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.st...@dwillia2-desk3.amr.corp.intel.com
Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
Reported-by: Jan Kara <j...@suse.cz>
Reviewed-by: Jan Kara <j...@suse.cz>
Cc: Mauro Carvalho Chehab <mche...@kernel.org>
Cc: Christoph Hellwig <h...@lst.de>
Cc: Doug Ledford <dledf...@redhat.com>
Cc: Hal Rosenstock <hal.rosenst...@gmail.com>
Cc: Inki Dae <inki....@samsung.com>
Cc: Jason Gunthorpe <j...@mellanox.com>
Cc: Jeff Moyer <jmo...@redhat.com>
Cc: Joonyoung Shim <jy0922.s...@samsung.com>
Cc: Kyungmin Park <kyungmin.p...@samsung.com>
Cc: Mel Gorman <mgor...@suse.de>
Cc: Ross Zwisler <ross.zwis...@linux.intel.com>
Cc: Sean Hefty <sean.he...@intel.com>
Cc: Seung-Woo Kim <sw0312....@samsung.com>
Cc: Vlastimil Babka <vba...@suse.cz>
Cc: <sta...@vger.kernel.org>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
---
 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 1db0af6c7f94..b6189a4958c5 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;

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