VM: add "vm_munmap()" helper function

Like the vm_brk() function, this is the same as "do_munmap()", except it
does the VM locking for the caller.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/mm.h b/include/linux/mm.h
index bfee4ad..cb61950 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1417,6 +1417,7 @@
 
 /* These take the mm semaphore themselves */
 extern unsigned long vm_brk(unsigned long, unsigned long);
+extern int vm_munmap(struct mm_struct *, unsigned long, size_t);
 
 /* truncate.c */
 extern void truncate_inode_pages(struct address_space *, loff_t);