From: David Miller <davem@davemloft.net>
To: eric.dumazet@gmail.com
Cc: subramanian.vijay@gmail.com, therbert@google.com, netdev@vger.kernel.org
Subject: Re: Bug in computing data_len in tcp_sendmsg?
Date: Fri, 02 Dec 2011 13:40:40 -0500 (EST) [thread overview]
Message-ID: <20111202.134040.638198723589712419.davem@davemloft.net> (raw)
In-Reply-To: <1322850989.2762.47.camel@edumazet-laptop>
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Fri, 02 Dec 2011 19:36:29 +0100
> What I ask now is following problem (even prior to my frag allocation
> patch) :
>
> 1) We allocate a linear skb (SG being off) to cook a tcp frame of length
> XXX bytes.
>
> 2) We send it.
>
> 3) We receive an ACK for first 31 bytes.
>
> 4) We trim 31 bytes from the head of skb. (skb_pull(skb, 31))
> skb->data is now not anymore aligned to a 4 bytes boundary.
>
> 5) Later, we need to retransmit skb (XXX minus 31 bytes already ACKed)
> We push TCP header, and skb->data is not aligned.
> TCP header is not aligned anymore. x86 doesnt care, but what about
> other arches with misalign traps ?
Yes, for non-SG this always was technically possible.
But now you've made it possible for SG too.
Frankly, I think we should:
1) Revert your patch, so it's not possible for SG once more.
2) Add code to reallocate the SKB linear data when this happens in
the non-SG case.
next prev parent reply other threads:[~2011-12-02 18:40 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-01 1:48 Bug in computing data_len in tcp_sendmsg? Tom Herbert
2011-12-01 3:42 ` Eric Dumazet
2011-12-01 4:06 ` Tom Herbert
2011-12-01 4:16 ` David Miller
2011-12-01 4:17 ` Eric Dumazet
2011-12-01 5:09 ` Tom Herbert
2011-12-01 9:15 ` Eric Dumazet
2011-12-01 17:29 ` Jesse Brandeburg
2011-12-01 18:04 ` David Miller
2011-12-01 20:37 ` Eric Dumazet
2011-12-01 22:18 ` Vijay Subramanian
2011-12-01 22:30 ` Eric Dumazet
2011-12-02 6:18 ` Vijay Subramanian
2011-12-02 11:59 ` Eric Dumazet
2011-12-02 15:44 ` Eric Dumazet
2011-12-02 16:05 ` Eric Dumazet
2011-12-02 18:13 ` David Miller
2011-12-02 18:36 ` Eric Dumazet
2011-12-02 18:40 ` David Miller [this message]
2011-12-02 20:22 ` Eric Dumazet
2011-12-02 20:24 ` David Miller
2011-12-02 20:45 ` Eric Dumazet
2011-12-02 20:48 ` Eric Dumazet
2011-12-02 21:30 ` David Miller
2011-12-03 15:09 ` Eric Dumazet
2011-12-04 7:39 ` [PATCH] tcp: take care of misalignments Eric Dumazet
2011-12-04 18:21 ` David Miller
2011-12-04 18:51 ` Eric Dumazet
2011-12-05 23:45 ` David Miller
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