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SubjectRe: [PATCH] staging: kpc2000: Convert put_page() to put_user_page*()
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On 7/15/19 12:52 PM, Bharath Vedartham wrote:
> There have been issues with get_user_pages and filesystem writeback.
> The issues are better described in [1].
>
> The solution being proposed wants to keep track of gup_pinned pages which will allow to take furthur steps to coordinate between subsystems using gup.
>
> put_user_page() simply calls put_page inside for now. But the implementation will change once all call sites of put_page() are converted.
>
> I currently do not have the driver to test. Could I have some suggestions to test this code? The solution is currently implemented in [2] and
> it would be great if we could apply the patch on top of [2] and run some tests to check if any regressions occur.

Hi Bharath,

Process point: the above paragraph, and other meta-questions (about the patch, rather than part of the patch) should be placed either after the "---", or in a cover letter (git-send-email --cover-letter). That way, the patch itself is in a commit-able state.

One more below:

>
> [1] https://lwn.net/Articles/753027/
> [2] https://github.com/johnhubbard/linux/tree/gup_dma_core
>
> Cc: Matt Sickler <Matt.Sickler@daktronics.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Jérôme Glisse <jglisse@redhat.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: linux-mm@kvack.org
> Cc: devel@driverdev.osuosl.org
>
> Signed-off-by: Bharath Vedartham <linux.bhar@gmail.com>
> ---
> drivers/staging/kpc2000/kpc_dma/fileops.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/staging/kpc2000/kpc_dma/fileops.c b/drivers/staging/kpc2000/kpc_dma/fileops.c
> index 6166587..82c70e6 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:
> @@ -229,9 +227,7 @@ void transfer_complete_cb(struct aio_cb_data *acd, size_t xfr_count, u32 flags)
>
> 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]);
> - }
> + put_user_pages(acd->user_pages, acd->page_count);
>
> sg_free_table(&acd->sgt);
>
>

Because this is a common pattern, and because the code here doesn't likely need to set page dirty before the dma_unmap_sg call, I think the following would be better (it's untested), instead of the above diff hunk:

diff --git a/drivers/staging/kpc2000/kpc_dma/fileops.c b/drivers/staging/kpc2000/kpc_dma/fileops.c
index 48ca88bc6b0b..d486f9866449 100644
--- a/drivers/staging/kpc2000/kpc_dma/fileops.c
+++ b/drivers/staging/kpc2000/kpc_dma/fileops.c
@@ -211,16 +211,13 @@ void transfer_complete_cb(struct aio_cb_data *acd, size_t xfr_count, u32 flags)
BUG_ON(acd->ldev == NULL);
BUG_ON(acd->ldev->pldev == NULL);

- 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]);
+ 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);
Assuming that you make those two changes, you can add:

Reviewed-by: John Hubbard <jhubbard@nvidia.com>


thanks,
--
John Hubbard
NVIDIA

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