From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935091AbdKGBFz (ORCPT ); Mon, 6 Nov 2017 20:05:55 -0500 Received: from mga07.intel.com ([134.134.136.100]:41667 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935062AbdKGBFn (ORCPT ); Mon, 6 Nov 2017 20:05:43 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.44,355,1505804400"; d="scan'208";a="4246191" Subject: [PATCH 3/3] [media] v4l2: disable filesystem-dax mapping support From: Dan Williams To: akpm@linux-foundation.org Cc: Jan Kara , linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux-mm@kvack.org, Mauro Carvalho Chehab , linux-media@vger.kernel.org Date: Mon, 06 Nov 2017 16:57:28 -0800 Message-ID: <151001624873.16354.2551756846133945335.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <151001623063.16354.14661493921524115663.stgit@dwillia2-desk3.amr.corp.intel.com> References: <151001623063.16354.14661493921524115663.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: StGit/0.17.1-9-g687f MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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: Signed-off-by: Dan Williams --- 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; From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: [PATCH 3/3] [media] v4l2: disable filesystem-dax mapping support From: Dan Williams To: akpm@linux-foundation.org Cc: Jan Kara , linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux-mm@kvack.org, Mauro Carvalho Chehab , linux-media@vger.kernel.org Date: Mon, 06 Nov 2017 16:57:28 -0800 Message-ID: <151001624873.16354.2551756846133945335.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <151001623063.16354.14661493921524115663.stgit@dwillia2-desk3.amr.corp.intel.com> References: <151001623063.16354.14661493921524115663.stgit@dwillia2-desk3.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: 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: Signed-off-by: Dan Williams --- 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; -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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