netdev - Re: [PATCH] virtio-net: fix a race on 32bit arches

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, 06 Jun 2012 19:13:02 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.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, 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.

There is no atomicity guarantee in SNMP counters. (Ie fetching tx_bytes
and tx_packets in a transaction is not mandatory in any RFC)

As long as there is no cumulative error, its OK.



--
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