rtnetlink: Protect link_ops by mutex.

rtnl_link_unregister() holds RTNL and calls synchronize_srcu(),
but rtnl_newlink() will acquire SRCU frist and then RTNL.

Then, we need to unlink ops and call synchronize_srcu() outside
of RTNL to avoid the deadlock.

   rtnl_link_unregister()       rtnl_newlink()
   ----                         ----
   lock(rtnl_mutex);
                                lock(&ops->srcu);
                                lock(rtnl_mutex);
   sync(&ops->srcu);

Let's move as such and add a mutex to protect link_ops.

Now, link_ops is protected by its dedicated mutex and
rtnl_link_register() no longer needs to hold RTNL.

While at it, we move the initialisation of ops->dellink and
ops->srcu out of the mutex scope.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20241108004823.29419-3-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/net/rtnetlink.h b/include/net/rtnetlink.h
index 3ebfcc6e56fd..7559020f760c 100644
--- a/include/net/rtnetlink.h
+++ b/include/net/rtnetlink.h
@@ -71,7 +71,7 @@ static inline int rtnl_msg_family(const struct nlmsghdr *nlh)
 /**
  *	struct rtnl_link_ops - rtnetlink link operations
  *
- *	@list: Used internally, protected by RTNL and SRCU
+ *	@list: Used internally, protected by link_ops_mutex and SRCU
  *	@srcu: Used internally
  *	@kind: Identifier
  *	@netns_refund: Physical device, move to init_net on netns exit