linux-kernel - Re: [patch] revert: [NET]: Fix races in net_rx

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Message-ID: <20070719153217.GA25544@elte.hu>
Date:	Thu, 19 Jul 2007 17:32:18 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Olaf Kirch <olaf.kirch@...cle.com>
Cc:	Jarek Poplawski <jarkao2@...pl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, davem@...emloft.net,
	Auke Kok <auke-jan.h.kok@...el.com>
Subject: Re: [patch] revert: [NET]: Fix races in net_rx_action vs netpoll


* Ingo Molnar <mingo@...e.hu> wrote:

> ugh. Something really weird happened with this e1000 problem.
> 
> i crashed the laptop in a weird way and had to power-cycle it in an 
> unusual fashion. After that i wanted to try your latest BUG_ON() 
> theory but the network hang went away!
> 
> For 3 hours i tried to reproduce the hang (i went back to the original 
> git tree and the .config under which i found it, i power cycled it 
> again, i unplugged the power cord to make it go off battery, unplugged 
> the ethernet, recreated a completely new tree, etc. etc.) but with no 
> success! Total Heisenbug - and the really annoying thing is that you 
> just had a good theory about what might be happening. I'm now at 
> kernel build iteration #75 in this tree ...

ah! Just found the reason: the bug apparently depends on the precise 
kernel command-line contents. I accidentally dropped ignore_loglevel 
(found this while comparing with the older logs i sent to you), adding 
it back in produces hung networking too. So it appears that a netconsole 
printout while e1000 is initializing (or while some other networking 
component is initializing) might be the culprit?

	Ingo

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