2 files changed, 13 insertions, 0 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 84988d4ff8fb..93eb291181f7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -691,6 +691,11 @@ static bool __is_vma_write_locked(struct vm_area_struct *vma, int *mm_lock_seq)
 	return (vma->vm_lock_seq == *mm_lock_seq);
 }
 
+/*
+ * Begin writing to a VMA.
+ * Exclude concurrent readers under the per-VMA lock until the currently
+ * write-locked mmap_lock is dropped or downgraded.
+ */
 static inline void vma_start_write(struct vm_area_struct *vma)
 {
 	int mm_lock_seq;
diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index a5c63b6d7d46..8d38dcb6d044 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -73,6 +73,14 @@ static inline void mmap_assert_write_locked(struct mm_struct *mm)
 }
 
 #ifdef CONFIG_PER_VMA_LOCK
+/*
+ * Drop all currently-held per-VMA locks.
+ * This is called from the mmap_lock implementation directly before releasing
+ * a write-locked mmap_lock (or downgrading it to read-locked).
+ * This should normally NOT be called manually from other places.
+ * If you want to call this manually anyway, keep in mind that this will release
+ * *all* VMA write locks, including ones from further up the stack.
+ */
 static inline void vma_end_write_all(struct mm_struct *mm)
 {
 	mmap_assert_write_locked(mm);