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>

1 files changed, 27 insertions, 26 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index e8dcfc7de866..4a9c2a391e28 100644
--- 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;
 }