From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753430AbdK0QR0 (ORCPT ); Mon, 27 Nov 2017 11:17:26 -0500 Received: from mx2.suse.de ([195.135.220.15]:38110 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753363AbdK0QRX (ORCPT ); Mon, 27 Nov 2017 11:17:23 -0500 Date: Mon, 27 Nov 2017 17:17:21 +0100 From: Jan Kara To: Dan Williams Cc: akpm@linux-foundation.org, Jan Kara , linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux-mm@kvack.org, Mauro Carvalho Chehab , linux-media@vger.kernel.org Subject: Re: [PATCH v2 3/4] [media] v4l2: disable filesystem-dax mapping support Message-ID: <20171127161721.GF5977@quack2.suse.cz> References: <151068938905.7446.12333914805308312313.stgit@dwillia2-desk3.amr.corp.intel.com> <151068940499.7446.12846708245365671207.stgit@dwillia2-desk3.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <151068940499.7446.12846708245365671207.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 14-11-17 11:56:45, Dan Williams wrote: > V4L2 memory registrations are incompatible with filesystem-dax that > needs the ability to revoke dma access to a mapping at will, or > otherwise allow the kernel to wait for completion of DMA. The > filesystem-dax implementation breaks the traditional solution of > truncate of active file backed mappings since there is no page-cache > page we can orphan to sustain ongoing DMA. > > If v4l2 wants to support long lived DMA mappings it needs to arrange to > hold a file lease or use some other mechanism so that the kernel can > coordinate revoking DMA access when the filesystem needs to truncate > mappings. > > Reported-by: Jan Kara > Cc: Mauro Carvalho Chehab > Cc: linux-media@vger.kernel.org > Cc: > Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") > Signed-off-by: Dan Williams Looks good to me. You can add: Reviewed-by: Jan Kara Honza > --- > drivers/media/v4l2-core/videobuf-dma-sg.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/media/v4l2-core/videobuf-dma-sg.c b/drivers/media/v4l2-core/videobuf-dma-sg.c > index 0b5c43f7e020..f412429cf5ba 100644 > --- a/drivers/media/v4l2-core/videobuf-dma-sg.c > +++ b/drivers/media/v4l2-core/videobuf-dma-sg.c > @@ -185,12 +185,13 @@ 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, > + err = get_user_pages_longterm(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, dma->nr_pages); > + dprintk(1, "get_user_pages_longterm: err=%d [%d]\n", err, > + dma->nr_pages); > return err < 0 ? err : -EINVAL; > } > return 0; > -- Jan Kara SUSE Labs, CR