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Subject[PATCH v2] staging: kpc2000: Convert put_page() to put_user_page*()
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.

[1] https://lwn.net/Articles/753027/

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

Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Bharath Vedartham <linux.bhar@gmail.com>
---
Changes since v1
- Added John's reviewed-by tag
- Moved para talking about testing below
the '---'
- Moved logic of set_page_diry below dma_unmap_sg
as per John's suggestion

I currently do not have the driver to test. Could I have some
suggestions to test this code? The solution is currently implemented
in https://github.com/johnhubbard/linux/tree/gup_dma_core and it would be great
if we could apply the patch on top of the repo and run some
tests to check if any regressions occur.
---
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 48ca88b..3d1a00a 100644
--- a/drivers/staging/kpc2000/kpc_dma/fileops.c
+++ b/drivers/staging/kpc2000/kpc_dma/fileops.c
@@ -190,9 +190,7 @@ static int kpc_dma_transfer(struct dev_private_data *priv,
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:
@@ -211,16 +209,13 @@ 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]);
+ 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);
--
2.7.4
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