| Message ID | 151068940499.7446.12846708245365671207.stgit@dwillia2-desk3.amr.corp.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue 14-11-17 11:56:45, Dan Williams wrote: > 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 <jack@suse.cz> > Cc: Mauro Carvalho Chehab <mchehab@kernel.org> > Cc: linux-media@vger.kernel.org > Cc: <stable@vger.kernel.org> > Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") > Signed-off-by: Dan Williams <dan.j.williams@intel.com> Looks good to me. You can add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > 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; >
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;
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 <jack@suse.cz> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: linux-media@vger.kernel.org Cc: <stable@vger.kernel.org> Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") Signed-off-by: Dan Williams <dan.j.williams@intel.com> --- drivers/media/v4l2-core/videobuf-dma-sg.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)