From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id 8318C6B0044 for ; Tue, 3 Nov 2009 14:58:59 -0500 (EST) Date: Tue, 3 Nov 2009 21:55:57 +0200 From: "Michael S. Tsirkin" Subject: Re: [PATCHv7 3/3] vhost_net: a kernel-level virtio server Message-ID: <20091103195557.GA6669@redhat.com> References: <20091103172422.GD5591@redhat.com> <4AF0708B.4020406@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4AF0708B.4020406@gmail.com> Sender: owner-linux-mm@kvack.org To: Eric Dumazet 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" List-ID: On Tue, Nov 03, 2009 at 07:03:55PM +0100, Eric Dumazet wrote: > Michael S. Tsirkin a ecrit : > > +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@linux.vnet.ibm.com) as well. There are many ways to use RCU not all of which involve read_rcu_lock. -- 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