Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 16 Jul 2019 01:22:48 +0530
From:   Bharath Vedartham <linux.bhar@gmail.com>
To:     ira.weiny@intel.com, jhubbard@nvidia.com,
        gregkh@linuxfoundation.org, Matt.Sickler@daktronics.com,
        jglisse@redhat.com
Cc:     devel@driverdev.osuosl.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] staging: kpc2000: Convert put_page() to put_user_page*()
Message-ID: <20190715195248.GA22495@bharath12345-Inspiron-5559>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.

[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: J?r?me 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);
 	
-- 
1.8.3.1