From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCHv7 3/3] vhost_net: a kernel-level virtio server Date: Tue, 03 Nov 2009 19:03:55 +0100 Message-ID: <4AF0708B.4020406@gmail.com> References: <20091103172422.GD5591@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: netdev@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@elte.hu, linux-mm@kvack.org, akpm@linux-foundation.org, hpa@zytor.com, gregory.haskins@gmail.com, Rusty Russell , s.hetze@linux-ag.com, "Paul E. McKenney" To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20091103172422.GD5591@redhat.com> Sender: owner-linux-mm@kvack.org List-Id: netdev.vger.kernel.org Michael S. Tsirkin a =E9crit : > +static void handle_tx(struct vhost_net *net) > +{ > + struct vhost_virtqueue *vq =3D &net->dev.vqs[VHOST_NET_VQ_TX]; > + unsigned head, out, in, s; > + struct msghdr msg =3D { > + .msg_name =3D NULL, > + .msg_namelen =3D 0, > + .msg_control =3D NULL, > + .msg_controllen =3D 0, > + .msg_iov =3D vq->iov, > + .msg_flags =3D MSG_DONTWAIT, > + }; > + size_t len, total_len =3D 0; > + int err, wmem; > + size_t hdr_size; > + struct socket *sock =3D rcu_dereference(vq->private_data); > + if (!sock) > + return; > + > + wmem =3D atomic_read(&sock->sk->sk_wmem_alloc); > + if (wmem >=3D 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) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org