From patchwork Tue Nov 14 19:56:45 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dan Williams X-Patchwork-Id: 45441 Received: from vger.kernel.org ([209.132.180.67]) by www.linuxtv.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eEhXM-0001ZU-2Y; Tue, 14 Nov 2017 20:10:24 +0000 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755413AbdKNUKU (ORCPT + 1 other); Tue, 14 Nov 2017 15:10:20 -0500 Received: from mga06.intel.com ([134.134.136.31]:24453 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756315AbdKNUFA (ORCPT ); Tue, 14 Nov 2017 15:05:00 -0500 Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Nov 2017 12:04:59 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.44,396,1505804400"; d="scan'208";a="7650913" Received: from dwillia2-desk3.jf.intel.com (HELO dwillia2-desk3.amr.corp.intel.com) ([10.54.39.16]) by orsmga002.jf.intel.com with ESMTP; 14 Nov 2017 12:04:59 -0800 Subject: [PATCH v2 3/4] [media] v4l2: disable filesystem-dax mapping support From: Dan Williams To: akpm@linux-foundation.org Cc: 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 Date: Tue, 14 Nov 2017 11:56:45 -0800 Message-ID: <151068940499.7446.12846708245365671207.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <151068938905.7446.12333914805308312313.stgit@dwillia2-desk3.amr.corp.intel.com> References: <151068938905.7446.12333914805308312313.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: StGit/0.17.1-9-g687f MIME-Version: 1.0 Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org 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 Reviewed-by: Jan Kara --- 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;