netdev - Re: [Bugme-new] [Bug 38102] New: BUG kmalloc-2048: Poison overwritten

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Date:	Tue, 05 Jul 2011 06:38:28 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexey Zaytsev <alexey.zaytsev@...il.com>
Cc:	Michael Büsch <m@...s.ch>,
	Andrew Morton <akpm@...ux-foundation.org>,
	netdev@...r.kernel.org, Gary Zambrano <zambrano@...adcom.com>,
	bugme-daemon@...zilla.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Pekka Pietikainen <pp@...oulu.fi>,
	Florian Schirmer <jolt@...box.org>,
	Felix Fietkau <nbd@...nwrt.org>, Michael Buesch <mb@...sch.de>
Subject: Re: [Bugme-new] [Bug 38102] New: BUG kmalloc-2048: Poison
 overwritten

Le mardi 05 juillet 2011 à 08:29 +0400, Alexey Zaytsev a écrit :
> On Tue, Jul 5, 2011 at 08:25, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > Le mardi 05 juillet 2011 à 08:17 +0400, Alexey Zaytsev a écrit :
> >> >
> >> Check out starting at packet 302893. 383 _identical_ ACKs were sent
> >> out by the b44 machine within 30 milliseconds.
> >
> >
> > As I said, b44 driver lost at least 200 consecutive frames (source says
> > recovery takes about 20 ms)
> >
> > TCP then do its normal job.
> >
> 
> From my understanding, after a frame is lost, TCP would be waiting for
> a retransmit. Or at least, it would not be sending 400 duplicate ACKs
> for the single last frame received, right? Let me run tcpdump on the
> b44 side now. I'm quite sure I won't see any ACK dups leaving the
> stack.

Wow, I believe you are on a wrong track. Honestly.

Try to unpplug the wire for 100ms, and watch your "duplicate acks
disease".

Thats exactly what is happening with b44 driver doing a "fast recovery"
right now.

Thats a moot point. Running tcpdump on your b44 machine will kill your
performance even more, it wont solve the b44 bug.

If you prefer to 'fix tcp', please open another thread.



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