linux-kernel - [PATCH v2] staging: kpc2000: Convert put_page() to put_user

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Message-ID: <20190715214926.GA29665@bharath12345-Inspiron-5559>
Date:   Tue, 16 Jul 2019 03:19:26 +0530
From:   Bharath Vedartham <linux.bhar@...il.com>
To:     Matt.Sickler@...tronics.com, gregkh@...uxfoundation.org,
        jglisse@...hat.com, ira.weiny@...el.com, jhubbard@...dia.com
Cc:     linux-mm@...ck.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
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@...tronics.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jérôme Glisse <jglisse@...hat.com>
Cc: Ira Weiny <ira.weiny@...el.com>
Cc: John Hubbard <jhubbard@...dia.com>
Cc: linux-mm@...ck.org
Cc: devel@...verdev.osuosl.org

Reviewed-by: John Hubbard <jhubbard@...dia.com>
Signed-off-by: Bharath Vedartham <linux.bhar@...il.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