linux-kernel - Re: [PATCH v2 04/18] media/v4l2-core: set pages dirty upon releasing DMA buffers

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Message-ID: <4b2337f6-102d-ae9d-e690-4331d77660c4@xs4all.nl>
Date:   Sun, 10 Nov 2019 11:10:10 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     John Hubbard <jhubbard@...dia.com>,
        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>
Subject: Re: [PATCH v2 04/18] media/v4l2-core: set pages dirty upon releasing
 DMA buffers

On 11/3/19 10:17 PM, John Hubbard 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.
> 
> Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
> Signed-off-by: John Hubbard <jhubbard@...dia.com>

Acked-by: Hans Verkuil <hverkuil-cisco@...all.nl>

Looks good, thanks!

	Hans

> ---
>  drivers/media/v4l2-core/videobuf-dma-sg.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c
> index 66a6c6c236a7..28262190c3ab 100644
> --- a/drivers/media/v4l2-core/videobuf-dma-sg.c
> +++ b/drivers/media/v4l2-core/videobuf-dma-sg.c
> @@ -349,8 +349,11 @@ int videobuf_dma_free(struct videobuf_dmabuf *dma)
>  	BUG_ON(dma->sglen);
>  
>  	if (dma->pages) {
> -		for (i = 0; i < dma->nr_pages; i++)
> +		for (i = 0; i < dma->nr_pages; i++) {
> +			if (dma->direction == DMA_FROM_DEVICE)
> +				set_page_dirty_lock(dma->pages[i]);
>  			put_page(dma->pages[i]);
> +		}
>  		kfree(dma->pages);
>  		dma->pages = NULL;
>  	}
>