linux-kernel - Re: [PATCH v8 17/26] media/v4l2-core: set pages dirty upon releasing DMA buffers

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Message-ID: <fc100f4b-2c14-b56b-488a-e2d54d61d575@nvidia.com>
Date:   Mon, 9 Dec 2019 21:48:24 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     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>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, 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>,
        Christoph Hellwig <hch@....de>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        <stable@...r.kernel.org>
Subject: Re: [PATCH v8 17/26] media/v4l2-core: set pages dirty upon releasing
 DMA buffers

On 12/9/19 4:56 PM, Andrew Morton wrote:
> On Mon, 9 Dec 2019 14:53:35 -0800 John Hubbard <jhubbard@...dia.com> wrote:
> 
>> After DMA is complete, and the device and CPU caches are synchronized,
>> it's still required to mark the CPU pages as dirty, if the data was
>> coming from the device. However, this driver was just issuing a
>> bare put_page() call, without any set_page_dirty*() call.
>>
>> Fix the problem, by calling set_page_dirty_lock() if the CPU pages
>> were potentially receiving data from the device.
>>
>> Reviewed-by: Christoph Hellwig <hch@....de>
>> Acked-by: Hans Verkuil <hverkuil-cisco@...all.nl>
>> Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
>> Cc: <stable@...r.kernel.org>
> 
> What are the user-visible effects of this change?

I'll have to defer to Hans or other experts, because I merely spotted
this by reading the code.

> 
> As it's cc:stable I'd normally send this to Linus within 1-2 weeks, or
> sooner.  Please confirm that this is a standalone fix, independent of
> the rest of this series.
> 
> 

Yes, this is a stand-alone fix. Of course, as part of this series, the
put_page() gets converted to put_user_pages_dirty() in the next patch,
and that in turn gets renamed to unpin_user_pages_dirty() in a later
patch. Just so we keep that in mind when moving patches around.


thanks,
-- 
John Hubbard
NVIDIA