From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH] l2tp: cast l2tp traffic counter to unsigned Date: Fri, 09 Jun 2017 17:29:11 -0700 Message-ID: <1497054551.736.99.camel@edumazet-glaptop3.roam.corp.google.com> References: <20170609142947.16969-1-dheidler@suse.de> <20170609151621.11e610a2@xeon-e3> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Dominik Heidler , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Tom Parkin To: Stephen Hemminger Return-path: Received: from mail-pf0-f193.google.com ([209.85.192.193]:34399 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751712AbdFJA3O (ORCPT ); Fri, 9 Jun 2017 20:29:14 -0400 In-Reply-To: <20170609151621.11e610a2@xeon-e3> Sender: netdev-owner@vger.kernel.org List-ID: 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". 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() diff --git a/net/core/dev.c b/net/core/dev.c index 54bb8d99d26afcc1a9c5a56f1e8c2d1f6e06db98..1a66a8761f9a579c9bf6b6ab5b1415770adcf76b 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -7785,9 +7785,9 @@ struct rtnl_link_stats64 *dev_get_stats(struct net_device *dev, } else { netdev_stats_to_stats64(storage, &dev->stats); } - storage->rx_dropped += atomic_long_read(&dev->rx_dropped); - storage->tx_dropped += atomic_long_read(&dev->tx_dropped); - storage->rx_nohandler += atomic_long_read(&dev->rx_nohandler); + storage->rx_dropped += (unsigned long)atomic_long_read(&dev->rx_dropped); + storage->tx_dropped += (unsigned long)atomic_long_read(&dev->tx_dropped); + storage->rx_nohandler += (unsigned long)atomic_long_read(&dev->rx_nohandler); return storage; } EXPORT_SYMBOL(dev_get_stats);