linux-kernel - Re: [PATCH v3] staging: kpc2000: Convert put_page to put_user

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Date:   Fri, 19 Jul 2019 14:05:23 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Matt Sickler <Matt.Sickler@...tronics.com>,
        Bharath Vedartham <linux.bhar@...il.com>,
        "ira.weiny@...el.com" <ira.weiny@...el.com>,
        "jglisse@...hat.com" <jglisse@...hat.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>
Subject: Re: [PATCH v3] staging: kpc2000: Convert put_page to put_user_page*()

On 7/19/19 1:59 PM, Matt Sickler wrote:
>> From: Bharath Vedartham <linux.bhar@...il.com>
>> Changes since v2
>>        - Added back PageResevered check as suggested by John Hubbard.
>>
>> The PageReserved check needs a closer look and is not worth messing
>> around with for now.
>>
>> Matt, Could you give any suggestions for testing this patch?
> 
> Myself or someone else from Daktronics would have to do the testing since the
> hardware isn't really commercially available.  I've been toying with the idea
> of asking for a volunteer from the mailing list to help me out with this - I'd
> send them some hardware and they'd do all the development and testing. :)
> I still have to run that idea by Management though.
> 
>> If in-case, you are willing to pick this up to test. Could you
>> apply this patch to this tree and test it with your devices?
> 
> I've been meaning to get to testing the changes to the drivers since upstreaming
> them, but I've been swamped with other development.  I'm keeping an eye on the
> mailing lists, so I'm at least aware of what is coming down the pipe.
> I'm not too worried about this specific change, even though I don't really know
> if the reserved check and the dirtying are even necessary.
> It sounded like John's suggestion was to not do the PageReserved() check and just
> use put_user_pges_dirty() all the time.  John, is that incorrect?
> 

That's what I suggested at first. But then I saw at least one other place where 
this pattern is being used, and it shook my confidence. I don't clearly see what
the PageReserved check is protecting against here, but it's better to be
safe, and do things in two steps: step 1 is *only* convert from put_page()
to put_user_page(), and step 2 is to maybe remove the PageReserved() check,
once fully understood. 


thanks,
-- 
John Hubbard
NVIDIA