mm: for !CONFIG_PER_VMA_LOCK equate write lock assertion for vma and mmap

When CONFIG_PER_VMA_LOCK=n, vma_assert_write_locked() should be equivalent
to mmap_assert_write_locked().

Link: https://lkml.kernel.org/r/20230804152724.3090321-3-surenb@google.comSuggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -738,7 +738,8 @@ static inline bool vma_start_read(struct vm_area_struct *vma)
 		{ return false; }
 static inline void vma_end_read(struct vm_area_struct *vma) {}
 static inline void vma_start_write(struct vm_area_struct *vma) {}
-static inline void vma_assert_write_locked(struct vm_area_struct *vma) {}
+static inline void vma_assert_write_locked(struct vm_area_struct *vma)
+		{ mmap_assert_write_locked(vma->vm_mm); }
 static inline void vma_mark_detached(struct vm_area_struct *vma,
 				     bool detached) {}