From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: [PATCHv7 3/3] vhost_net: a kernel-level virtio server Date: Wed, 04 Nov 2009 12:08:47 +0100 Message-ID: <878wema6o0.fsf@basil.nowhere.org> References: <20091103172422.GD5591@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii 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 To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20091103172422.GD5591@redhat.com> (Michael S. Tsirkin's message of "Tue, 3 Nov 2009 19:24:23 +0200") Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org "Michael S. Tsirkin" writes: Haven't really read the whole thing, just noticed something at a glance. > +/* Expects to be always run from workqueue - which acts as > + * read-size critical section for our kind of RCU. */ > +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); I haven't gone over all this code in detail, but that isolated reference count use looks suspicious. What prevents the mm from going away before you increment, if it's not the current one? -Andi -- ak@linux.intel.com -- Speaking for myself only.