Re: 2.6.13-rc4 - kernel panic - BUG at net/ipv4/tcp_output.c:918

[Herbert Xu]

On Mon, Aug 01, 2005 at 08:33:20AM +0000, Guillaume Pelat wrote:
> 
> I just tried the patch attached. :)
> 
> The bug is still here (same symptoms), with a slightly different backtrace :
> ------------[ cut here ]------------
> kernel BUG at net/ipv4/tcp_output.c:918!

OK, let's try again :)

I bet it's the tcp_enter_cwr() call in tcp_transmit_skb().  So
the sequence is:

tcp_write_xmit
	cwnd_quota = tcp_cwnd_test
	tcp_transmit_skb
		tcp_enter_cwr
			tp->snd_cwnd = min(tp->snd_cwnd, in_flight + 1)

At this point cwnd_quota is out-of-sync with tp->snd_cwnd.

	cwnd_quota -= tcp_skb_pcount(skb)
	cwnd_quota > 0
	tcp_tso_should_defer
		BUG since tp->snd_cwnd is smaller than what
		cwnd_quota indicated.

So I suppose we should reset cwnd_quota after tcp_transmit_skb?

Perhaps we should only transmit one MSS in this case?

Cheers,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@xxxxxxxxxxxxxxxxxxx>
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