mm/mmap.c: use mmap_assert_write_locked() instead of open coding it

In case the lock is actually not held at this point.

Link: https://lkml.kernel.org/r/5827758.TJ1SttVevJ@mobilepool36.emlix.com
Signed-off-by: Rolf Eike Beer <eb@emlix.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmap.c

@@ -3553,7 +3553,7 @@ int mm_take_all_locks(struct mm_struct *mm)
 	struct vm_area_struct *vma;
 	struct anon_vma_chain *avc;
 
-	BUG_ON(mmap_read_trylock(mm));
+	mmap_assert_write_locked(mm);
 
 	mutex_lock(&mm_all_locks_mutex);
 
@@ -3633,7 +3633,7 @@ void mm_drop_all_locks(struct mm_struct *mm)
 	struct vm_area_struct *vma;
 	struct anon_vma_chain *avc;
 
-	BUG_ON(mmap_read_trylock(mm));
+	mmap_assert_write_locked(mm);
 	BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));
 
 	for (vma = mm->mmap; vma; vma = vma->vm_next) {