From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933540AbdKGId5 (ORCPT ); Tue, 7 Nov 2017 03:33:57 -0500 Received: from osg.samsung.com ([64.30.133.232]:59814 "EHLO osg.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932811AbdKGIdz (ORCPT ); Tue, 7 Nov 2017 03:33:55 -0500 Date: Tue, 7 Nov 2017 06:33:45 -0200 From: Mauro Carvalho Chehab To: Dan Williams Cc: akpm@linux-foundation.org, Jan Kara , linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux-mm@kvack.org, Mauro Carvalho Chehab , linux-media@vger.kernel.org Subject: Re: [PATCH 3/3] [media] v4l2: disable filesystem-dax mapping support Message-ID: <20171107063345.22626a5d@vento.lan> In-Reply-To: <151001624873.16354.2551756846133945335.stgit@dwillia2-desk3.amr.corp.intel.com> References: <151001623063.16354.14661493921524115663.stgit@dwillia2-desk3.amr.corp.intel.com> <151001624873.16354.2551756846133945335.stgit@dwillia2-desk3.amr.corp.intel.com> Organization: Samsung X-Mailer: Claws Mail 3.15.1-dirty (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Mon, 06 Nov 2017 16:57:28 -0800 Dan Williams escreveu: > 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. Not sure if I understand this your comment here... what happens if FS_DAX is enabled? The new err = get_user_pages_longterm() would cause DMA allocation to fail? If so, that doesn't sound right. Instead, mm should somehow mark this mapping to be out of FS_DAX control range. Also, it is not only videobuf-dma-sg.c that does long lived DMA mappings. VB2 also does that (and videobuf-vmalloc). Regards, Mauro > > 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; > Thanks, Mauro From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 7 Nov 2017 06:33:45 -0200 From: Mauro Carvalho Chehab To: Dan Williams Cc: akpm@linux-foundation.org, Jan Kara , linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux-mm@kvack.org, Mauro Carvalho Chehab , linux-media@vger.kernel.org Subject: Re: [PATCH 3/3] [media] v4l2: disable filesystem-dax mapping support Message-ID: <20171107063345.22626a5d@vento.lan> In-Reply-To: <151001624873.16354.2551756846133945335.stgit@dwillia2-desk3.amr.corp.intel.com> References: <151001623063.16354.14661493921524115663.stgit@dwillia2-desk3.amr.corp.intel.com> <151001624873.16354.2551756846133945335.stgit@dwillia2-desk3.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: Em Mon, 06 Nov 2017 16:57:28 -0800 Dan Williams escreveu: > 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. Not sure if I understand this your comment here... what happens if FS_DAX is enabled? The new err = get_user_pages_longterm() would cause DMA allocation to fail? If so, that doesn't sound right. Instead, mm should somehow mark this mapping to be out of FS_DAX control range. Also, it is not only videobuf-dma-sg.c that does long lived DMA mappings. VB2 also does that (and videobuf-vmalloc). Regards, Mauro > > 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; > Thanks, Mauro -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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