linux-kernel - [PATCH 4.4 74/88] mm: remove write/force parameters from __get_user_pages

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Date:   Fri, 14 Dec 2018 13:00:48 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lorenzo Stoakes <lstoakes@...il.com>,
        Jan Kara <jack@...e.cz>, Michal Hocko <mhocko@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ben Hutchings <ben.hutchings@...ethink.co.uk>
Subject: [PATCH 4.4 74/88] mm: remove write/force parameters from __get_user_pages_locked()

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Lorenzo Stoakes <lstoakes@...il.com>

commit 859110d7497cdd0e6b21010d6f777049d676382c upstream.

This removes the redundant 'write' and 'force' parameters from
__get_user_pages_locked() to make the use of FOLL_FORCE explicit in
callers as use of this flag can result in surprising behaviour (and
hence bugs) within the mm subsystem.

Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Acked-by: Michal Hocko <mhocko@...e.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
[bwh: Backported to 4.4:
 - Drop change in get_user_pages_remote()
 - Adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@...ethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/gup.c |   37 ++++++++++++++++++++++++++-----------
 1 file changed, 26 insertions(+), 11 deletions(-)

--- a/mm/gup.c
+++ b/mm/gup.c
@@ -627,7 +627,6 @@ static __always_inline long __get_user_p
 						struct mm_struct *mm,
 						unsigned long start,
 						unsigned long nr_pages,
-						int write, int force,
 						struct page **pages,
 						struct vm_area_struct **vmas,
 						int *locked, bool notify_drop,
@@ -645,10 +644,6 @@ static __always_inline long __get_user_p
 
 	if (pages)
 		flags |= FOLL_GET;
-	if (write)
-		flags |= FOLL_WRITE;
-	if (force)
-		flags |= FOLL_FORCE;
 
 	pages_done = 0;
 	lock_dropped = false;
@@ -745,8 +740,15 @@ long get_user_pages_locked(struct task_s
 			   int write, int force, struct page **pages,
 			   int *locked)
 {
-	return __get_user_pages_locked(tsk, mm, start, nr_pages, write, force,
-				       pages, NULL, locked, true, FOLL_TOUCH);
+	unsigned int flags = FOLL_TOUCH;
+
+	if (write)
+		flags |= FOLL_WRITE;
+	if (force)
+		flags |= FOLL_FORCE;
+
+	return __get_user_pages_locked(tsk, mm, start, nr_pages,
+				       pages, NULL, locked, true, flags);
 }
 EXPORT_SYMBOL(get_user_pages_locked);
 
@@ -767,9 +769,15 @@ __always_inline long __get_user_pages_un
 {
 	long ret;
 	int locked = 1;
+
+	if (write)
+		gup_flags |= FOLL_WRITE;
+	if (force)
+		gup_flags |= FOLL_FORCE;
+
 	down_read(&mm->mmap_sem);
-	ret = __get_user_pages_locked(tsk, mm, start, nr_pages, write, force,
-				      pages, NULL, &locked, false, gup_flags);
+	ret = __get_user_pages_locked(tsk, mm, start, nr_pages, pages, NULL,
+				      &locked, false, gup_flags);
 	if (locked)
 		up_read(&mm->mmap_sem);
 	return ret;
@@ -861,8 +869,15 @@ long get_user_pages(struct task_struct *
 		unsigned long start, unsigned long nr_pages, int write,
 		int force, struct page **pages, struct vm_area_struct **vmas)
 {
-	return __get_user_pages_locked(tsk, mm, start, nr_pages, write, force,
-				       pages, vmas, NULL, false, FOLL_TOUCH);
+	unsigned int flags = FOLL_TOUCH;
+
+	if (write)
+		flags |= FOLL_WRITE;
+	if (force)
+		flags |= FOLL_FORCE;
+
+	return __get_user_pages_locked(tsk, mm, start, nr_pages,
+				       pages, vmas, NULL, false, flags);
 }
 EXPORT_SYMBOL(get_user_pages);