linux-kernel - Re: [PATCH 1/7] introduce atomic_dec_and_lock

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Message-ID: <Pine.LNX.4.64.0608301352000.6761@scrub.home>
Date:	Wed, 30 Aug 2006 13:54:51 +0200 (CEST)
From:	Roman Zippel <zippel@...ux-m68k.org>
To:	Oleg Nesterov <oleg@...sign.ru>
cc:	Kirill Korotaev <dev@...ru>, Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Pavel Emelianov <xemul@...nvz.org>,
	Andrey Savochkin <saw@...ru>, devel@...nvz.org,
	Rik van Riel <riel@...hat.com>, Andi Kleen <ak@...e.de>,
	Alexey Dobriyan <adobriyan@...l.ru>,
	Matt Helsley <matthltc@...ibm.com>,
	CKRM-Tech <ckrm-tech@...ts.sourceforge.net>
Subject: Re: [PATCH 1/7] introduce atomic_dec_and_lock_irqsave()

Hi,

On Wed, 30 Aug 2006, Oleg Nesterov wrote:

> > AFAICT it's called via rcu, does that mean anything released via rcu has 
> > to be protected against interrupts?
> 
> RCU means softirq, probably we can use spin_lock_bh() to protect against deadlock.
> But free_uid() may be called with irqs disabled, we can't use local_bh_enable()
> in such a case.

Eek, I wasn't really aware of it and this would really suck. We should 
move things out of the interrupt context and not into it. :(
I would call it a bug in the rcu system.

bye, Roman
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