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>

mm/mmap.c

@@ -1639,18 +1639,20 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
 {
 	struct vm_area_struct *vma = NULL;
 
-	if (mm) {
+	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;
+		struct rb_node *rb_node;
 
 		rb_node = mm->mm_rb.rb_node;
 		vma = NULL;
 
 		while (rb_node) {
-				struct vm_area_struct * vma_tmp;
+			struct vm_area_struct *vma_tmp;
 
 			vma_tmp = rb_entry(rb_node,
 					   struct vm_area_struct, vm_rb);
@@ -1666,7 +1668,6 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
 		if (vma)
 			mm->mmap_cache = vma;
 	}
-	}
 	return vma;
 }