From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id 53EB46B0044 for ; Tue, 3 Nov 2009 13:14:14 -0500 (EST) Received: by gxk24 with SMTP id 24so2386828gxk.6 for ; Tue, 03 Nov 2009 10:14:12 -0800 (PST) Message-ID: <4AF072EE.9020202@gmail.com> Date: Tue, 03 Nov 2009 13:14:06 -0500 From: Gregory Haskins MIME-Version: 1.0 Subject: Re: [PATCHv7 3/3] vhost_net: a kernel-level virtio server References: <20091103172422.GD5591@redhat.com> <4AF0708B.4020406@gmail.com> <4AF07199.2020601@gmail.com> In-Reply-To: <4AF07199.2020601@gmail.com> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigE18A8C89AC1232EB011669F5" Sender: owner-linux-mm@kvack.org To: Eric Dumazet Cc: "Michael S. Tsirkin" , 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, Rusty Russell , s.hetze@linux-ag.com, "Paul E. McKenney" List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigE18A8C89AC1232EB011669F5 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Gregory Haskins wrote: > Eric Dumazet wrote: >> 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) >> >=20 >=20 > Michael, > I warned you that this needed better documentation ;) >=20 > Eric, > I think I flagged this once before, but Michael convinced me that it > was indeed "ok", if but perhaps a bit unconventional. I will try to > find the thread. >=20 > Kind Regards, > -Greg >=20 Here it is: http://lkml.org/lkml/2009/8/12/173 Kind Regards, -Greg --------------enigE18A8C89AC1232EB011669F5 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.11 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkrwcu4ACgkQP5K2CMvXmqH6LQCfYPH0ZOpy6lFQqLyJiRpczJJt 1L4Anjn/hFabGiOof5cYTbyAv9fZr2fM =UyNc -----END PGP SIGNATURE----- --------------enigE18A8C89AC1232EB011669F5-- -- 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