Hello Gur!

On Tue, 2024-09-17 at 11:10 +0300, Gur Stavi wrote:

quoted

@@ -1594,10 +1592,11 @@ void dsa_switch_shutdown(struct dsa_switch *ds)

  	}

  	/* Disconnect from further netdevice notifiers on the conduit,
-	 * since netdev_uses_dsa() will now return false.
+	 * from now on, netdev_uses_dsa_currently() will return false.
  	 */
  	dsa_switch_for_each_cpu_port(dp, ds)
-		dp->conduit->dsa_ptr = NULL;
+		rcu_assign_pointer(dp->conduit->dsa_ptr, NULL);
+	synchronize_rcu();

  	rtnl_unlock();
  out:

Hi, I am a newbie here. Thanks for the opportunity for learning more
about rcu.
Wouldn't it make more sense to call synchronize_rcu after rtnl_unlock?

This is indeed a question which is usually resolved other way around
(making locked section shorter), but in this particular case I thought that:
- we actually don't need giving rtnl lock sooner, which would potentially
  make synchronize_rcu() call longer (if another thread manages to wake up
  and claim the rtnl lock before synchronize_rcu())
- we are in shutdown phase, we don't need to minimize lock contention, we
  need to minimize the overall shutdown time

-- 
Alexander Sverdlin
Siemens AG
www.siemens.com