linux-kernel - [PATCH 4.14 11/95] v4l2: disable filesystem-dax mapping support

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Date:   Mon,  4 Dec 2017 16:59:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dan Williams <dan.j.williams@...el.com>,
        Jan Kara <jack@...e.cz>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Doug Ledford <dledford@...hat.com>,
        Hal Rosenstock <hal.rosenstock@...il.com>,
        Inki Dae <inki.dae@...sung.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Jeff Moyer <jmoyer@...hat.com>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Mel Gorman <mgorman@...e.de>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Sean Hefty <sean.hefty@...el.com>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.14 11/95] v4l2: disable filesystem-dax mapping support

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Williams <dan.j.williams@...el.com>

commit b70131de648c2b997d22f4653934438013f407a1 upstream.

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.

Link: http://lkml.kernel.org/r/151068940499.7446.12846708245365671207.stgit@dwillia2-desk3.amr.corp.intel.com
Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Reported-by: Jan Kara <jack@...e.cz>
Reviewed-by: Jan Kara <jack@...e.cz>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: Christoph Hellwig <hch@....de>
Cc: Doug Ledford <dledford@...hat.com>
Cc: Hal Rosenstock <hal.rosenstock@...il.com>
Cc: Inki Dae <inki.dae@...sung.com>
Cc: Jason Gunthorpe <jgg@...lanox.com>
Cc: Jeff Moyer <jmoyer@...hat.com>
Cc: Joonyoung Shim <jy0922.shim@...sung.com>
Cc: Kyungmin Park <kyungmin.park@...sung.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc: Sean Hefty <sean.hefty@...el.com>
Cc: Seung-Woo Kim <sw0312.kim@...sung.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/media/v4l2-core/videobuf-dma-sg.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- 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
 	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;