linux-kernel - [PATCH 02/37] mm, frame_vector: do not use get_user_pages

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Message-Id: <20151117033514.B104D3A2@viggo.jf.intel.com>
Date:	Mon, 16 Nov 2015 19:35:14 -0800
From:	Dave Hansen <dave@...1.net>
To:	linux-kernel@...r.kernel.org
Cc:	x86@...nel.org, Dave Hansen <dave@...1.net>,
	dave.hansen@...ux.intel.com, jack@...e.cz,
	akpm@...ux-foundation.org, aarcange@...hat.com
Subject: [PATCH 02/37] mm, frame_vector: do not use get_user_pages_locked()


From: Dave Hansen <dave.hansen@...ux.intel.com>

get_user_pages_locked() appears to be for use when a caller needs
to know that its lock on mmap_sem was invalidated by the gup
call.

But, get_vaddr_frames() is not one of those users.  It
unconditionally locks the mmap_sem and unconditionally unlocks it
after the gup call.  It takes no special action and does not need
to know whether its lock was invalidated or not.

Replace get_user_pages_locked() with a vanilla get_user_pages()
and save a few lines of code.

Note that this was the *ONLY* use of get_user_pages_locked() in
the entire kernel tree.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Jan Kara <jack@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andrea Arcangeli <aarcange@...hat.com>
---

 b/mm/frame_vector.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff -puN mm/frame_vector.c~remove-get_user_pages_locked-user mm/frame_vector.c
--- a/mm/frame_vector.c~remove-get_user_pages_locked-user	2015-11-16 12:35:35.282169293 -0800
+++ b/mm/frame_vector.c	2015-11-16 12:35:35.285169429 -0800
@@ -40,7 +40,6 @@ int get_vaddr_frames(unsigned long start
 	struct vm_area_struct *vma;
 	int ret = 0;
 	int err;
-	int locked;
 
 	if (nr_frames == 0)
 		return 0;
@@ -49,7 +48,6 @@ int get_vaddr_frames(unsigned long start
 		nr_frames = vec->nr_allocated;
 
 	down_read(&mm->mmap_sem);
-	locked = 1;
 	vma = find_vma_intersection(mm, start, start + 1);
 	if (!vma) {
 		ret = -EFAULT;
@@ -58,8 +56,8 @@ int get_vaddr_frames(unsigned long start
 	if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
 		vec->got_ref = true;
 		vec->is_pfns = false;
-		ret = get_user_pages_locked(current, mm, start, nr_frames,
-			write, force, (struct page **)(vec->ptrs), &locked);
+		ret = get_user_pages(current, mm, start, nr_frames,
+			write, force, (struct page **)(vec->ptrs), NULL);
 		goto out;
 	}
 
@@ -87,8 +85,7 @@ int get_vaddr_frames(unsigned long start
 		vma = find_vma_intersection(mm, start, start + 1);
 	} while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
 out:
-	if (locked)
-		up_read(&mm->mmap_sem);
+	up_read(&mm->mmap_sem);
 	if (!ret)
 		ret = -EFAULT;
 	if (ret > 0)
_
--
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