linux-kernel - [PATCH 1/2] mm: introduce put_user

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Message-Id: <20180709080554.21931-2-jhubbard@nvidia.com>
Date:   Mon,  9 Jul 2018 01:05:53 -0700
From:   john.hubbard@...il.com
To:     Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Christopher Lameter <cl@...ux.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Dan Williams <dan.j.williams@...el.com>,
        Jan Kara <jack@...e.cz>, Al Viro <viro@...iv.linux.org.uk>
Cc:     linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, John Hubbard <jhubbard@...dia.com>
Subject: [PATCH 1/2] mm: introduce put_user_page(), placeholder version

From: John Hubbard <jhubbard@...dia.com>

Introduces put_user_page(), which simply calls put_page().
This provides a safe way to update all get_user_pages*() callers,
so that they call put_user_page(), instead of put_page().

Also adds release_user_pages(), a drop-in replacement for
release_pages(). This is intended to be easily grep-able,
for later performance improvements, since release_user_pages
is not batched like release_pages is, and is significantly
slower.

Subsequent patches will add functionality to put_user_page().

Signed-off-by: John Hubbard <jhubbard@...dia.com>
---
 include/linux/mm.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a0fbb9ffe380..db4a211aad79 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -923,6 +923,20 @@ static inline void put_page(struct page *page)
 		__put_page(page);
 }
 
+/* Placeholder version, until all get_user_pages*() callers are updated. */
+static inline void put_user_page(struct page *page)
+{
+	put_page(page);
+}
+
+/* A drop-in replacement for release_pages(): */
+static inline void release_user_pages(struct page **pages,
+				      unsigned long npages)
+{
+	while (npages)
+		put_user_page(pages[--npages]);
+}
+
 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
 #define SECTION_IN_PAGE_FLAGS
 #endif
-- 
2.18.0