linux-kernel - [PATCH 3/3] misc: xilinx-sdfec: convert get_user_pages() --> pin_user

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Date:   Tue, 26 May 2020 18:26:28 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     LKML <linux-kernel@...r.kernel.org>
CC:     Souptick Joarder <jrdr.linux@...il.com>,
        John Hubbard <jhubbard@...dia.com>,
        Derek Kiernan <derek.kiernan@...inx.com>,
        Dragan Cvetic <dragan.cvetic@...inx.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michal Simek <michal.simek@...inx.com>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: [PATCH 3/3] misc: xilinx-sdfec: convert get_user_pages() --> pin_user_pages()

This code was using get_user_pages*(), in approximately a "Case 1"
scenario (Direct IO), using the categorization from [1]. That means
that it's time to convert the get_user_pages*() + put_page() calls to
pin_user_pages*() + unpin_user_pages() calls.

There is some helpful background in [2]: basically, this is a small
part of fixing a long-standing disconnect between pinning pages, and
file systems' use of those pages.

[1] Documentation/core-api/pin_user_pages.rst

[2] "Explicit pinning of user-space pages":
    https://lwn.net/Articles/807108/

Cc: Derek Kiernan <derek.kiernan@...inx.com>
Cc: Dragan Cvetic <dragan.cvetic@...inx.com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Michal Simek <michal.simek@...inx.com>
Cc: linux-arm-kernel@...ts.infradead.org
Signed-off-by: John Hubbard <jhubbard@...dia.com>
---
 drivers/misc/xilinx_sdfec.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/misc/xilinx_sdfec.c b/drivers/misc/xilinx_sdfec.c
index 7e2ee3e547f2..cda3559025d5 100644
--- a/drivers/misc/xilinx_sdfec.c
+++ b/drivers/misc/xilinx_sdfec.c
@@ -627,12 +627,11 @@ static int xsdfec_table_write(struct xsdfec_dev *xsdfec, u32 offset,
 
 	nr_pages = n;
 
-	res = get_user_pages_fast((unsigned long)src_ptr, nr_pages, 0, pages);
+	res = pin_user_pages_fast((unsigned long)src_ptr, nr_pages, 0, pages);
 	if (res < nr_pages) {
-		if (res > 0) {
-			for (i = 0; i < res; i++)
-				put_page(pages[i]);
-		}
+		if (res > 0)
+			unpin_user_pages(pages, res);
+
 		return -EINVAL;
 	}
 
@@ -646,7 +645,7 @@ static int xsdfec_table_write(struct xsdfec_dev *xsdfec, u32 offset,
 			reg++;
 		} while ((reg < len) &&
 			 ((reg * XSDFEC_REG_WIDTH_JUMP) % PAGE_SIZE));
-		put_page(pages[i]);
+		unpin_user_page(pages[i]);
 	}
 	return 0;
 }
-- 
2.26.2