On Fri, Jul 19, 2019 at 02:28:39PM -0700, John Hubbard wrote:
> On 7/19/19 1:02 PM, Bharath Vedartham wrote:
> > There have been issues with coordination of various subsystems using
> > get_user_pages. These issues are better described in [1].
> >
> > An implementation of tracking get_user_pages is currently underway
> > The implementation requires the use put_user_page*() variants to release
> > a reference rather than put_page(). The commit that introduced
> > put_user_pages, Commit fc1d8e7cca2daa18d2fe56b94874848adf89d7f5 ("mm:
> > introduce
> > put_user_page*(), placeholder version").
> >
> > The implementation currently simply calls put_page() within
> > put_user_page(). But in the future, it is to change to add a mechanism
> > to keep track of get_user_pages. Once a tracking mechanism is
> > implemented, we can make attempts to work on improving on coordination
> > between various subsystems using get_user_pages.
> >
> > [1] https://lwn.net/Articles/753027/
>
> Optional: I've been fussing about how to keep the change log reasonable,
> and finally came up with the following recommended template for these
> conversion patches. This would replace the text you have above, because the
> put_user_page placeholder commit has all the documentation (and then some)
> that we need:
>
>
> For pages that were retained via get_user_pages*(), release those pages
> via the new put_user_page*() routines, instead of via put_page().
>
> This is part a tree-wide conversion, as described in commit fc1d8e7cca2d
> ("mm: introduce put_user_page*(), placeholder versions").
Great then, I ll send another patch with the updated changelog.
>
> For the change itself, you will need to rebase it onto the latest
> linux.git, as it doesn't quite apply there.
>
> Testing is good if we can get it, but as far as I can tell this is
> correct, so you can also add:
>
> Reviewed-by: John Hubbard <jhubb...@nvidia.com>
Thanks!
> thanks,
> --
> John Hubbard
> NVIDIA
>
> >
> > Cc: Ira Weiny <ira.we...@intel.com>
> > Cc: John Hubbard <jhubb...@nvidia.com>
> > Cc: Jérôme Glisse <jgli...@redhat.com>
> > Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
> > Cc: Matt Sickler <matt.sick...@daktronics.com>
> > Cc: de...@driverdev.osuosl.org
> > Cc: linux-kernel@vger.kernel.org
> > Cc: linux...@kvack.org
> > Signed-off-by: Bharath Vedartham <linux.b...@gmail.com>
> > ---
> > Changes since v1
> > - Improved changelog by John's suggestion.
> > - Moved logic to dirty pages below sg_dma_unmap
> > and removed PageReserved check.
> > Changes since v2
> > - Added back PageResevered check as suggested by John Hubbard.
> >
> > The PageReserved check needs a closer look and is not worth messing
> > around with for now.
> >
> > Matt, Could you give any suggestions for testing this patch?
> >
> > If in-case, you are willing to pick this up to test. Could you
> > apply this patch to this tree
> > https://github.com/johnhubbard/linux/tree/gup_dma_core
> > and test it with your devices?
> >
> > ---
> > drivers/staging/kpc2000/kpc_dma/fileops.c | 17 ++++++-----------
> > 1 file changed, 6 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/staging/kpc2000/kpc_dma/fileops.c
> > b/drivers/staging/kpc2000/kpc_dma/fileops.c
> > index 6166587..75ad263 100644
> > --- a/drivers/staging/kpc2000/kpc_dma/fileops.c
> > +++ b/drivers/staging/kpc2000/kpc_dma/fileops.c
> > @@ -198,9 +198,7 @@ int kpc_dma_transfer(struct dev_private_data *priv,
> > struct kiocb *kcb, unsigned
> > sg_free_table(&acd->sgt);
> > err_dma_map_sg:
> > err_alloc_sg_table:
> > - for (i = 0 ; i < acd->page_count ; i++){
> > - put_page(acd->user_pages[i]);
> > - }
> > + put_user_pages(acd->user_pages, acd->page_count);
> > err_get_user_pages:
> > kfree(acd->user_pages);
> > err_alloc_userpages:
> > @@ -221,16 +219,13 @@ void transfer_complete_cb(struct aio_cb_data *acd,
> > size_t xfr_count, u32 flags)
> >
> > dev_dbg(&acd->ldev->pldev->dev, "transfer_complete_cb(acd = [%p])\n",
> > acd);
> >
> > - for (i = 0 ; i < acd->page_count ; i++){
> > - if (!PageReserved(acd->user_pages[i])){
> > - set_page_dirty(acd->user_pages[i]);
> > - }
> > - }
> > -
> > dma_unmap_sg(&acd->ldev->pldev->dev, acd->sgt.sgl, acd->sgt.nents,
> > acd->ldev->dir);
> >
> > - for (i = 0 ; i < acd->page_count ; i++){
> > - put_page(acd->user_pages[i]);
> > + for (i = 0; i < acd->page_count; i++) {
> > + if (!PageReserved(acd->user_pages[i]))
> > + put_user_pages_dirty(&acd->user_pages[i], 1);
> > + else
> > + put_user_page(acd->user_pages[i]);
> > }
> >
> > sg_free_table(&acd->sgt);
> >
