lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Wed, 6 Jun 2012 21:43:52 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org,
	rusty@...tcorp.com.au, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Stephen Hemminger <shemminger@...tta.com>
Subject: Re: [PATCH] virtio-net: fix a race on 32bit arches

On Wed, Jun 06, 2012 at 07:13:02PM +0200, Eric Dumazet wrote:
> On Wed, 2012-06-06 at 19:17 +0300, Michael S. Tsirkin wrote:
> 
> > But why do you say at most 1 packet?
> > 
> > Consider get_stats doing:
> >                u64_stats_update_begin(&stats->syncp);
> >                stats->tx_bytes += skb->len;
> > 
> > on 64 bit at this point
> > tx_packets might get incremented any number of times, no?
> > 
> >                 stats->tx_packets++;
> >                 u64_stats_update_end(&stats->syncp);
> > 
> > now tx_bytes and tx_packets are out of sync by more than 1.
> 
> You lost me there.
> 
> No idea of what you are thinking about.

Sorry about that. This is not a bug. I am saying two things:

1. We are trying to look at counters for purposes of tuning the device.
E.g. if ethtool reports packets and bytes, we'd like to calculate
average packet size by bytes/packets.

If both counters are read atomically the metric becomes more exact.
Not a must but nice to have.

2. 32 bit systems have some overhead because of the seqlock.
virtio could instead simply keep tx counters in the queue structure, and
get the tx lock when they are read.


-- 
MST
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Powered by blists - more mailing lists