netdev - Re: [PATCH] netconsole: queue console messages to send later

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Date:	Mon, 7 Jun 2010 13:00:15 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Flavio Leitner <fleitner@...hat.com>, netdev@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Cong Wang <amwang@...hat.com>, Jay Vosburgh <fubar@...ibm.com>,
	Flavio Leitner <fbl@...close.org>,
	Andy Gospodarek <gospo@...hat.com>,
	Neil Horman <nhorman@...driver.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>,
	bridge@...ts.linux-foundation.org,
	bonding-devel@...ts.sourceforge.net
Subject: Re: [PATCH] netconsole: queue console messages to send later

On Mon, 07 Jun 2010 14:50:48 -0500
Matt Mackall <mpm@...enic.com> wrote:

> On Mon, 2010-06-07 at 16:24 -0300, Flavio Leitner wrote:
> > There are some networking drivers that hold a lock in the
> > transmit path. Therefore, if a console message is printed
> > after that, netconsole will push it through the transmit path,
> > resulting in a deadlock.
> 
> This is an ongoing pain we've known about since before introducing the
> netpoll code to the tree.
> 
> My take has always been that any form of queueing is contrary to the
> goal of netpoll: timely delivery of messages even during machine-killing
> situations like oopses. There may never be a second chance to deliver
> the message as the machine may be locked solid. And there may be no
> other way to get the message out of the box in such situations. Adding
> queueing is a throwing-the-baby-out-with-the-bathwater fix.
> 
> I think Dave agrees with me here, and I believe he's said in the past
> that drivers trying to print messages in such contexts should be
> considered buggy.
> 

Because it to hard to fix all possible device configurations.
There should be any way to detect recursion and just drop the message to
avoid deadlock.

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