linux-kernel - Re: [PATCH v11 00/25] mm/gup: track dma-pinned pages: FOLL

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Date:   Mon, 6 Jan 2020 17:26:16 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Jan Kara <jack@...e.cz>
CC:     Leon Romanovsky <leon@...nel.org>, Jason Gunthorpe <jgg@...pe.ca>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Alex Williamson" <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ira Weiny <ira.weiny@...el.com>, Jens Axboe <axboe@...nel.dk>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...e.com>,
        "Mike Kravetz" <mike.kravetz@...cle.com>,
        Paul Mackerras <paulus@...ba.org>,
        "Shuah Khan" <shuah@...nel.org>, Vlastimil Babka <vbabka@...e.cz>,
        <bpf@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <kvm@...r.kernel.org>, <linux-block@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>, <linux-media@...r.kernel.org>,
        <linux-rdma@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
        <netdev@...r.kernel.org>, <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Maor Gottlieb <maorg@...lanox.com>,
        "Ran Rozenstein" <ranro@...lanox.com>
Subject: Re: [PATCH v11 00/25] mm/gup: track dma-pinned pages: FOLL_PIN

On 1/6/20 1:01 AM, Jan Kara wrote:
...
>> Also, looking ahead:
>>
>> a) if the problem disappears with the latest above test, then we likely have
>>     a huge page refcount overflow, and there are a couple of different ways to
>>     fix it.
>>
>> b) if it still reproduces with the above, then it's some other random mistake,
>>     and in that case I'd be inclined to do a sort of guided (or classic, unguided)
>>     git bisect of the series. Because it could be any of several patches.
>>
>>     If that's too much trouble, then I'd have to fall back to submitting a few
>>     patches at a time and working my way up to the tracking patch...
> 
> It could also be that an ordinary page reference is dropped with 'unpin'
> thus underflowing the page refcount...
> 
> 								Honza
> 

Yes.

And, I think I'm about out of time for this release cycle, so I'm probably going to
submit the prerequisite patches (patches 1-10, or more boldly, 1-22), for candidates
for 5.6.


thanks,
-- 
John Hubbard
NVIDIA