Re: [Qemu-devel] [PATCH] rcu: actually register threads that have RCU read-side critical sections

[Paolo Bonzini <pbonzini@redhat.com>]

On 24/07/2015 07:56, Wen Congyang wrote:
> @@ -115,9 +116,12 @@ static void wait_for_readers(void)
>          }
>  
>          /* Wait for one thread to report a quiescent state and
> -         * try again.
> +         * try again. Release rcu_gp_lock, so rcu_(un)register_thread()
> +         * doesn't wait too much time.
>           */
> +        qemu_mutex_unlock(&rcu_gp_lock);
>          qemu_event_wait(&rcu_gp_event);
> +        qemu_mutex_lock(&rcu_gp_lock);
>      }
>  

So in this case rcu_unregister_thread could actually remove the node
from synchronize_rcu's qsreaders, not just from registry.  That's a bit
tricky, but it should work.  Please add a comment, however.

Also, please rename "rcu_gp_lock" as well to rcu_registry_lock.  We'll
get the patches in QEMU 2.5.

Paolo