From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with SMTP id 0A1886B004D for ; Tue, 3 Nov 2009 13:08:33 -0500 (EST) Received: by ywh26 with SMTP id 26so6004857ywh.12 for ; Tue, 03 Nov 2009 10:08:32 -0800 (PST) Message-ID: <4AF07199.2020601@gmail.com> Date: Tue, 03 Nov 2009 13:08:25 -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> In-Reply-To: <4AF0708B.4020406@gmail.com> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig77CFE234DE15F23B398FB30F" 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) --------------enig77CFE234DE15F23B398FB30F Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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); >> + >=20 > using rcu_dereference() and mutex_lock() at the same time seems wrong, = I suspect > that your use of RCU is not correct. >=20 > 1) rcu_dereference() should be done inside a read_rcu_lock() section, a= nd > 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,= ) >=20 > 2) mutex_lock() can sleep (ie block) >=20 Michael, I warned you that this needed better documentation ;) 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. Kind Regards, -Greg --------------enig77CFE234DE15F23B398FB30F 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/ iEYEARECAAYFAkrwcZkACgkQP5K2CMvXmqGhOACePT9ytdQxnqeObfA1h+nnRfJY vNwAn2y4p+io84eG19OyEly9IqSi8EDf =XPsn -----END PGP SIGNATURE----- --------------enig77CFE234DE15F23B398FB30F-- -- 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