From: Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH] netconsole: Disable softirqs in write_msg()
Date: Wed, 19 Nov 2008 10:30:04 +0100
Message-ID: <20081119093004.GD22309@elte.hu>
References: <87y6zwwy5c.fsf@tac.ki.iif.hu> <20081119084106.GA6699@ff.dom.local>
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Cc: David Miller <davem@davemloft.net>, Jeff Garzik <jeff@garzik.org>,
	Johannes Berg <johannes@sipsolutions.net>,
	Ferenc Wagner <wferi@niif.hu>, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org
To: Jarek Poplawski <jarkao2@gmail.com>
Content-Disposition: inline
In-Reply-To: <20081119084106.GA6699@ff.dom.local>
Sender: netdev-owner@vger.kernel.org


* Jarek Poplawski <jarkao2@gmail.com> wrote:

> This report: http://marc.info/?l=linux-netdev&m=122599341430090&w=2
> shows local_bh_enable() is used in the wrong context (irqs disabled).
> It happens when a usual network path is called by netconsole, which
> simply turns off hardirqs around this all.
> 
> This patch additionally disables softirqs to avoid possibility of
> enabling bh and calling do_softirq() with hardirqs disabled.
> 
> Reported-by: Ferenc Wagner <wferi@niif.hu>
> Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
> ---
> 
>  drivers/net/netconsole.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
> index d304d38..f6ecad8 100644
> --- a/drivers/net/netconsole.c
> +++ b/drivers/net/netconsole.c
> @@ -702,6 +702,8 @@ static void write_msg(struct console *con, const char *msg, unsigned int len)
>  	if (list_empty(&target_list))
>  		return;
>  
> +	/* Avoid enabling softirqs with hardirqs disabled */
> +	local_bh_disable();
>  	spin_lock_irqsave(&target_list_lock, flags);
>  	list_for_each_entry(nt, &target_list, list) {
>  		netconsole_target_get(nt);
> @@ -723,6 +725,7 @@ static void write_msg(struct console *con, const char *msg, unsigned int len)
>  		netconsole_target_put(nt);
>  	}
>  	spin_unlock_irqrestore(&target_list_lock, flags);
> +	local_bh_enable();

but netconsole can be triggered from printk - and printk can be called 
from hardirqs-off sections - so this doesnt really fix the bug. 
Netconsole should not do BH processing.

	Ingo