linux-kernel - Re: [PATCH v3 1/1] mm: introduce put_user

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Date:   Wed, 13 Mar 2019 20:19:08 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Ira Weiny <ira.weiny@...el.com>
CC:     <john.hubbard@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <linux-mm@...ck.org>, Al Viro <viro@...iv.linux.org.uk>,
        Christian Benvenuti <benve@...co.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christopher Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>,
        Doug Ledford <dledford@...hat.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jerome Glisse <jglisse@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Tom Talpey <tom@...pey.com>,
        LKML <linux-kernel@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v3 1/1] mm: introduce put_user_page*(), placeholder
 versions

On 3/13/19 7:49 AM, Ira Weiny wrote:
> On Tue, Mar 12, 2019 at 05:38:55PM -0700, John Hubbard wrote:
>> On 3/12/19 8:30 AM, Ira Weiny wrote:
>>> On Wed, Mar 06, 2019 at 03:54:55PM -0800, john.hubbard@...il.com wrote:
>>>> From: John Hubbard <jhubbard@...dia.com>
>>>>
>>>> Introduces put_user_page(), which simply calls put_page().
>>>> This provides a way to update all get_user_pages*() callers,
>>>> so that they call put_user_page(), instead of put_page().
>>>
>>> So I've been running with these patches for a while but today while ramping up
>>> my testing I hit the following:
>>>
>>> [ 1355.557819] ------------[ cut here ]------------
>>> [ 1355.563436] get_user_pages pin count overflowed
>>
>> Hi Ira,
>>
>> Thanks for reporting this. That overflow, at face value, means that we've
>> used more than the 22 bits worth of gup pin counts, so about 4 million pins
>> of the same page...
> 
> This is my bug in the patches I'm playing with.  Somehow I'm causing more puts
> than gets...  I'm not sure how but this is for sure my problem.
> 
> Backing off to your patch set the numbers are good.

Now that's a welcome bit of good news!

> 
> Sorry for the noise.
> 
> With the testing I've done today I feel comfortable adding
> 
> Tested-by: Ira Weiny <ira.weiny@...el.com>
> 
> For the main GUP and InfiniBand patches.
> 
> Ira
> 

OK, I'll add your tested-by tag to patches 1, 2, 4, 5 (the numbering refers
to the "RFC v2: mm: gup/dma tracking" posting [1]) in my repo [2], and they'll 
show up in the next posting. (Patch 3 is already upstream, and patch 6 is
documentation that needs to be rewritten entirely.)

[1] https://lore.kernel.org/r/20190204052135.25784-1-jhubbard@nvidia.com

[2] https://github.com/johnhubbard/linux/tree/gup_dma_core

thanks,
-- 
John Hubbard
NVIDIA