netdev - Re: [PATCH] softirq: Use local_irq_save() in local_bh

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Message-ID: <20081117161617.GF12081@elte.hu>
Date:	Mon, 17 Nov 2008 17:16:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	Johannes Berg <johannes@...solutions.net>,
	David Miller <davem@...emloft.net>,
	Ferenc Wagner <wferi@...f.hu>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] softirq: Use local_irq_save() in local_bh_enable()


* Jarek Poplawski <jarkao2@...il.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 receive path is called by 
> netconsole, which simply turns off irqs around this all. Probably 
> this is wrong, but it worked like this long time, and it's not 
> trivial to fix this.
> 
> Anyway, a commit 0f476b6d91a1395bda6464e653ce66ea9bea7167 "softirq: 
> remove irqs_disabled warning from local_bh_enable" can break things 
> after changing from local_irq_save() to local_irq_disable(). Before 
> this commit there was only a warning, now a lockup is possible, so 
> it could be treated as a regression. This patch reverts the change 
> in irqs.

hm, but calling local_bh_enable() with hardirqs off is a bug. It might 
be a long-standing bug, but it can cause lockups even with that change 
reverted: when we process softirqs in local_bh_enable(). So why not 
fix the bug instead?

	Ingo
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