net: explain the lockdep annotations for dev_uc_unsync()

The lockdep annotations for dev_uc_unsync() and dev_mc_unsync()
are not easy to understand, so add some comments to explain
why they are correct.

Similar for the rest netif_addr_lock_bh() cases, they don't
need nested version.

Cc: Taehee Yoo <ap420073@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev_addr_lists.c b/net/core/dev_addr_lists.c
index 6393ba930097b49b26a70cf01b657da08514f552..54cd568e7c2f51bdc0da38d267f4276b6d76804e 100644 (file)
--- a/net/core/dev_addr_lists.c
+++ b/net/core/dev_addr_lists.c
@@ -690,6 +690,15 @@ void dev_uc_unsync(struct net_device *to, struct net_device *from)
        if (to->addr_len != from->addr_len)
                return;
 
+       /* netif_addr_lock_bh() uses lockdep subclass 0, this is okay for two
+        * reasons:
+        * 1) This is always called without any addr_list_lock, so as the
+        *    outermost one here, it must be 0.
+        * 2) This is called by some callers after unlinking the upper device,
+        *    so the dev->lower_level becomes 1 again.
+        * Therefore, the subclass for 'from' is 0, for 'to' is either 1 or
+        * larger.
+        */
        netif_addr_lock_bh(from);
        netif_addr_lock_nested(to);
        __hw_addr_unsync(&to->uc, &from->uc, to->addr_len);
@@ -911,6 +920,7 @@ void dev_mc_unsync(struct net_device *to, struct net_device *from)
        if (to->addr_len != from->addr_len)
                return;
 
+       /* See the above comments inside dev_uc_unsync(). */
        netif_addr_lock_bh(from);
        netif_addr_lock_nested(to);
        __hw_addr_unsync(&to->mc, &from->mc, to->addr_len);