
        Anish Swaminathan <anishs@...are.com>,
        Vasavi Sirnapalli <vsirnapalli@...are.com>,
        Steven Rostedt <srostedt@...are.com>,
        "stable@...nel.org" <stable@...nel.org>,
        Ben Hutchings <ben@...adent.org.uk>
Subject: Re: [PATCH v2 6/8] mm: prevent get_user_pages() from overflowing page
 refcount

On 11/21/19 9:38 PM, gregkh@...uxfoundation.org wrote:
> On Mon, Nov 11, 2019 at 05:00:29AM +0000, Ajay Kaher wrote:
>>
>> On 06/11/19, 2:25 PM, "Vlastimil Babka" <vbabka@...e.cz> wrote:
>>
>>> On 10/25/19 8:18 AM, Ajay Kaher wrote:
>>>> On 17/10/19, 9:58 PM, "Ajay Kaher" <akaher@...are.com> wrote:
>>>>     
>>>>>    
>>>>> Could we handle arch-specific gup.c in different patch sets and 
>>>>> let these patches to merge to 4.4.y?
>>>>   
>>>> Vlastimil, please suggest if it's fine to merge these patches to 4.4.y
>>>
>>> I'm not sure if it makes much sense to merge them without the arch-specific gup
>>> support, when we're aware that it's missing.
>>>
>>>> and handle arch-specific gup.c in different patch sets starts from 4.19.y,
>>>
>>> Actually arch-specific gup.c were removed in 4.13, so it's enough to start from
>>> 4.9.y, which I'm going to finally look into.
>>
>> Yes x86 gup.c is removed. s390 gup.c is present till 4.19,
>> so if you are making changes in this file for 4.4.y and 4.9.y, 
>> then same should be done for 4.14.y and v4.19.y.
> 
> Ok, I have no idea what to do here.  I have two different series from
> both of you, yet they are different.
> 
> Can you both come up with a series you agree on, and send it to me, with
> both of your acks so that I know this is what should be applied?  I've
> deleted both of your current series from my todo mbox.

I started by fixing up [1] 4.9, 4.14 and 4.19 which already got the
backport, but without arch-specific gup.c variants. I'll wait for Ajay's
feedback for the 4.4 series.

[1] https://lore.kernel.org/linux-mm/20191129090351.3507-1-vbabka@suse.cz/

> thanks,
> 
> greg k-h
>