netdev - Re: [PATCH 20/34] xen: convert put_page() to put_user

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Date:   Fri, 2 Aug 2019 12:25:01 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     "Weiny, Ira" <ira.weiny@...el.com>,
        Juergen Gross <jgross@...e.com>,
        "john.hubbard@...il.com" <john.hubbard@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
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        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
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        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
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        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH 20/34] xen: convert put_page() to put_user_page*()

On 8/2/19 9:09 AM, Weiny, Ira wrote:
>>
>> On 02.08.19 07:48, John Hubbard wrote:
>>> On 8/1/19 9:36 PM, Juergen Gross wrote:
>>>> On 02.08.19 04:19, john.hubbard@...il.com wrote:
>>>>> From: John Hubbard <jhubbard@...dia.com>
>>> ...
>>> If that's not the case (both here, and in 3 or 4 other patches in this
>>> series, then as you said, I should add NULL checks to put_user_pages()
>>> and put_user_pages_dirty_lock().
>>
>> In this case it is not correct, but can easily be handled. The NULL case can
>> occur only in an error case with the pages array filled partially or not at all.
>>
>> I'd prefer something like the attached patch here.
> 
> I'm not an expert in this code and have not looked at it carefully but that patch does seem to be the better fix than forcing NULL checks on everyone.
> 

OK, I'll use Juergen's approach, and also check for that pattern in the
other patches.


thanks,
-- 
John Hubbard
NVIDIA