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>

mm/mmap.c

diff --git a/mm/mmap.c b/mm/mmap.c
index df51891..4af45f5 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2107,20 +2107,23 @@
 
 	return 0;
 }
-
 EXPORT_SYMBOL(do_munmap);
 
+int vm_munmap(struct mm_struct *mm, unsigned long start, size_t len)
+{
+	int ret;
+
+	down_write(&mm->mmap_sem);
+	ret = do_munmap(mm, start, len);
+	up_write(&mm->mmap_sem);
+	return ret;
+}
+EXPORT_SYMBOL(vm_munmap);
+
 SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
 {
-	int ret;
-	struct mm_struct *mm = current->mm;
-
 	profile_munmap(addr);
-
-	down_write(&mm->mmap_sem);
-	ret = do_munmap(mm, addr, len);
-	up_write(&mm->mmap_sem);
-	return ret;
+	return vm_munmap(current->mm, addr, len);
 }
 
 static inline void verify_mm_writelocked(struct mm_struct *mm)

mm/nommu.c

diff --git a/mm/nommu.c b/mm/nommu.c
index 6341933..11a69b2 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1709,16 +1709,21 @@
 }
 EXPORT_SYMBOL(do_munmap);
 
-SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
+int vm_munmap(struct mm_struct *mm, unsigned long addr, size_t len)
 {
 	int ret;
-	struct mm_struct *mm = current->mm;
 
 	down_write(&mm->mmap_sem);
 	ret = do_munmap(mm, addr, len);
 	up_write(&mm->mmap_sem);
 	return ret;
 }
+EXPORT_SYMBOL(vm_munmap);
+
+SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
+{
+	return vm_munmap(current->mm, addr, len);
+}
 
 /*
  * release all the mappings made in a process's VM space