On Tue, Nov 03, 2009 at 07:03:55PM +0100, Eric Dumazet wrote: > Michael S. Tsirkin a écrit : > > +static void handle_tx(struct vhost_net *net) > > +{ > > + struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX]; > > + unsigned head, out, in, s; > > + struct msghdr msg = { > > + .msg_name = NULL, > > + .msg_namelen = 0, > > + .msg_control = NULL, > > + .msg_controllen = 0, > > + .msg_iov = vq->iov, > > + .msg_flags = MSG_DONTWAIT, > > + }; > > + size_t len, total_len = 0; > > + int err, wmem; > > + size_t hdr_size; > > + struct socket *sock = rcu_dereference(vq->private_data); > > + if (!sock) > > + return; > > + > > + wmem = atomic_read(&sock->sk->sk_wmem_alloc); > > + if (wmem >= sock->sk->sk_sndbuf) > > + return; > > + > > + use_mm(net->dev.mm); > > + mutex_lock(&vq->mutex); > > + vhost_no_notify(vq); > > + > > using rcu_dereference() and mutex_lock() at the same time seems wrong, I suspect > that your use of RCU is not correct. > > 1) rcu_dereference() should be done inside a read_rcu_lock() section, and > we are not allowed to sleep in such a section. > (Quoting Documentation/RCU/whatisRCU.txt : > It is illegal to block while in an RCU read-side critical section, ) > > 2) mutex_lock() can sleep (ie block) This use is correct. See comment in vhost.h This use of RCU has been acked by Paul E. McKenney (paulmck@xxxxxxxxxxxxxxxxxx) as well. There are many ways to use RCU not all of which involve read_rcu_lock. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html