Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   John Hubbard <jhubbard@nvidia.com>
To:     LKML <linux-kernel@vger.kernel.org>
CC:     John Hubbard <jhubbard@nvidia.com>,
        "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, <netdev@vger.kernel.org>,
        <linux-rdma@vger.kernel.org>, <rds-devel@oss.oracle.com>
Subject: [PATCH] rds: convert get_user_pages() --> pin_user_pages()
Date:   Sat, 16 May 2020 18:23:36 -0700
Message-ID: <20200517012336.382624-1-jhubbard@nvidia.com>
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

This code was using get_user_pages_fast(), in a "Case 2" scenario
(DMA/RDMA), using the categorization from [1]. That means that it's
time to convert the get_user_pages_fast() + put_page() calls to
pin_user_pages_fast() + 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: David S. Miller <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org
Cc: linux-rdma@vger.kernel.org
Cc: rds-devel@oss.oracle.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 net/rds/info.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/rds/info.c b/net/rds/info.c
index 03f6fd56d237..e1d63563e81c 100644
--- a/net/rds/info.c
+++ b/net/rds/info.c
@@ -162,7 +162,6 @@ int rds_info_getsockopt(struct socket *sock, int optnam=
e, char __user *optval,
 	struct rds_info_lengths lens;
 	unsigned long nr_pages =3D 0;
 	unsigned long start;
-	unsigned long i;
 	rds_info_func func;
 	struct page **pages =3D NULL;
 	int ret;
@@ -193,7 +192,7 @@ int rds_info_getsockopt(struct socket *sock, int optnam=
e, char __user *optval,
 		ret =3D -ENOMEM;
 		goto out;
 	}
-	ret =3D get_user_pages_fast(start, nr_pages, FOLL_WRITE, pages);
+	ret =3D pin_user_pages_fast(start, nr_pages, FOLL_WRITE, pages);
 	if (ret !=3D nr_pages) {
 		if (ret > 0)
 			nr_pages =3D ret;
@@ -235,8 +234,7 @@ int rds_info_getsockopt(struct socket *sock, int optnam=
e, char __user *optval,
 		ret =3D -EFAULT;
=20
 out:
-	for (i =3D 0; pages && i < nr_pages; i++)
-		put_page(pages[i]);
+	unpin_user_pages(pages, nr_pages);
 	kfree(pages);
=20
 	return ret;

base-commit: 3d1c1e5931ce45b3a3f309385bbc00c78e9951c6
--=20
2.26.2