linux-kernel - Re: [PATCH v2 13/18] media/v4l2-core: pin_longterm_pages (FOLL_PIN) and put_user

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Message-ID: <6d21391e-01c4-0605-0d0d-15f574cc3ed4@xs4all.nl>
Date:   Sun, 10 Nov 2019 11:11:45 +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 13/18] media/v4l2-core: pin_longterm_pages (FOLL_PIN)
 and put_user_page() conversion

On 11/3/19 10:18 PM, John Hubbard wrote:
> 1. Change v4l2 from get_user_pages(FOLL_LONGTERM), to
> pin_longterm_pages(), which sets both FOLL_LONGTERM and FOLL_PIN.
> 
> 2. Because all FOLL_PIN-acquired pages must be released via
> put_user_page(), also convert the put_page() call over to
> put_user_pages_dirty_lock().
> 
> Reviewed-by: Ira Weiny <ira.weiny@...el.com>
> 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 | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c
> index 28262190c3ab..9b9c5b37bf59 100644
> --- a/drivers/media/v4l2-core/videobuf-dma-sg.c
> +++ b/drivers/media/v4l2-core/videobuf-dma-sg.c
> @@ -183,12 +183,12 @@ static int videobuf_dma_init_user_locked(struct videobuf_dmabuf *dma,
>  	dprintk(1, "init user [0x%lx+0x%lx => %d pages]\n",
>  		data, size, dma->nr_pages);
>  
> -	err = get_user_pages(data & PAGE_MASK, dma->nr_pages,
> -			     flags | FOLL_LONGTERM, dma->pages, NULL);
> +	err = pin_longterm_pages(data & PAGE_MASK, dma->nr_pages,
> +				 flags, dma->pages, NULL);
>  
>  	if (err != dma->nr_pages) {
>  		dma->nr_pages = (err >= 0) ? err : 0;
> -		dprintk(1, "get_user_pages: err=%d [%d]\n", err,
> +		dprintk(1, "pin_longterm_pages: err=%d [%d]\n", err,
>  			dma->nr_pages);
>  		return err < 0 ? err : -EINVAL;
>  	}
> @@ -349,11 +349,8 @@ int videobuf_dma_free(struct videobuf_dmabuf *dma)
>  	BUG_ON(dma->sglen);
>  
>  	if (dma->pages) {
> -		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]);
> -		}
> +		put_user_pages_dirty_lock(dma->pages, dma->nr_pages,
> +					  dma->direction == DMA_FROM_DEVICE);
>  		kfree(dma->pages);
>  		dma->pages = NULL;
>  	}
>