From: "David S. Miller" <davem@davemloft.net>
To: hadi@cyberus.ca
Cc: kaber@trash.net, tgraf@suug.ch, netdev@oss.sgi.com
Subject: Re: [PATCH] PKT_SCHED: dsmark must take care of shared/cloned skbs
Date: Mon, 20 Dec 2004 17:02:22 -0800 [thread overview]
Message-ID: <20041220170222.5ee14588.davem@davemloft.net> (raw)
In-Reply-To: <1103552026.1048.324.camel@jzny.localdomain>
On 20 Dec 2004 09:13:46 -0500
jamal <hadi@cyberus.ca> wrote:
> Certainly not a big deal; shouldnt care if once in a while tcpdump
> actually gets to see the real packet that went out the wire.
It's not just tcpdump. Any modification of a the packet data
for a shared SKB is illegal, no matter where it occurs.
This can corrupt TCP packets, which share the transmitted
packet with the socket retransmit queue.
We have a similar problem with TSO and some gigabit cards whose
drivers muck with the iphdr->tot_len field on transmit. I still
am not sure how I want to address that case yet. Since transmitted
TCP data packets are always shared/cloned, we'll have to do a data
copy on every TSO send on these cards which frankly nullifies much
of the performance gain TSO gives. If we end of fixing it via a copy
we'll probably need to seriously consider not doing TSO unless we
are doing sendfile.
next prev parent reply other threads:[~2004-12-21 1:02 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-12-18 17:00 [PATCH] PKT_SCHED: dsmark must take care of shared/cloned skbs Thomas Graf
2004-12-18 21:00 ` Thomas Graf
2004-12-19 20:23 ` jamal
2004-12-19 20:36 ` Thomas Graf
2004-12-19 22:53 ` jamal
2004-12-19 23:18 ` Thomas Graf
2004-12-20 8:06 ` Patrick McHardy
2004-12-20 14:13 ` jamal
2004-12-21 1:02 ` David S. Miller [this message]
2004-12-22 13:14 ` jamal
2004-12-22 13:50 ` Thomas Graf
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