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

Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
Signed-off-by: Dan Williams <>
Reported-by: Jan Kara <>
Reviewed-by: Jan Kara <>
Cc: Mauro Carvalho Chehab <>
Cc: Christoph Hellwig <>
Cc: Doug Ledford <>
Cc: Hal Rosenstock <>
Cc: Inki Dae <>
Cc: Jason Gunthorpe <>
Cc: Jeff Moyer <>
Cc: Joonyoung Shim <>
Cc: Kyungmin Park <>
Cc: Mel Gorman <>
Cc: Ross Zwisler <>
Cc: Sean Hefty <>
Cc: Seung-Woo Kim <>
Cc: Vlastimil Babka <>
Cc: <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
 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 
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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