fsnotify: Clarify connector assignment in fsnotify_add_mark_list()

Add a comment explaining why WRITE_ONCE() is enough when setting
mark->connector which can get dereferenced by RCU protected readers.

Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index 22acb0a79b53..b251105f646f 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -619,6 +619,11 @@ restart:
         /* mark should be the last entry.  last is the current last entry */
         hlist_add_behind_rcu(&mark->obj_list, &last->obj_list);
 added:
+        /*
+         * Since connector is attached to object using cmpxchg() we are
+         * guaranteed that connector initialization is fully visible by anyone
+         * seeing mark->connector set.
+         */
         WRITE_ONCE(mark->connector, conn);
 out_err:
         spin_unlock(&conn->lock);