From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH] l2tp: cast l2tp traffic counter to unsigned Date: Sat, 10 Jun 2017 16:13:35 -0400 (EDT) Message-ID: <20170610.161335.734544822657172006.davem@davemloft.net> References: <20170609142947.16969-1-dheidler@suse.de> <20170609151621.11e610a2@xeon-e3> <1497054551.736.99.camel@edumazet-glaptop3.roam.corp.google.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: stephen@networkplumber.org, dheidler@suse.de, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, tparkin@katalix.com To: eric.dumazet@gmail.com Return-path: In-Reply-To: <1497054551.736.99.camel@edumazet-glaptop3.roam.corp.google.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org From: Eric Dumazet Date: Fri, 09 Jun 2017 17:29:11 -0700 > On Fri, 2017-06-09 at 15:16 -0700, Stephen Hemminger wrote: >> On Fri, 9 Jun 2017 16:29:47 +0200 >> Dominik Heidler wrote: >> >> > This fixes a counter problem on 32bit systems: >> > When the rx_bytes counter reached 2 GiB, it jumpd to (2^64 Bytes - 2GiB) Bytes. >> > >> > rtnl_link_stats64 has __u64 type and atomic_long_read returns >> > atomic_long_t which is signed. Due to the conversation >> > we get an incorrect value on 32bit systems if the MSB of >> > the atomic_long_t value is set. >> > >> > CC: Tom Parkin >> > Fixes: 7b7c0719cd7a ("l2tp: avoid deadlock in l2tp stats update") >> > Signed-off-by: Dominik Heidler >> > --- >> > net/l2tp/l2tp_eth.c | 13 +++++++------ >> > 1 file changed, 7 insertions(+), 6 deletions(-) >> > >> > diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c >> > index 8b21af7321b9..668a75e002e9 100644 >> > --- a/net/l2tp/l2tp_eth.c >> > +++ b/net/l2tp/l2tp_eth.c >> > @@ -114,12 +114,13 @@ static void l2tp_eth_get_stats64(struct net_device *dev, >> > { >> > struct l2tp_eth *priv = netdev_priv(dev); >> > >> > - stats->tx_bytes = atomic_long_read(&priv->tx_bytes); >> > - stats->tx_packets = atomic_long_read(&priv->tx_packets); >> > - stats->tx_dropped = atomic_long_read(&priv->tx_dropped); >> > - stats->rx_bytes = atomic_long_read(&priv->rx_bytes); >> > - stats->rx_packets = atomic_long_read(&priv->rx_packets); >> > - stats->rx_errors = atomic_long_read(&priv->rx_errors); >> > + stats->tx_bytes = (unsigned long) atomic_long_read(&priv->tx_bytes); >> > + stats->tx_packets = (unsigned long) atomic_long_read(&priv->tx_packets); >> > + stats->tx_dropped = (unsigned long) atomic_long_read(&priv->tx_dropped); >> > + stats->rx_bytes = (unsigned long) atomic_long_read(&priv->rx_bytes); >> > + stats->rx_packets = (unsigned long) atomic_long_read(&priv->rx_packets); >> > + stats->rx_errors = (unsigned long) atomic_long_read(&priv->rx_errors); >> > + >> > } >> > >> > static const struct net_device_ops l2tp_eth_netdev_ops = { >> >> This is not the right way to fix this. >> >> 1. shouldn't be using atomic's for network counters, look at other network devices. >> >> 2. should be using u64_stats_fetch api to handle 64 bit counters. > > But they do not want 64bit counters, and not per cpu counters for a > driver handling few packets per second. > > Just use native size of "unsigned long". Ahh yeah, indeed. I've applied this l2tp patch, therefore. > We use the same atomic_long_t for (struct netdev)->rx_dropped, > tx_dropped & rx_nohandler > > So I guess same fix is needed in dev_get_stats() Looks like it, I'll apply a formal submission of this.