ksm: first tidy up madvise_vma()

madvise.c has several levels of switch statements, what to do in which?
Move MADV_DOFORK code down from madvise_vma() to madvise_behavior(), so
madvise_vma() can be a simple router, to madvise_behavior() by default.

vma->vm_flags is an unsigned long so use the same type for new_flags.  Add
missing comment lines to describe MADV_DONTFORK and MADV_DOFORK.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 26 deletions

diff --git a/mm/madvise.c b/mm/madvise.c
index 76eb4193acdd..66c31264f062 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -41,7 +41,7 @@ static long madvise_behavior(struct vm_area_struct * vma,
         struct mm_struct * mm = vma->vm_mm;
         int error = 0;
         pgoff_t pgoff;
-        int new_flags = vma->vm_flags;
+        unsigned long new_flags = vma->vm_flags;
 
         switch (behavior) {
         case MADV_NORMAL:
@@ -57,6 +57,10 @@ static long madvise_behavior(struct vm_area_struct * vma,
                 new_flags |= VM_DONTCOPY;
                 break;
         case MADV_DOFORK:
+                if (vma->vm_flags & VM_IO) {
+                        error = -EINVAL;
+                        goto out;
+                }
                 new_flags &= ~VM_DONTCOPY;
                 break;
         }
@@ -211,37 +215,16 @@ static long
 madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
                 unsigned long start, unsigned long end, int behavior)
 {
-        long error;
-
         switch (behavior) {
-        case MADV_DOFORK:
-                if (vma->vm_flags & VM_IO) {
-                        error = -EINVAL;
-                        break;
-                }
-        case MADV_DONTFORK:
-        case MADV_NORMAL:
-        case MADV_SEQUENTIAL:
-        case MADV_RANDOM:
-                error = madvise_behavior(vma, prev, start, end, behavior);
-                break;
         case MADV_REMOVE:
-                error = madvise_remove(vma, prev, start, end);
-                break;
-
+                return madvise_remove(vma, prev, start, end);
         case MADV_WILLNEED:
-                error = madvise_willneed(vma, prev, start, end);
-                break;
-
+                return madvise_willneed(vma, prev, start, end);
         case MADV_DONTNEED:
-                error = madvise_dontneed(vma, prev, start, end);
-                break;
-
+                return madvise_dontneed(vma, prev, start, end);
         default:
-                BUG();
-                break;
+                return madvise_behavior(vma, prev, start, end, behavior);
         }
-        return error;
 }
 
 static int
@@ -262,6 +245,7 @@ madvise_behavior_valid(int behavior)
                 return 0;
         }
 }
+
 /*
  * The madvise(2) system call.
  *
@@ -286,6 +270,9 @@ madvise_behavior_valid(int behavior)
  *              so the kernel can free resources associated with it.
  *  MADV_REMOVE - the application wants to free up the given range of
  *              pages and associated backing store.
+ *  MADV_DONTFORK - omit this area from child's address space when forking:
+ *              typically, to avoid COWing pages pinned by get_user_pages().
+ *  MADV_DOFORK - cancel MADV_DONTFORK: no longer omit this area when forking.
  *
  * return values:
  *  zero    - success