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

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Date:   Tue, 16 Jul 2019 01:22:48 +0530
From:   Bharath Vedartham <linux.bhar@...il.com>
To:     ira.weiny@...el.com, jhubbard@...dia.com,
        gregkh@...uxfoundation.org, Matt.Sickler@...tronics.com,
        jglisse@...hat.com
Cc:     devel@...verdev.osuosl.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] 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.

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@...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

Signed-off-by: Bharath Vedartham <linux.bhar@...il.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