linux-kernel - [PATCH v3] staging: kpc2000: Convert put_page to put_user

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Date:   Sat, 20 Jul 2019 01:32:35 +0530
From:   Bharath Vedartham <linux.bhar@...il.com>
To:     jhubbard@...dia.com, ira.weiny@...el.com, jglisse@...hat.com,
        gregkh@...uxfoundation.org, Matt.Sickler@...tronics.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        devel@...verdev.osuosl.org
Subject: [PATCH v3] staging: kpc2000: Convert put_page to put_user_page*()

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/

Cc: Ira Weiny <ira.weiny@...el.com>
Cc: John Hubbard <jhubbard@...dia.com>
Cc: Jérôme Glisse <jglisse@...hat.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Matt Sickler <Matt.Sickler@...tronics.com>
Cc: devel@...verdev.osuosl.org 
Cc: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org
Signed-off-by: Bharath Vedartham <linux.bhar@...il.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);
-- 
2.7.4