mm/mmap.c: find_vma(): remove unnecessary if(mm) check

The "if (mm)" check is not required in find_vma, as the kernel code
calls find_vma only when it is absolutely sure that the mm_struct arg to
it is non-NULL.

Remove the if(mm) check and adding the a WARN_ONCE(!mm) for now.  This
will serve the purpose of mandating that the execution
context(user-mode/kernel-mode) be known before find_vma is called.  Also
fixed 2 checkpatch.pl errors in the declaration of the rb_node and
vma_tmp local variables.

I was browsing through the internet and read a discussion at
https://lkml.org/lkml/2012/3/27/342 which discusses removal of the
validation check within find_vma.  Since no-one responded, I decided to
send this patch with Andrew's suggestions.

[akpm@linux-foundation.org: add remove-me comment]
Signed-off-by: Rajman Mekaco <rajman.mekaco@gmail.com>
Cc: Kautuk Consul <consul.kautuk@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index e8dcfc7..4a9c2a3 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1639,33 +1639,34 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
 {
        struct vm_area_struct *vma = NULL;
 
-       if (mm) {
-               /* Check the cache first. */
-               /* (Cache hit rate is typically around 35%.) */
-               vma = mm->mmap_cache;
-               if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) {
-                       struct rb_node * rb_node;
-
-                       rb_node = mm->mm_rb.rb_node;
-                       vma = NULL;
-
-                       while (rb_node) {
-                               struct vm_area_struct * vma_tmp;
-
-                               vma_tmp = rb_entry(rb_node,
-                                               struct vm_area_struct, vm_rb);
-
-                               if (vma_tmp->vm_end > addr) {
-                                       vma = vma_tmp;
-                                       if (vma_tmp->vm_start <= addr)
-                                               break;
-                                       rb_node = rb_node->rb_left;
-                               } else
-                                       rb_node = rb_node->rb_right;
-                       }
-                       if (vma)
-                               mm->mmap_cache = vma;
+       if (WARN_ON_ONCE(!mm))          /* Remove this in linux-3.6 */
+               return NULL;
+
+       /* Check the cache first. */
+       /* (Cache hit rate is typically around 35%.) */
+       vma = mm->mmap_cache;
+       if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) {
+               struct rb_node *rb_node;
+
+               rb_node = mm->mm_rb.rb_node;
+               vma = NULL;
+
+               while (rb_node) {
+                       struct vm_area_struct *vma_tmp;
+
+                       vma_tmp = rb_entry(rb_node,
+                                          struct vm_area_struct, vm_rb);
+
+                       if (vma_tmp->vm_end > addr) {
+                               vma = vma_tmp;
+                               if (vma_tmp->vm_start <= addr)
+                                       break;
+                               rb_node = rb_node->rb_left;
+                       } else
+                               rb_node = rb_node->rb_right;
                }
+               if (vma)
+                       mm->mmap_cache = vma;
        }
        return vma;
 }